22. USB on-the-go full-speed (OTG_FS)

22.1 OTG_FS introduction

Portions Copyright (c) 2004, 2005 Synopsys, Inc. All rights reserved. Used with permission.

This section presents the architecture and the programming model of the OTG_FS controller.

The following acronyms are used throughout this section:

References are made to the following documents:

• • USB On-The-Go Supplement, Revision 1.3
• • Universal Serial Bus Revision 2.0 Specification

The OTG_FS is a dual-role device (DRD) controller that supports both device and host functions and is fully compliant with the On-The-Go Supplement to the USB 2.0 Specification . It can also be configured as a host-only or device-only controller, fully compliant with the USB 2.0 Specification . In host mode, the OTG_FS supports full-speed (FS, 12 Mbits/s) and low-speed (LS, 1.5 Mbits/s) transfers whereas in device mode, it only supports full-speed (FS, 12 Mbits/s) transfers. The OTG_FS supports both HNP and SRP. The only external device required is a charge pump for \( V_{BUS} \) in host mode.

22.2 OTG_FS main features

The main features can be divided into three categories: general, host-mode and device-mode features.

22.2.1 General features

The OTG_FS interface general features are the following:

• • It is USB-IF certified to the Universal Serial Bus Specification Rev 2.0
• • It includes full support (PHY) for the optional On-The-Go (OTG) protocol detailed in the On-The-Go Supplement Rev 1.3 specification
  • – Integrated support for A-B Device Identification (ID line)
  • – Integrated support for host Negotiation Protocol (HNP) and Session Request Protocol (SRP)
  • – It allows host to turn \( V_{BUS} \) off to conserve battery power in OTG applications
  • – It supports OTG monitoring of \( V_{BUS} \) levels with internal comparators
  • – It supports dynamic host-peripheral switch of role
• • It is software-configurable to operate as:
  • – SRP capable USB FS Peripheral (B-device)
  • – SRP capable USB FS/LS host (A-device)
  • – USB On-The-Go Full-Speed Dual Role device
• • It supports FS SOF and LS Keep-alives with
  • – SOF pulse PAD connectivity (OTG_FS_SOF)
  • – SOF pulse internal connection to timer2 (TIM2)
  • – Configurable framing period
  • – Configurable end of frame interrupt
• • It includes power saving features such as system stop during USB Suspend, switch-off of clock domains internal to the digital core, PHY and DFIFO power management
• • It features a dedicated RAM of 1.25 Kbytes with advanced FIFO control:
  • – Configurable partitioning of RAM space into different FIFOs for flexible and efficient use of RAM
  • – Each FIFO can hold multiple packets
  • – Dynamic memory allocation
  • – Configurable FIFO sizes that are not powers of 2 to allow the use of contiguous memory locations
• • It guarantees max USB bandwidth for up to one frame (1ms) without system intervention

22.2.2 Host-mode features

The OTG_FS interface main features and requirements in host-mode are the following:

• • External charge pump for V _BUS voltage generation.
• • Up to 8 host channels (pipes): each channel is dynamically reconfigurable to allocate any type of USB transfer.
• • Built-in hardware scheduler holding:
  • – Up to 8 interrupt plus isochronous transfer requests in the periodic hardware queue
  • – Up to 8 control plus bulk transfer requests in the non-periodic hardware queue
• • Management of a shared RX FIFO, a periodic TX FIFO and a nonperiodic TX FIFO for efficient usage of the USB data RAM.

22.2.3 Peripheral-mode features

The OTG_FS interface main features in peripheral-mode are the following:

• • 1 bidirectional control endpoint0
• • 3 IN endpoints (EPs) configurable to support Bulk, Interrupt or Isochronous transfers
• • 3 OUT endpoints configurable to support Bulk, Interrupt or Isochronous transfers
• • Management of a shared Rx FIFO and a Tx-OUT FIFO for efficient usage of the USB data RAM
• • Management of up to 4 dedicated Tx-IN FIFOs (one for each active IN EP) to put less load on the application
• • Support for the soft disconnect feature.

22.3 OTG_FS functional description

Figure 242. OTG full-speed block diagram

MS19928V4

22.3.1 OTG pins

Table 126. OTG_FS input/output pins

22.3.2 OTG full-speed core

The USB OTG FS receives the 48 MHz \( \pm 0.25\% \) clock from the reset and clock controller (RCC), via an external quartz. The USB clock is used for driving the 48 MHz domain at full-speed (12 Mbit/s) and must be enabled prior to configuring the OTG FS core.

The CPU reads and writes from/to the OTG FS core registers through the AHB peripheral bus. It is informed of USB events through the single USB OTG interrupt line described in Section 22.15: OTG_FS interrupts .

The CPU submits data over the USB by writing 32-bit words to dedicated OTG_FS locations (push registers). The data are then automatically stored into Tx-data FIFOs configured within the USB data RAM. There is one Tx-FIFO push register for each in-endpoint (peripheral mode) or out-channel (host mode).

The CPU receives the data from the USB by reading 32-bit words from dedicated OTG_FS addresses (pop registers). The data are then automatically retrieved from a shared Rx-FIFO configured within the 1.25 KB USB data RAM. There is one Rx-FIFO pop register for each out-endpoint or in-channel.

The USB protocol layer is driven by the serial interface engine (SIE) and serialized over the USB by the full-/low-speed transceiver module within the on-chip physical layer (PHY).

22.3.3 Full-speed OTG PHY

The embedded full-speed OTG PHY is controlled by the OTG FS core and conveys USB control & data signals through the full-speed subset of the UTMI+ Bus (UTMIFS). It provides the physical support to USB connectivity.

The full-speed OTG PHY includes the following components:

• • FS/LS transceiver module used by both host and device. It directly drives transmission and reception on the single-ended USB lines.
• • integrated ID pull-up resistor used to sample the ID line for A/B device identification.
• • DP/DM integrated pull-up and pull-down resistors controlled by the OTG_FS core depending on the current role of the device. As a peripheral, it enables the DP pull-up resistor to signal full-speed peripheral connections as soon as \( V_{BUS} \) is sensed to be at a valid level (B-session valid). In host mode, pull-down resistors are enabled on both DP/DM. Pull-up and pull-down resistors are dynamically switched when the device’s role is changed via the host negotiation protocol (HNP).
• • Pull-up/pull-down resistor ECN circuit. The DP pull-up consists of 2 resistors controlled separately from the OTG_FS as per the resistor Engineering Change Notice applied to USB Rev2.0. The dynamic trimming of the DP pull-up strength allows for better noise rejection and Tx/Rx signal quality.
• • \( V_{BUS} \) sensing comparators with hysteresis used to detect \( V_{BUS} \) Valid, A-B Session Valid and session-end voltage thresholds. They are used to drive the session request protocol (SRP), detect valid startup and end-of-session conditions, and constantly monitor the \( V_{BUS} \) supply during USB operations.
• • \( V_{BUS} \) pulsing method circuit used to charge/discharge \( V_{BUS} \) through resistors during the SRP (weak drive).

Caution: To guarantee a correct operation for the USB OTG FS peripheral, the AHB frequency should be higher than 14.2 MHz.

22.4 OTG dual role device (DRD)

Figure 243. OTG A-B device connection

1. 1. External voltage regulator only needed when building a \( V_{BUS} \) powered device
2. 2. STMP2141STR needed only if the application has to support a \( V_{BUS} \) powered device. A basic power switch can be used if 5 V are available on the application board.

22.4.1 ID line detection

The host or peripheral (the default) role is assumed depending on the ID input pin (OTG_FS_ID). The ID line status is determined on plugging in the USB, depending on which side of the USB cable is connected to the micro-AB receptacle.

• • If the B-side of the USB cable is connected with a floating ID wire, the integrated pull-up resistor detects a high ID level and the default Peripheral role is confirmed. In this configuration the OTG_FS complies with the standard FSM described by section 6.8.2: On-The-Go B-device of the On-The-Go Specification Rev1.3 supplement to the USB2.0.
• • If the A-side of the USB cable is connected with a grounded ID, the OTG_FS issues an ID line status change interrupt (CIDSCHG bit in OTG_FS_GINTSTS) for host software initialization, and automatically switches to the host role. In this configuration the OTG_FS complies with the standard FSM described by section 6.8.1: On-The-Go A-device of the On-The-Go Specification Rev1.3 supplement to the USB2.0.

22.4.2 HNP dual role device

The HNP capable bit in the Global USB configuration register (HNPCAP bit in OTG_FS_GUSBCFG) enables the OTG_FS core to dynamically change its role from A-host to A-peripheral and vice-versa, or from B-Peripheral to B-host and vice-versa according to the host negotiation protocol (HNP). The current device status can be read by the combined values of the Connector ID Status bit in the Global OTG control and status register (CIDSTS bit in OTG_FS_GOTGCTL) and the current mode of operation bit in the global interrupt and status register (CMOD bit in OTG_FS_GINTSTS).

The HNP program model is described in detail in Section 22.17: OTG_FS programming model .

22.4.3 SRP dual role device

The SRP capable bit in the global USB configuration register (SRPCAP bit in OTG_FS_GUSBCFG) enables the OTG_FS core to switch off the generation of \( V_{BUS} \) for the A-device to save power. Note that the A-device is always in charge of driving \( V_{BUS} \) regardless of the host or peripheral role of the OTG_FS.

the SRP A/B-device program model is described in detail in Section 22.17: OTG_FS programming model .

22.5 USB peripheral

This section gives the functional description of the OTG_FS in the USB peripheral mode. The OTG_FS works as an USB peripheral in the following circumstances:

• • OTG B-Peripheral
  • – OTG B-device default state if B-side of USB cable is plugged in
• • OTG A-Peripheral
  • – OTG A-device state after the HNP switches the OTG_FS to its peripheral role
• • B-device
  • – If the ID line is present, functional and connected to the B-side of the USB cable, and the HNP-capable bit in the Global USB Configuration register (HNPCAP bit in OTG_FS_GUSBCFG) is cleared (see On-The-Go Rev1.3 par. 6.8.3).
• • Peripheral only (see Figure 244: USB peripheral-only connection )
  • – The force device mode bit in the Global USB configuration register (FDMOD in OTG_FS_GUSBCFG) is set to 1, forcing the OTG_FS core to work as a USB peripheral-only (see On-The-Go Rev1.3 par. 6.8.3). In this case, the ID line is ignored even if present on the USB connector.

Note: To build a bus-powered device implementation in case of the B-device or peripheral-only configuration, an external regulator has to be added that generates the \( V_{DD} \) chip-supply from \( V_{BUS} \) .

The \( V_{BUS} \) pin can be freed by disabling the \( V_{BUS} \) sensing option. This is done by setting the NOVBUSSENS bit in the OTG_FS_GCCFG register. In this case the \( V_{BUS} \) is considered internally to be always at \( V_{BUS} \) valid level (5 V).

Figure 244. USB peripheral-only connection

1. 1. Use a regulator to build a bus-powered device.

22.5.1 SRP-capable peripheral

The SRP capable bit in the Global USB configuration register (SRPCAP bit in OTG_FS_GUSBCFG) enables the OTG_FS to support the session request protocol (SRP). In this way, it allows the remote A-device to save power by switching off \( V_{BUS} \) while the USB session is suspended.

The SRP peripheral mode program model is described in detail in the B-device session request protocol section.

22.5.2 Peripheral states

Powered state

The \( V_{BUS} \) input detects the B-Session valid voltage by which the USB peripheral is allowed to enter the powered state (see USB2.0 par9.1). The OTG_FS then automatically connects the DP pull-up resistor to signal full-speed device connection to the host and generates the session request interrupt (SRQINT bit in OTG_FS_GINTSTS) to notify the powered state.

The \( V_{BUS} \) input also ensures that valid \( V_{BUS} \) levels are supplied by the host during USB operations. If a drop in \( V_{BUS} \) below B-session valid happens to be detected (for instance because of a power disturbance or if the host port has been switched off), the OTG_FS automatically disconnects and the session end detected (SEDET bit in OTG_FS_GOTGINT) interrupt is generated to notify that the OTG_FS has exited the powered state.

In the powered state, the OTG_FS expects to receive some reset signaling from the host. No other USB operation is possible. When a reset signaling is received the reset detected interrupt (USBRST in OTG_FS_GINTSTS) is generated. When the reset signaling is complete, the enumeration done interrupt (ENUMDNE bit in OTG_FS_GINTSTS) is generated and the OTG_FS enters the Default state.

Soft disconnect

The powered state can be exited by software with the soft disconnect feature. The DP pull-up resistor is removed by setting the soft disconnect bit in the device control register (SDIS bit in OTG_FS_DCTL), causing a device disconnect detection interrupt on the host side even though the USB cable was not really removed from the host port.

Default state

In the Default state the OTG_FS expects to receive a SET_ADDRESS command from the host. No other USB operation is possible. When a valid SET_ADDRESS command is decoded on the USB, the application writes the corresponding number into the device address field in the device configuration register (DAD bit in OTG_FS_DCFG). The OTG_FS then enters the address state and is ready to answer host transactions at the configured USB address.

Suspended state

The OTG_FS peripheral constantly monitors the USB activity. After counting 3 ms of USB idleness, the early suspend interrupt (ESUSP bit in OTG_FS_GINTSTS) is issued, and confirmed 3 ms later, if appropriate, by the suspend interrupt (USBSUSP bit in OTG_FS_GINTSTS). The device suspend bit is then automatically set in the device status register (SUSPSTS bit in OTG_FS_DSTS) and the OTG_FS enters the suspended state.

The suspended state may optionally be exited by the device itself. In this case the application sets the remote wake-up signaling bit in the device control register (RWUSIG bit in OTG_FS_DCTL) and clears it after 1 to 15 ms.

When a resume signaling is detected from the host, the resume interrupt (WKUPINT bit in OTG_FS_GINTSTS) is generated and the device suspend bit is automatically cleared.

22.5.3 Peripheral endpoints

The OTG_FS core instantiates the following USB endpoints:

• • Control endpoint 0:
  • – Bidirectional and handles control messages only
  • – Separate set of registers to handle in and out transactions
  • – Proper control (OTG_FS_DIEPCTL0/OTG_FS_DOEPCTL0), transfer configuration (OTG_FS_DIEPTSIZ0/OTG_FS_DOEPTSIZ0), and status-interrupt (OTG_FS_DIEPINTx/OTG_FS_DOEPINT0) registers. The available set of bits inside the control and transfer size registers slightly differs from that of other endpoints
• • 3 IN endpoints
  • – Each of them can be configured to support the isochronous, bulk or interrupt transfer type
  • – Each of them has proper control (OTG_FS_DIEPCTLx), transfer configuration (OTG_FS_DIEPTSIZx), and status-interrupt (OTG_FS_DIEPINTx) registers
  • – The Device IN endpoints common interrupt mask register (OTG_FS_DIEPMSK) is available to enable/disable a single kind of endpoint interrupt source on all of the IN endpoints (EP0 included)
  • – Support for incomplete isochronous IN transfer interrupt (IISOIXFR bit in OTG_FS_GINTSTS), asserted when there is at least one isochronous IN endpoint

on which the transfer is not completed in the current frame. This interrupt is asserted along with the end of periodic frame interrupt (OTG_FS_GINTSTS/EOPF).

• • 3 OUT endpoints
  • – Each of them can be configured to support the isochronous, bulk or interrupt transfer type
  • – Each of them has a proper control (OTG_FS_DOEPCTLx), transfer configuration (OTG_FS_DOEPTSIZx) and status-interrupt (OTG_FS_DOEPINTx) register
  • – Device Out endpoints common interrupt mask register (OTG_FS_DOEPMSK) is available to enable/disable a single kind of endpoint interrupt source on all of the OUT endpoints (EP0 included)
  • – Support for incomplete isochronous OUT transfer interrupt (INCOMPISOOUT bit in OTG_FS_GINTSTS), asserted when there is at least one isochronous OUT endpoint on which the transfer is not completed in the current frame. This interrupt is asserted along with the end of periodic frame interrupt (OTG_FS_GINTSTS/EOPF).

Endpoint control

• • The following endpoint controls are available to the application through the device endpoint-x IN/OUT control register (DIEPCTLx/DOEPCTLx):
  • – Endpoint enable/disable
  • – Endpoint activate in current configuration
  • – Program USB transfer type (isochronous, bulk, interrupt)
  • – Program supported packet size
  • – Program Tx-FIFO number associated with the IN endpoint
  • – Program the expected or transmitted data0/data1 PID (bulk/interrupt only)
  • – Program the even/odd frame during which the transaction is received or transmitted (isochronous only)
  • – Optionally program the NAK bit to always negative-acknowledge the host regardless of the FIFO status
  • – Optionally program the STALL bit to always stall host tokens to that endpoint
  • – Optionally program the SNOOP mode for OUT endpoint not to check the CRC field of received data

Endpoint transfer

The device endpoint-x transfer size registers (DIEPTSIZx/DOEPTSIZx) allow the application to program the transfer size parameters and read the transfer status. Programming must be done before setting the endpoint enable bit in the endpoint control register. Once the endpoint is enabled, these fields are read-only as the OTG FS core updates them with the current transfer status.

The following transfer parameters can be programmed:

• • Transfer size in bytes
• • Number of packets that constitute the overall transfer size

Endpoint status/interrupt

The device endpoint-x interrupt registers (DIEPINTx/DOEPINTx) indicate the status of an endpoint with respect to USB- and AHB-related events. The application must read these registers when the OUT endpoint interrupt bit or the IN endpoint interrupt bit in the core interrupt register (OEPINT bit in OTG_FS_GINTSTS or IEPINT bit in OTG_FS_GINTSTS, respectively) is set. Before the application can read these registers, it must first read the device all endpoints interrupt (OTG_FS_DAINT) register to get the exact endpoint number for the device endpoint-x interrupt register. The application must clear the appropriate bit in this register to clear the corresponding bits in the DAINT and GINTSTS registers

The peripheral core provides the following status checks and interrupt generation:

• • Transfer completed interrupt, indicating that data transfer was completed on both the application (AHB) and USB sides
• • Setup stage has been done (control-out only)
• • Associated transmit FIFO is half or completely empty (in endpoints)
• • NAK acknowledge has been transmitted to the host (isochronous-in only)
• • IN token received when Tx-FIFO was empty (bulk-in/interrupt-in only)
• • Out token received when endpoint was not yet enabled
• • Babble error condition has been detected
• • Endpoint disable by application is effective
• • Endpoint NAK by application is effective (isochronous-in only)
• • More than 3 back-to-back setup packets were received (control-out only)
• • Timeout condition detected (control-in only)
• • Isochronous out packet has been dropped, without generating an interrupt

22.6 USB host

This section gives the functional description of the OTG_FS in the USB host mode. The OTG_FS works as a USB host in the following circumstances:

• • OTG A-host
  • – OTG A-device default state when the A-side of the USB cable is plugged in
• • OTG B-host
  • – OTG B-device after HNP switching to the host role
• • A-device
  • – If the ID line is present, functional and connected to the A-side of the USB cable, and the HNP-capable bit is cleared in the Global USB Configuration register (HNP CAP bit in OTG_FS_GUSBCFG). Integrated pull-down resistors are automatically set on the DP/DM lines.
• • Host only (see Figure 245: USB host-only connection ).
  • – The force host mode bit in the global USB configuration register (FHMOD bit in OTG_FS_GUSBCFG) forces the OTG_FS core to work as a USB host-only. In this case, the ID line is ignored even if present on the USB connector. Integrated pull-down resistors are automatically set on the DP/DM lines.

Note: On-chip 5 V \( V_{BUS} \) generation is not supported. For this reason, a charge pump or, if 5 V are available on the application board, a basic power switch must be added externally to drive

the 5 V \( V_{BUS} \) line. The external charge pump can be driven by any GPIO output. This is required for the OTG A-host, A-device and host-only configurations.

The \( V_{BUS} \) input ensures that valid \( V_{BUS} \) levels are supplied by the charge pump during USB operations while the charge pump overcurrent output can be input to any GPIO pin configured to generate port interrupts. The overcurrent ISR must promptly disable the \( V_{BUS} \) generation.

Figure 245. USB host-only connection

graph LR
    subgraph MCU [STM32 Microcontroller]
        VDD
        GPIO
        GPIO_IRQ[GPIO + IRQ]
        OSC_IN
        OSC_OUT
        DM_MCU[DM]
        DP_MCU[DP]
    end
    
    subgraph Switch [STMP2141STR Switch]
        EN
        OC[Overcurrent]
        PWR_IN[5 V]
        PWR_OUT[5 V Pwr]
    end
    
    subgraph USB [USB Std-A connector]
        VBUS
        DM_USB[DM]
        DP_USB[DP]
        VSS
    end

    VDD --- 5V_Source[VDD]
    GPIO --> EN
    OC --> GPIO_IRQ
    PWR_IN --- 5V_Source2[5 V]
    PWR_OUT --> VBUS
    DM_MCU <--> DM_USB
    DP_MCU <--> DP_USB
    OSC_IN --- Crystal
    OSC_OUT --- Crystal
    VSS --- GND[Ground]

1. 1. STMP2141STR needed only if the application has to support a \( V_{BUS} \) powered device. A basic power switch can be used if 5 V are available on the application board.
2. 2. \( V_{DD} \) range is between 2 V and 3.6 V.

22.6.1 SRP-capable host

SRP support is available through the SRP capable bit in the global USB configuration register (SRPCAP bit in OTG_FS_GUSBCFG). With the SRP feature enabled, the host can save power by switching off the \( V_{BUS} \) power while the USB session is suspended.

The SRP host mode program model is described in detail in the A-device session request protocol section.

22.6.2 USB host states

Host port power

On-chip 5 V \( V_{BUS} \) generation is not supported. For this reason, a charge pump or, if 5 V are available on the application board, a basic power switch, must be added externally to drive the 5 V \( V_{BUS} \) line. The external charge pump can be driven by any GPIO output. When the application decides to power on \( V_{BUS} \) using the chosen GPIO, it must also set the port power bit in the host port control and status register (PPWR bit in OTG_FS_HPRT).

\( V_{BUS} \) valid

When HNP or SRP is enabled the VBUS sensing pin (PA9) pin should be connected to \( V_{BUS} \) . The \( V_{BUS} \) input ensures that valid \( V_{BUS} \) levels are supplied by the charge pump during USB operations. Any unforeseen \( V_{BUS} \) voltage drop below the \( V_{BUS} \) valid threshold (4.25 V) leads to an OTG interrupt triggered by the session end detected bit (SEDET bit in

OTG_FS_GOTGINT). The application is then required to remove the \( V_{BUS} \) power and clear the port power bit.

When HNP and SRP are both disabled, the VBUS sensing pin (PA9) should not be connected to \( V_{BUS} \) . This pin can be used as GPIO.

The charge pump overcurrent flag can also be used to prevent electrical damage. Connect the overcurrent flag output from the charge pump to any GPIO input and configure it to generate a port interrupt on the active level. The overcurrent ISR must promptly disable the \( V_{BUS} \) generation and clear the port power bit.

Host detection of a peripheral connection

If SRP or HNP are enabled, even if USB peripherals or B-devices can be attached at any time, the OTG_FS does not detect any bus connection. When \( V_{BUS} \) is at a valid level and a remote B-device is attached, the OTG_FS core issues a host port interrupt triggered by the device connected bit in the host port control and status register (PCDET bit in OTG_FS_HPRT).

When HNP and SRP are both disabled, USB peripherals or B-device are detected as soon as they are connected. The OTG_FS core issues a host port interrupt triggered by the device connected bit in the host port control and status (PCDET bit in OTG_FS_HPRT).

Host detection of peripheral a disconnection

The peripheral disconnection event triggers the disconnect detected interrupt (DISCINT bit in OTG_FS_GINTSTS).

Host enumeration

After detecting a peripheral connection the host must start the enumeration process by sending USB reset and configuration commands to the new peripheral.

Before starting to drive a USB reset, the application waits for the OTG interrupt triggered by the debounce done bit (DBCDNE bit in OTG_FS_GOTGINT), which indicates that the bus is stable again after the electrical debounce caused by the attachment of a pull-up resistor on DP (FS) or DM (LS).

The application drives a USB reset signaling (single-ended zero) over the USB by keeping the port reset bit set in the host port control and status register (PRST bit in OTG_FS_HPRT) for a minimum of 10 ms and a maximum of 20 ms. The application takes care of the timing count and then of clearing the port reset bit.

Once the USB reset sequence has completed, the host port interrupt is triggered by the port enable/disable change bit (PENCHNG bit in OTG_FS_HPRT). This informs the application that the speed of the enumerated peripheral can be read from the port speed field in the host port control and status register (PSPD bit in OTG_FS_HPRT) and that the host is starting to drive SOFs (FS) or Keep alives (LS). The host is now ready to complete the peripheral enumeration by sending peripheral configuration commands.

Host suspend

The application decides to suspend the USB activity by setting the port suspend bit in the host port control and status register (PSUSP bit in OTG_FS_HPRT). The OTG_FS core stops sending SOFs and enters the suspended state.

The suspended state can be optionally exited on the remote device's initiative (remote wake-up). In this case the remote wake-up interrupt (WKUPINT bit in OTG_FS_GINTSTS)

is generated upon detection of a remote wake-up signaling, the port resume bit in the host port control and status register (PRES bit in OTG_FS_HPRT) self-sets, and resume signaling is automatically driven over the USB. The application must time the resume window and then clear the port resume bit to exit the suspended state and restart the SOF.

If the suspended state is exited on the host initiative, the application must set the port resume bit to start resume signaling on the host port, time the resume window and finally clear the port resume bit.

22.6.3 Host channels

The OTG_FS core instantiates 8 host channels. Each host channel supports an USB host transfer (USB pipe). The host is not able to support more than 8 transfer requests at the same time. If more than 8 transfer requests are pending from the application, the host controller driver (HCD) must re-allocate channels when they become available from previous duty, that is, after receiving the transfer completed and channel halted interrupts.

Each host channel can be configured to support in/out and any type of periodic/nonperiodic transaction. Each host channel makes use of proper control (HCCHARx), transfer configuration (HCTSIZx) and status/interrupt (HCINTx) registers with associated mask (HCINTMSKx) registers.

Host channel control

• • The following host channel controls are available to the application through the host channel-x characteristics register (HCCHARx):
  • – Channel enable/disable
  • – Program the FS/LS speed of target USB peripheral
  • – Program the address of target USB peripheral
  • – Program the endpoint number of target USB peripheral
  • – Program the transfer IN/OUT direction
  • – Program the USB transfer type (control, bulk, interrupt, isochronous)
  • – Program the maximum packet size (MPS)
  • – Program the periodic transfer to be executed during odd/even frames

Host channel transfer

The host channel transfer size registers (HCTSIZx) allow the application to program the transfer size parameters, and read the transfer status. Programming must be done before setting the channel enable bit in the host channel characteristics register. Once the endpoint is enabled the packet count field is read-only as the OTG_FS core updates it according to the current transfer status.

• • The following transfer parameters can be programmed:
  • – transfer size in bytes
  • – number of packets making up the overall transfer size
  • – initial data PID

Host channel status/interrupt

The host channel-x interrupt register (HCINTx) indicates the status of an endpoint with respect to USB- and AHB-related events. The application must read these registers when the host channels interrupt bit in the core interrupt register (HCINT bit in OTG_FS_GINTSTS) is

set. Before the application can read these registers, it must first read the host all channels interrupt (HCAINT) register to get the exact channel number for the host channel-x interrupt register. The application must clear the appropriate bit in this register to clear the corresponding bits in the HAINT and GINTSTS registers. The mask bits for each interrupt source of each channel are also available in the OTG_FS_HCINTMSK-x register.

• • The host core provides the following status checks and interrupt generation:
  • – Transfer completed interrupt, indicating that the data transfer is complete on both the application (AHB) and USB sides
  • – Channel has stopped due to transfer completed, USB transaction error or disable command from the application
  • – Associated transmit FIFO is half or completely empty (IN endpoints)
  • – ACK response received
  • – NAK response received
  • – STALL response received
  • – USB transaction error due to CRC failure, timeout, bit stuff error, false EOP
  • – Babble error
  • – fraMe overrun
  • – dAta toggle error

22.6.4 Host scheduler

The host core features a built-in hardware scheduler which is able to autonomously re-order and manage the USB transaction requests posted by the application. At the beginning of each frame the host executes the periodic (isochronous and interrupt) transactions first, followed by the nonperiodic (control and bulk) transactions to achieve the higher level of priority granted to the isochronous and interrupt transfer types by the USB specification.

The host processes the USB transactions through request queues (one for periodic and one for nonperiodic). Each request queue can hold up to 8 entries. Each entry represents a pending transaction request from the application, and holds the IN or OUT channel number along with other information to perform a transaction on the USB. The order in which the requests are written to the queue determines the sequence of the transactions on the USB interface.

At the beginning of each frame, the host processes the periodic request queue first, followed by the nonperiodic request queue. The host issues an incomplete periodic transfer interrupt (IPXFR bit in OTG_FS_GINTSTS) if an isochronous or interrupt transaction scheduled for the current frame is still pending at the end of the current frame. The OTG HS core is fully responsible for the management of the periodic and nonperiodic request queues. The periodic transmit FIFO and queue status register (HPTXSTS) and nonperiodic transmit FIFO and queue status register (HNPTXSTS) are read-only registers which can be used by the application to read the status of each request queue. They contain:

• • The number of free entries currently available in the periodic (nonperiodic) request queue (8 max)
• • Free space currently available in the periodic (nonperiodic) Tx-FIFO (out-transactions)
• • IN/OUT token, host channel number and other status information.

As request queues can hold a maximum of 8 entries each, the application can push to schedule host transactions in advance with respect to the moment they physically reach the

SB for a maximum of 8 pending periodic transactions plus 8 pending nonperiodic transactions.

To post a transaction request to the host scheduler (queue) the application must check that there is at least 1 entry available in the periodic (nonperiodic) request queue by reading the PTXQSAV bits in the OTG_FS_HNPTXSTS register or NPTQXSAV bits in the OTG_FS_HNPTXSTS register.

22.7 SOF trigger

Figure 246. SOF connectivity

The OTG FS core provides means to monitor, track and configure SOF framing in the host and peripheral, as well as an SOF pulse output connectivity feature.

Such utilities are especially useful for adaptive audio clock generation techniques, where the audio peripheral needs to synchronize to the isochronous stream provided by the PC, or the host needs to trim its framing rate according to the requirements of the audio peripheral.

22.7.1 Host SOFs

In host mode the number of PHY clocks occurring between the generation of two consecutive SOF (FS) or Keep-alive (LS) tokens is programmable in the host frame interval register (HFIR), thus providing application control over the SOF framing period. An interrupt is generated at any start of frame (SOF bit in OTH_FS_GINTSTS). The current frame number and the time remaining until the next SOF are tracked in the host frame number register (HFNUM).

An SOF pulse signal, generated at any SOF starting token and with a width of 20 HCLK cycles, can be made available externally on the OTG_FS_SOF pin using the SOFOUTEN bit in the global control and configuration register. The SOF pulse is also internally connected to the input trigger of timer 2 (TIM2), so that the input capture feature, the output compare feature and the timer can be triggered by the SOF pulse. The TIM2 connection is enabled register.

22.7.2 Peripheral SOFs

In device mode, the start of frame interrupt is generated each time an SOF token is received on the USB (SOF bit in OTH_FS_GINTSTS). The corresponding frame number can be read from the device status register (FNSOF bit in OTG_FS_DSTS). An SOF pulse signal with a width of 20 HCLK cycles is also generated and can be made available externally on the OTG_FS_SOF pin by using the SOF output enable bit in the global control and configuration register (SOFOUTEN bit in OTG_FS_GCCFG). The SOF pulse signal is also internally connected to the TIM2 input trigger, so that the input capture feature, the output compare feature and the timer can be triggered by the SOF pulse. The TIM2 connection is enabled .

The end of periodic frame interrupt (GINTSTS/EOPF) is used to notify the application when 80%, 85%, 90% or 95% of the time frame interval elapsed depending on the periodic frame interval field in the device configuration register (PFIVL bit in OTG_FS_DCFG). This feature can be used to determine if all of the isochronous traffic for that frame is complete.

22.8 OTG low-power modes

Table 127 below defines the STM32 low power modes and their compatibility with the OTG.

Table 127. Compatibility of STM32 low power modes with the OTG

1. 1. Within Stop mode there are different possible settings. Some restrictions may also exist, please refer to Section 5: Power controller (PWR) to understand which (if any) restrictions apply when using OTG.

The power consumption of the OTG PHY is controlled by three bits in the general core configuration register:

• • PHY power down (GCCFG/PWRDWN)
  It switches on/off the full-speed transceiver module of the PHY. It must be preliminarily set to allow any USB operation.
• • A-V _BUS sensing enable (GCCFG/VBUSASEN)
  It switches on/off the V _BUS comparators associated with A-device operations. It must be set when in A-device (USB host) mode and during HNP.
• • B-V _BUS sensing enable (GCCFG/VBUSASEN)
  It switches on/off the V _BUS comparators associated with B-device operations. It must be set when in B-device (USB peripheral) mode and during HNP.

Power reduction techniques are available while in the USB suspended state, when the USB session is not yet valid or the device is disconnected.

• • Stop PHY clock (STPPCLK bit in OTG_FS_PCGCTL)

When setting the stop PHY clock bit in the clock gating control register, most of the 48 MHz clock domain internal to the OTG full-speed core is switched off by clock gating. The dynamic power consumption due to the USB clock switching activity is cut even if the 48 MHz clock input is kept running by the application

Most of the transceiver is also disabled, and only the part in charge of detecting the asynchronous resume or remote wake-up event is kept alive.

• • Gate HCLK (GATEHCLK bit in OTG_FS_PCGCTL)

When setting the Gate HCLK bit in the clock gating control register, most of the system clock domain internal to the OTG_FS core is switched off by clock gating. Only the register read and write interface is kept alive. The dynamic power consumption due to the USB clock switching activity is cut even if the system clock is kept running by the application for other purposes.

• • USB system stop

When the OTG_FS is in the USB suspended state, the application may decide to drastically reduce the overall power consumption by a complete shut down of all the clock sources in the system. USB System Stop is activated by first setting the Stop PHY clock bit and then configuring the system deep sleep mode in the power control system module (PWR).

The OTG_FS core automatically reactivates both system and USB clocks by asynchronous detection of remote wake-up (as an host) or resume (as a device) signaling on the USB.

To save dynamic power, the USB data FIFO is clocked only when accessed by the OTG_FS core.

22.9 Dynamic update of the OTG_FS_HFIR register

The USB core embeds a dynamic trimming capability of SOF framing period in host mode allowing to synchronize an external device with the SOF frames.

When the OTG_FS_HFIR register is changed within a current SOF frame, the SOF period correction is applied in the next frame as described in Figure 247 .

Figure 247. Updating OTG_FS_HFIR dynamically

22.10 USB data FIFOs

The USB system features 1.25 Kbyte of dedicated RAM with a sophisticated FIFO control mechanism. The packet FIFO controller module in the OTG_FS core organizes RAM space into Tx-FIFOs into which the application pushes the data to be temporarily stored before the USB transmission, and into a single Rx FIFO where the data received from the USB are temporarily stored before retrieval (popped) by the application. The number of instructed FIFOs and how these are organized inside the RAM depends on the device's role. In peripheral mode an additional Tx-FIFO is instructed for each active IN endpoint. Any FIFO size is software configured to better meet the application requirements.

22.11 Peripheral FIFO architecture

Figure 248. Device-mode FIFO address mapping and AHB FIFO access mapping

22.11.1 Peripheral Rx FIFO

The OTG peripheral uses a single receive FIFO that receives the data directed to all OUT endpoints. Received packets are stacked back-to-back until free space is available in the Rx-FIFO. The status of the received packet (which contains the OUT endpoint destination number, the byte count, the data PID and the validity of the received data) is also stored by the core on top of the data payload. When no more space is available, host transactions are NACKed and an interrupt is received on the addressed endpoint. The size of the receive FIFO is configured in the receive FIFO Size register (GRXFSIZ).

The single receive FIFO architecture makes it more efficient for the USB peripheral to fill in the receive RAM buffer:

• • All OUT endpoints share the same RAM buffer (shared FIFO)
• • The OTG FS core can fill in the receive FIFO up to the limit for any host sequence of OUT tokens

The application keeps receiving the Rx-FIFO non-empty interrupt (RXFLVL bit in OTG_FS_GINTSTS) as long as there is at least one packet available for download. It reads the packet information from the receive status read and pop register (GRXSTSP) and finally pops data off the receive FIFO by reading from the endpoint-related pop address.

22.11.2 Peripheral Tx FIFOs

The core has a dedicated FIFO for each IN endpoint. The application configures FIFO sizes by writing the non periodic transmit FIFO size register (OTG_FS_TX0FSIZ) for IN endpoint0 and the device IN endpoint transmit FIFOx registers (DIEPTXFx) for IN endpoint-x.

22.12 Host FIFO architecture

Figure 249. Host-mode FIFO address mapping and AHB FIFO access mapping

22.12.1 Host Rx FIFO

The host uses one receiver FIFO for all periodic and nonperiodic transactions. The FIFO is used as a receive buffer to hold the received data (payload of the received packet) from the USB until it is transferred to the system memory. Packets received from any remote IN endpoint are stacked back-to-back until free space is available. The status of each received packet with the host channel destination, byte count, data PID and validity of the received data are also stored into the FIFO. The size of the receive FIFO is configured in the receive FIFO size register (GRXFSIZ).

The single receive FIFO architecture makes it highly efficient for the USB host to fill in the receive data buffer:

• • All IN configured host channels share the same RAM buffer (shared FIFO)
• • The OTG_FS core can fill in the receive FIFO up to the limit for any sequence of IN tokens driven by the host software

The application receives the Rx FIFO not-empty interrupt as long as there is at least one packet available for download. It reads the packet information from the receive status read and pop register and finally pops the data off the receive FIFO.

22.12.2 Host Tx FIFOs

The host uses one transmit FIFO for all non-periodic (control and bulk) OUT transactions and one transmit FIFO for all periodic (isochronous and interrupt) OUT transactions. FIFOs are used as transmit buffers to hold the data (payload of the transmit packet) to be transmitted over the USB. The size of the periodic (nonperiodic) Tx FIFO is configured in the host periodic (nonperiodic) transmit FIFO size (HPTXFSIZ/HNPTXFSIZ) register.

The two Tx FIFO implementation derives from the higher priority granted to the periodic type of traffic over the USB frame. At the beginning of each frame, the built-in host scheduler processes the periodic request queue first, followed by the nonperiodic request queue.

The two transmit FIFO architecture provides the USB host with separate optimization for periodic and nonperiodic transmit data buffer management:

• • All host channels configured to support periodic (nonperiodic) transactions in the OUT direction share the same RAM buffer (shared FIFOs)
• • The OTG_FS core can fill in the periodic (nonperiodic) transmit FIFO up to the limit for any sequence of OUT tokens driven by the host software

The OTG_FS core issues the periodic Tx FIFO empty interrupt (PTXFE bit in OTG_FS_GINTSTS) as long as the periodic Tx-FIFO is half or completely empty, depending on the value of the periodic Tx-FIFO empty level bit in the AHB configuration register (PTXFELVL bit in OTG_FS_GAHBCFG). The application can push the transmission data in advance as long as free space is available in both the periodic Tx FIFO and the periodic request queue. The host periodic transmit FIFO and queue status register (HPTXSTS) can be read to know how much space is available in both.

OTG_FS core issues the non periodic Tx FIFO empty interrupt (NPTXFE bit in OTG_FS_GINTSTS) as long as the nonperiodic Tx FIFO is half or completely empty depending on the non periodic Tx FIFO empty level bit in the AHB configuration register (TXFELVL bit in OTG_FS_GAHBCFG). The application can push the transmission data as long as free space is available in both the nonperiodic Tx FIFO and nonperiodic request queue. The host nonperiodic transmit FIFO and queue status register (HNPTXSTS) can be read to know how much space is available in both.

22.13 FIFO RAM allocation

22.13.1 Device mode

Receive FIFO RAM allocation: the application should allocate RAM for SETUP Packets: 10 locations must be reserved in the receive FIFO to receive SETUP packets on control endpoint. The core does not use these locations, which are reserved for SETUP packets, to write any other data. One location is to be allocated for Global OUT NAK. Status information is written to the FIFO along with each received packet. Therefore, a minimum space of \( (\text{Largest Packet Size} / 4) + 1 \) must be allocated to receive packets. If multiple isochronous endpoints are enabled, then at least two \( (\text{Largest Packet Size} / 4) + 1 \) spaces must be allocated to receive back-to-back packets. Typically, two \( (\text{Largest Packet Size} / 4) + 1 \) spaces are recommended so that when the previous packet is being transferred to the CPU, the USB can receive the subsequent packet.

Along with the last packet for each endpoint, transfer complete status information is also pushed to the FIFO. Typically, one location for each OUT endpoint is recommended.

Transmit FIFO RAM allocation: the minimum RAM space required for each IN Endpoint Transmit FIFO is the maximum packet size for that particular IN endpoint.

Note: More space allocated in the transmit IN Endpoint FIFO results in better performance on the USB.

22.13.2 Host mode

Receive FIFO RAM allocation

Status information is written to the FIFO along with each received packet. Therefore, a minimum space of \( (\text{Largest Packet Size} / 4) + 1 \) must be allocated to receive packets. If multiple isochronous channels are enabled, then at least two \( (\text{Largest Packet Size} / 4) + 1 \) spaces must be allocated to receive back-to-back packets. Typically, two \( (\text{Largest Packet Size} / 4) + 1 \) spaces are recommended so that when the previous packet is being transferred to the CPU, the USB can receive the subsequent packet.

Along with the last packet in the host channel, transfer complete status information is also pushed to the FIFO. So one location must be allocated for this.

Transmit FIFO RAM allocation

The minimum amount of RAM required for the host Non-periodic Transmit FIFO is the largest maximum packet size among all supported non-periodic OUT channels.

Typically, two Largest Packet Sizes worth of space is recommended, so that when the current packet is under transfer to the USB, the CPU can get the next packet.

The minimum amount of RAM required for host periodic Transmit FIFO is the largest maximum packet size out of all the supported periodic OUT channels. If there is at least one Isochronous OUT endpoint, then the space must be at least two times the maximum packet size of that channel.

Note: More space allocated in the Transmit Non-periodic FIFO results in better performance on the USB.

22.14 USB system performance

Best USB and system performance is achieved owing to the large RAM buffers, the highly configurable FIFO sizes, the quick 32-bit FIFO access through AHB push/pop registers and, especially, the advanced FIFO control mechanism. Indeed, this mechanism allows the OTG_FS to fill in the available RAM space at best regardless of the current USB sequence. With these features:

• • The application gains good margins to calibrate its intervention in order to optimize the CPU bandwidth usage:
  • – It can accumulate large amounts of transmission data in advance compared to when they are effectively sent over the USB
  • – It benefits of a large time margin to download data from the single receive FIFO
• • The USB Core is able to maintain its full operating rate, that is to provide maximum full-speed bandwidth with a great margin of autonomy versus application intervention:
  • – It has a large reserve of transmission data at its disposal to autonomously manage the sending of data over the USB

• – It has a lot of empty space available in the receive buffer to autonomously fill it in with the data coming from the USB

As the OTG_FS core is able to fill in the 1.25 Kbyte RAM buffer very efficiently, and as 1.25 Kbyte of transmit/receive data is more than enough to cover a full speed frame, the USB system is able to withstand the maximum full-speed data rate for up to one USB frame (1 ms) without any CPU intervention.

22.15 OTG_FS interrupts

When the OTG_FS controller is operating in one mode, either device or host, the application must not access registers from the other mode. If an illegal access occurs, a mode mismatch interrupt is generated and reflected in the Core interrupt register (MMIS bit in the OTG_FS_GINTSTS register). When the core switches from one mode to the other, the registers in the new mode of operation must be reprogrammed as they would be after a power-on reset.

Figure 250 shows the interrupt hierarchy.

Figure 250. Interrupt hierarchy

1. 1. OTG_FS_WKUP become active (high state) when resume condition occurs during L1 SLEEP or L2 SUSPEND states.

22.16 OTG_FS control and status registers

By reading from and writing to the control and status registers (CSRs) through the AHB slave interface, the application controls the OTG_FS controller. These registers are 32 bits wide, and the addresses are 32-bit block aligned. The OTG_FS registers must be accessed by words (32 bits).

CSRs are classified as follows:

• • Core global registers
• • Host-mode registers
• • Host global registers
• • Host port CSRs
• • Host channel-specific registers
• • Device-mode registers
• • Device global registers
• • Device endpoint-specific registers
• • Power and clock-gating registers
• • Data FIFO (DFIFO) access registers

Only the Core global, Power and clock-gating, Data FIFO access, and host port control and status registers can be accessed in both host and device modes. When the OTG_FS controller is operating in one mode, either device or host, the application must not access registers from the other mode. If an illegal access occurs, a mode mismatch interrupt is generated and reflected in the Core interrupt register (MMIS bit in the OTG_FS_GINTSTS register). When the core switches from one mode to the other, the registers in the new mode of operation must be reprogrammed as they would be after a power-on reset.

22.16.1 CSR memory map

The host and device mode registers occupy different addresses. All registers are implemented in the AHB clock domain.

Figure 251. CSR memory map

1. x = 3 in device mode and x = 7 in host mode.

Global CSR map

These registers are available in both host and device modes.

Table 128. Core global control and status registers (CSRs)

1. The general rule is to use OTG_FS_HNPTXFSIZ for host mode and OTG_FS_DIEPTXF0 for device mode.

Host-mode CSR map

These registers must be programmed every time the core changes to host mode.

These registers must be programmed every time the core changes to device mode.

Table 130. Device-mode control and status registers (continued)

Data FIFO (DFIFO) access register map

These registers, available in both host and device modes, are used to read or write the FIFO space for a specific endpoint or a channel, in a given direction. If a host channel is of type IN, the FIFO can only be read on the channel. Similarly, if a host channel is of type OUT, the FIFO can only be written on the channel.

Table 131. Data FIFO (DFIFO) access register map

1. Where x is 3 in device mode and 7 in host mode.

Power and clock gating CSR map

There is a single register for power and clock gating. It is available in both host and device modes.

22.16.2 OTG_FS global registers

These registers are available in both host and device modes, and do not need to be reprogrammed when switching between these modes.

Bit values in the register descriptions are expressed in binary unless otherwise specified.

OTG_FS control and status register (OTG_FS_GOTGCTL)

Address offset: 0x000

Reset value: 0x0001 0000

The OTG_FS_GOTGCTL register controls the behavior and reflects the status of the OTG function of the core.

Bits 31:20 Reserved, must be kept at reset value.

Bit 19 BSVLD : B-session valid

Indicates the device mode transceiver status.

0: B-session is not valid.

1: B-session is valid.

In OTG mode, you can use this bit to determine if the device is connected or disconnected.

Note: Only accessible in device mode.

Bit 18 ASVLD : A-session valid

Indicates the host mode transceiver status.

0: A-session is not valid

1: A-session is valid

Note: Only accessible in host mode.

Bit 17 DBCT : Long/short debounce time

Indicates the debounce time of a detected connection.

0: Long debounce time, used for physical connections (100 ms + 2.5 µs)

1: Short debounce time, used for soft connections (2.5 µs)

Note: Only accessible in host mode.

Bit 16 CIDSTS : Connector ID status

Indicates the connector ID status on a connect event.

0: The OTG_FS controller is in A-device mode

1: The OTG_FS controller is in B-device mode

Note: Accessible in both device and host modes.

Bits 15:12 Reserved, must be kept at reset value.

The application sets this bit when it successfully receives a SetFeature.SetHNPEnable command from the connected USB host.

0: HNP is not enabled in the application

1: HNP is enabled in the application

Note: Only accessible in device mode.

The application sets this bit when it has successfully enabled HNP (using the SetFeature.SetHNPEnable command) on the connected device.

0: Host Set HNP is not enabled

1: Host Set HNP is enabled

Note: Only accessible in host mode.

The application sets this bit to initiate an HNP request to the connected USB host. The application can clear this bit by writing a 0 when the host negotiation success status change bit in the OTG_FS_GOTGINT register (HNSSCHG bit in OTG_FS_GOTGINT) is set. The core clears this bit when the HNSSCHG bit is cleared.

0: No HNP request

1: HNP request

Note: Only accessible in device mode.

The core sets this bit when host negotiation is successful. The core clears this bit when the HNP Request (HNPRQ) bit in this register is set.

0: Host negotiation failure

1: Host negotiation success

Note: Only accessible in device mode.

Bits 7:2 Reserved, must be kept at reset value.

The application sets this bit to initiate a session request on the USB. The application can clear this bit by writing a 0 when the host negotiation success status change bit in the OTG_FS_GOTGINT register (HNSSCHG bit in OTG_FS_GOTGINT) is set. The core clears this bit when the HNSSCHG bit is cleared.

If you use the USB 1.1 full-speed serial transceiver interface to initiate the session request, the application must wait until \( V_{BUS} \) discharges to 0.2 V, after the B-Session Valid bit in this register (BSVLD bit in OTG_FS_GOTGCTL) is cleared.

0: No session request

1: Session request

Note: Only accessible in device mode.

The core sets this bit when a session request initiation is successful.

0: Session request failure

1: Session request success

Note: Only accessible in device mode.

Address offset: 0x04

Reset value: 0x0000 0000

The application reads this register whenever there is an OTG interrupt and clears the bits in this register to clear the OTG interrupt.

Bits 31:20 Reserved, must be kept at reset value.

Bit 19 DBCDNE : Debounce done

The core sets this bit when the debounce is completed after the device connect. The application can start driving USB reset after seeing this interrupt. This bit is only valid when the HNP Capable or SRP Capable bit is set in the OTG_FS_GUSBCFG register (HNPCAP bit or SRPCAP bit in OTG_FS_GUSBCFG, respectively).

Note: Only accessible in host mode.

Bit 18 ADTOCHG : A-device timeout change

The core sets this bit to indicate that the A-device has timed out while waiting for the B-device to connect.

Note: Accessible in both device and host modes.

Bit 17 HNGDET : Host negotiation detected

The core sets this bit when it detects a host negotiation request on the USB.

Note: Accessible in both device and host modes.

Bits 16:10 Reserved, must be kept at reset value.

Bit 9 HNSSCHG : Host negotiation success status change

The core sets this bit on the success or failure of a USB host negotiation request. The application must read the host negotiation success bit of the OTG_FS_GOTGCTL register (HNGSCS in OTG_FS_GOTGCTL) to check for success or failure.

Note: Accessible in both device and host modes.

Bits 7:3 Reserved, must be kept at reset value.

Bit 8 SRSSCHG : Session request success status change

The core sets this bit on the success or failure of a session request. The application must read the session request success bit in the OTG_FS_GOTGCTL register (SRQSCS bit in OTG_FS_GOTGCTL) to check for success or failure.

Note: Accessible in both device and host modes.

Bit 2 SEDET : Session end detected

The core sets this bit to indicate that the level of the voltage on V _BUS is no longer valid for a B-Peripheral session when V _BUS < 0.8 V.

Bits 1:0 Reserved, must be kept at reset value.

OTG_FS AHB configuration register (OTG_FS_GAHBCFG)

Address offset: 0x008

Reset value: 0x0000 0000

This register can be used to configure the core after power-on or a change in mode. This register mainly contains AHB system-related configuration parameters. Do not change this register after the initial programming. The application must program this register before starting any transactions on either the AHB or the USB.

Bits 31:9 Reserved, must be kept at reset value.

Bit 8 PTXFELVL: Periodic TxFIFO empty level

Indicates when the periodic TxFIFO empty interrupt bit in the OTG_FS_GINTSTS register (PTXFE bit in OTG_FS_GINTSTS) is triggered.

• 0: PTXFE (in OTG_FS_GINTSTS) interrupt indicates that the Periodic TxFIFO is half empty
• 1: PTXFE (in OTG_FS_GINTSTS) interrupt indicates that the Periodic TxFIFO is completely empty

Note: Only accessible in host mode.

Bit 7 TXFELVL: TxFIFO empty level

In device mode, this bit indicates when IN endpoint Transmit FIFO empty interrupt (TXFE in OTG_FS_DIEPINTx.) is triggered.

• 0: the TXFE (in OTG_FS_DIEPINTx) interrupt indicates that the IN Endpoint TxFIFO is half empty
• 1: the TXFE (in OTG_FS_DIEPINTx) interrupt indicates that the IN Endpoint TxFIFO is completely empty

In host mode, this bit indicates when the nonperiodic Tx FIFO empty interrupt (NPTXFE bit in OTG_FS_GINTSTS) is triggered:

• 0: the NPTXFE (in OTG_FS_GINTSTS) interrupt indicates that the nonperiodic Tx FIFO is half empty
• 1: the NPTXFE (in OTG_FS_GINTSTS) interrupt indicates that the nonperiodic Tx FIFO is completely empty

Bits 6:1 Reserved, must be kept at reset value.

Bit 0 GINTMSK: Global interrupt mask

The application uses this bit to mask or unmask the interrupt line assertion to itself. Irrespective of this bit's setting, the interrupt status registers are updated by the core.

• 0: Mask the interrupt assertion to the application.
• 1: Unmask the interrupt assertion to the application.

Note: Accessible in both device and host modes.

OTG_FS USB configuration register (OTG_FS_GUSBCFG)

Address offset: 0x00C

Reset value: 0x0000 1440

This register can be used to configure the core after power-on or a changing to host mode or device mode. It contains USB and USB-PHY related configuration parameters. The application must program this register before starting any transactions on either the AHB or the USB. Do not make changes to this register after the initial programming.

Bit 31 CTXPKT: Corrupt Tx packet

This bit is for debug purposes only. Never set this bit to 1.

Note: Accessible in both device and host modes.

Bit 30 FDMOD: Force device mode

Writing a 1 to this bit forces the core to device mode irrespective of the OTG_FS_ID input pin.

0: Normal mode

1: Force device mode

After setting the force bit, the application must wait at least 25 ms before the change takes effect.

Note: Accessible in both device and host modes.

Bit 29 FHMOD: Force host mode

Writing a 1 to this bit forces the core to host mode irrespective of the OTG_FS_ID input pin.

0: Normal mode

1: Force host mode

After setting the force bit, the application must wait at least 25 ms before the change takes effect.

Note: Accessible in both device and host modes.

Bits 28:14 Reserved, must be kept at reset value.

Bits 13:10 TRDT: USB turnaround time

These bits allow setting the turnaround time in PHY clocks. They must be configured according to Table 133: TRDT values , depending on the application AHB frequency. Higher TRDT values allow stretching the USB response time to IN tokens in order to compensate for longer AHB read access latency to the Data FIFO.

Note: Only accessible in device mode.

Bit 9 HNPCAP: HNP-capable

The application uses this bit to control the OTG_FS controller's HNP capabilities.

0: HNP capability is not enabled.

1: HNP capability is enabled.

Note: Accessible in both device and host modes.

Bit 8 SRPCAP : SRP-capable

The application uses this bit to control the OTG_FS controller's SRP capabilities. If the core operates as a non-SRP-capable

B-device, it cannot request the connected A-device (host) to activate V _BUS and start a session.

0: SRP capability is not enabled.

1: SRP capability is enabled.

Note: Accessible in both device and host modes.

Bit 7 Reserved, must be kept at reset value.

Bit 6 PHYSEL : Full speed serial transceiver select

This bit is always 1 with read-only access.

Bits 5:3 Reserved, must be kept at reset value.

Bits 2:0 TOCAL : FS timeout calibration

The number of PHY clocks that the application programs in this field is added to the full-speed interpacket timeout duration in the core to account for any additional delays introduced by the PHY. This can be required, because the delay introduced by the PHY in generating the line state condition can vary from one PHY to another.

The USB standard timeout value for full-speed operation is 16 to 18 (inclusive) bit times. The application must program this field based on the speed of enumeration. The number of bit times added per PHY clock is 0.25 bit times.

Table 133. TRDT values

Address offset: 0x010

Reset value: 0x8000 0000

The application uses this register to reset various hardware features inside the core.

Bit 31 AHBIDL : AHB master idle

Indicates that the AHB master state machine is in the Idle condition.

Note: Accessible in both device and host modes.

Bits 30:11 Reserved, must be kept at reset value.

Bits 10:6 TXFNUM : TxFIFO number

This is the FIFO number that must be flushed using the TxFIFO Flush bit. This field must not be changed until the core clears the TxFIFO Flush bit.

00000:

• – Non-periodic TxFIFO flush in host mode
• – Tx FIFO 0 flush in device mode

00001:

• – Periodic TxFIFO flush in host mode
• – TXFIFO 1 flush in device mode

00010: TXFIFO 2 flush in device mode

...

00101: TXFIFO 15 flush in device mode

10000: Flush all the transmit FIFOs in device or host mode.

Note: Accessible in both device and host modes.

Bit 5 TXFFLSH : TxFIFO flush

This bit selectively flushes a single or all transmit FIFOs, but cannot do so if the core is in the midst of a transaction.

The application must write this bit only after checking that the core is neither writing to the TxFIFO nor reading from the TxFIFO. Verify using these registers:

Read—NAK Effective Interrupt ensures the core is not reading from the FIFO

Write—AHBIDL bit in OTG_FS_GRSTCTL ensures the core is not writing anything to the FIFO.

Note: Accessible in both device and host modes.

Bit 4 RXFFLSH : RxFIFO flush

The application can flush the entire RxFIFO using this bit, but must first ensure that the core is not in the middle of a transaction.

The application must only write to this bit after checking that the core is neither reading from the RxFIFO nor writing to the RxFIFO.

The application must wait until the bit is cleared before performing any other operations. This bit requires 8 clocks (slowest of PHY or AHB clock) to clear.

Note: Accessible in both device and host modes.

Bit 3 Reserved, must be kept at reset value.

The application writes this bit to reset the frame number counter inside the core. When the frame counter is reset, the subsequent SOF sent out by the core has a frame number of 0.

Note: Only accessible in host mode.

The application uses this bit to flush the control logic in the AHB Clock domain. Only AHB Clock Domain pipelines are reset.

FIFOs are not flushed with this bit.

All state machines in the AHB clock domain are reset to the Idle state after terminating the transactions on the AHB, following the protocol.

CSR control bits used by the AHB clock domain state machines are cleared.

To clear this interrupt, status mask bits that control the interrupt status and are generated by the AHB clock domain state machine are cleared.

Because interrupt status bits are not cleared, the application can get the status of any core events that occurred after it set this bit.

This is a self-clearing bit that the core clears after all necessary logic is reset in the core. This can take several clocks, depending on the core's current state.

Note: Accessible in both device and host modes.

Resets the HCLK and PCLK domains as follows:

Clears the interrupts and all the CSR register bits except for the following bits:

• – RSTPDMODL bit in OTG_FS_PCGCCTL
• – GAYEHCLK bit in OTG_FS_PCGCCTL
• – PWRCLMP bit in OTG_FS_PCGCCTL
• – STPPCLK bit in OTG_FS_PCGCCTL
• – FSLSPCS bit in OTG_FS_HCFG
• – DSPD bit in OTG_FS_DCFG

All module state machines (except for the AHB slave unit) are reset to the Idle state, and all the transmit FIFOs and the receive FIFO are flushed.

Any transactions on the AHB Master are terminated as soon as possible, after completing the last data phase of an AHB transfer. Any transactions on the USB are terminated immediately.

The application can write to this bit any time it wants to reset the core. This is a self-clearing bit and the core clears this bit after all the necessary logic is reset in the core, which can take several clocks, depending on the current state of the core. Once this bit has been cleared, the software must wait at least 3 PHY clocks before accessing the PHY domain (synchronization delay). The software must also check that bit 31 in this register is set to 1 (AHB Master is Idle) before starting any operation.

Typically, the software reset is used during software development and also when you dynamically change the PHY selection bits in the above listed USB configuration registers. When you change the PHY, the corresponding clock for the PHY is selected and used in the PHY domain. Once a new clock is selected, the PHY domain has to be reset for proper operation.

Note: Accessible in both device and host modes.

OTG_FS core interrupt register (OTG_FS_GINTSTS)

Address offset: 0x014

Reset value: 0x0400 0020

This register interrupts the application for system-level events in the current mode (device mode or host mode).

Some of the bits in this register are valid only in host mode, while others are valid in device mode only. This register also indicates the current mode. To clear the interrupt status bits of the rc_w1 type, the application must write 1 into the bit.

The FIFO status interrupts are read-only; once software reads from or writes to the FIFO while servicing these interrupts, FIFO interrupt conditions are cleared automatically.

The application must clear the OTG_FS_GINTSTS register at initialization before unmasking the interrupt bit to avoid any interrupts generated prior to initialization.

Bit 31 WKUPINT : Resume/remote wake-up detected interrupt

In device mode, this interrupt is asserted when a resume is detected on the USB. In host mode, this interrupt is asserted when a remote wake-up is detected on the USB.

Note: Accessible in both device and host modes.

Bit 30 SRQINT : Session request/new session detected interrupt

In host mode, this interrupt is asserted when a session request is detected from the device. In device mode, this interrupt is asserted when V _BUS is in the valid range for a B-peripheral device. Accessible in both device and host modes.

Bit 29 DISCINT : Disconnect detected interrupt

Asserted when a device disconnect is detected.

Note: Only accessible in host mode.

Bit 28 CIDSCHG : Connector ID status change

The core sets this bit when there is a change in connector ID status.

Note: Accessible in both device and host modes.

Bit 27 Reserved, must be kept at reset value.

Bit 26 PTXFE : Periodic TxFIFO empty

Asserted when the periodic transmit FIFO is either half or completely empty and there is space for at least one entry to be written in the periodic request queue. The half or completely empty status is determined by the periodic TxFIFO empty level bit in the OTG_FS_GAHBCFG register (PTXFELVL bit in OTG_FS_GAHBCFG).

Note: Only accessible in host mode.

The core sets this bit to indicate that an interrupt is pending on one of the channels of the core (in host mode). The application must read the OTG_FS_HAINT register to determine the exact number of the channel on which the interrupt occurred, and then read the corresponding OTG_FS_HCINTx register to determine the exact cause of the interrupt. The application must clear the appropriate status bit in the OTG_FS_HCINTx register to clear this bit.

Note: Only accessible in host mode.

The core sets this bit to indicate a change in port status of one of the OTG_FS controller ports in host mode. The application must read the OTG_FS_HPRT register to determine the exact event that caused this interrupt. The application must clear the appropriate status bit in the OTG_FS_HPRT register to clear this bit.

Note: Only accessible in host mode.

Bits 23:22 Reserved, must be kept at reset value.

In host mode, the core sets this interrupt bit when there are incomplete periodic transactions still pending, which are scheduled for the current frame.

In device mode, the core sets this interrupt to indicate that there is at least one isochronous OUT endpoint on which the transfer is not completed in the current frame. This interrupt is asserted along with the End of periodic frame interrupt (EOPF) bit in this register.

The core sets this interrupt to indicate that there is at least one isochronous IN endpoint on which the transfer is not completed in the current frame. This interrupt is asserted along with the End of periodic frame interrupt (EOPF) bit in this register.

Note: Only accessible in device mode.

The core sets this bit to indicate that an interrupt is pending on one of the OUT endpoints of the core (in device mode). The application must read the OTG_FS_DAINT register to determine the exact number of the OUT endpoint on which the interrupt occurred, and then read the corresponding OTG_FS_DOEPINTx register to determine the exact cause of the interrupt. The application must clear the appropriate status bit in the corresponding OTG_FS_DOEPINTx register to clear this bit.

Note: Only accessible in device mode.

The core sets this bit to indicate that an interrupt is pending on one of the IN endpoints of the core (in device mode). The application must read the OTG_FS_DAINT register to determine the exact number of the IN endpoint on which the interrupt occurred, and then read the corresponding OTG_FS_DIEPINTx register to determine the exact cause of the interrupt.

The application must clear the appropriate status bit in the corresponding OTG_FS_DIEPINTx register to clear this bit.

Note: Only accessible in device mode.

Bits 17:16 Reserved, must be kept at reset value.

Indicates that the period specified in the periodic frame interval field of the OTG_FS_DCFG register (PFIVL bit in OTG_FS_DCFG) has been reached in the current frame.

Note: Only accessible in device mode.

The core sets this bit when it fails to write an isochronous OUT packet into the RxFIFO because the RxFIFO does not have enough space to accommodate a maximum size packet for the isochronous OUT endpoint.

Note: Only accessible in device mode.

The core sets this bit to indicate that speed enumeration is complete. The application must read the OTG_FS_DSTS register to obtain the enumerated speed.

Note: Only accessible in device mode.

The core sets this bit to indicate that a reset is detected on the USB.

Note: Only accessible in device mode.

The core sets this bit to indicate that a suspend was detected on the USB. The core enters the Suspended state when there is no activity on the data lines for a period of 3 ms.

Note: Only accessible in device mode.

The core sets this bit to indicate that an Idle state has been detected on the USB for 3 ms.

Note: Only accessible in device mode.

Bits 9:8 Reserved, must be kept at reset value.

Indicates that the Set global OUT NAK bit in the OTG_FS_DCTL register (SGONAK bit in OTG_FS_DCTL), set by the application, has taken effect in the core. This bit can be cleared by writing the Clear global OUT NAK bit in the OTG_FS_DCTL register (CGONAK bit in OTG_FS_DCTL).

Note: Only accessible in device mode.

Indicates that the Set global non-periodic IN NAK bit in the OTG_FS_DCTL register (SGINAK bit in OTG_FS_DCTL), set by the application, has taken effect in the core. That is, the core has sampled the Global IN NAK bit set by the application. This bit can be cleared by clearing the Clear global non-periodic IN NAK bit in the OTG_FS_DCTL register (CGINAK bit in OTG_FS_DCTL).

This interrupt does not necessarily mean that a NAK handshake is sent out on the USB. The STALL bit takes precedence over the NAK bit.

Note: Only accessible in device mode.

This interrupt is asserted when the non-periodic TxFIFO is either half or completely empty, and there is space for at least one entry to be written to the non-periodic transmit request queue. The half or completely empty status is determined by the non-periodic TxFIFO empty level bit in the OTG_FS_GAHBCFG register (TXFELVL bit in OTG_FS_GAHBCFG).

Note: Accessible in host mode only.

Indicates that there is at least one packet pending to be read from the RxFIFO.

Note: Accessible in both host and device modes.

In host mode, the core sets this bit to indicate that an SOF (FS), or Keep-Alive (LS) is transmitted on the USB. The application must write a 1 to this bit to clear the interrupt.

In device mode, in the core sets this bit to indicate that an SOF token has been received on the USB. The application can read the Device Status register to get the current frame number. This interrupt is seen only when the core is operating in FS.

Note: Accessible in both host and device modes.

The core sets this bit to indicate an OTG protocol event. The application must read the OTG Interrupt Status (OTG_FS_GOTGINT) register to determine the exact event that caused this interrupt. The application must clear the appropriate status bit in the OTG_FS_GOTGINT register to clear this bit.

Note: Accessible in both host and device modes.

The core sets this bit when the application is trying to access:

• – A host mode register, when the core is operating in device mode
• – A device mode register, when the core is operating in host mode

The register access is completed on the AHB with an OKAY response, but is ignored by the core internally and does not affect the operation of the core.

Note: Accessible in both host and device modes.

Indicates the current mode.

0: Device mode

1: Host mode

Note: Accessible in both host and device modes.

OTG_FS interrupt mask register (OTG_FS_GINTMSK)

Address offset: 0x018

Reset value: 0x0000 0000

This register works with the Core interrupt register to interrupt the application. When an interrupt bit is masked, the interrupt associated with that bit is not generated. However, the Core Interrupt (OTG_FS_GINTSTS) register bit corresponding to that interrupt is still set.

Bit 31 WUIM : Resume/remote wake-up detected interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both host and device modes.

Bit 30 SRQIM : Session request/new session detected interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both host and device modes.

Bit 29 DISCINT : Disconnect detected interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 28 CID SCHGM : Connector ID status change mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both host and device modes.

Bit 27 Reserved, must be kept at reset value.

Bit 26 PTXFEM : Periodic TxFIFO empty mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in host mode.

Bit 25 HCIM : Host channels interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in host mode.

Bit 24 PRTIM : Host port interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in host mode.

Bits 23:22 Reserved, must be kept at reset value.

Bit 21 IPXFRM : Incomplete periodic transfer mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in host mode.

IISOOXFRM : Incomplete isochronous OUT transfer mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 20 IISOIXFRM : Incomplete isochronous IN transfer mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 19 OEPINT : OUT endpoints interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 18 IEPINT : IN endpoints interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bits 17:16 Reserved, must be kept at reset value.

Bit 15 EOPFM : End of periodic frame interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 14 ISOODRPM : Isochronous OUT packet dropped interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 13 ENUMDNEM : Enumeration done mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 12 USBRST : USB reset mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 11 USBSUSPM : USB suspend mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 10 ESUSPM : Early suspend mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bits 9:8 Reserved, must be kept at reset value.

Bit 7 GONAKEFFM : Global OUT NAK effective mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 6 GINAKEFFM : Global non-periodic IN NAK effective mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in device mode.

Bit 5 NPTXFEM : Non-periodic TxFIFO empty mask

0: Masked interrupt

1: Unmasked interrupt

Note: Only accessible in Host mode.

Bit 4 RXFLVLM : Receive FIFO non-empty mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both device and host modes.

Bit 3 SOFM : Start of frame mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both device and host modes.

Bit 2 OTGINT : OTG interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both device and host modes.

Bit 1 MMISM : Mode mismatch interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Note: Accessible in both device and host modes.

Bit 0 Reserved, must be kept at reset value.

OTG_FS Receive status debug read/OTG status read and pop registers
(OTG_FS_GRXSTSR/OTG_FS_GRXSTSP)

Address offset for Read: 0x01C

Address offset for Pop: 0x020

Reset value: 0x0000 0000

A read to the Receive status debug read register returns the contents of the top of the Receive FIFO. A read to the Receive status read and pop register additionally pops the top data entry out of the RxFIFO.

The receive status contents must be interpreted differently in host and device modes. The core ignores the receive status pop/read when the receive FIFO is empty and returns a value of 0x0000 0000. The application must only pop the Receive Status FIFO when the Receive FIFO non-empty bit of the Core interrupt register (RXFLVL bit in OTG_FS_GINTSTS) is asserted.

Host mode

Bits 31:21 Reserved, must be kept at reset value.

Bits 20:17 PKTSTS : Packet status

Indicates the status of the received packet

0010: IN data packet received

0011: IN transfer completed (triggers an interrupt)

0101: Data toggle error (triggers an interrupt)

0111: Channel halted (triggers an interrupt)

Others: Reserved

Bits 16:15 DPID : Data PID

Indicates the Data PID of the received packet

00: DATA0

10: DATA1

01: DATA2

11: MDATA

Bits 14:4 BCNT : Byte count

Indicates the byte count of the received IN data packet.

Bits 3:0 CHNUM : Channel number

Indicates the channel number to which the current received packet belongs.

Device mode

Bits 31:25 Reserved, must be kept at reset value.

Bits 24:21 FRMNUM : Frame number

This is the least significant 4 bits of the frame number in which the packet is received on the USB. This field is supported only when isochronous OUT endpoints are supported.

Bits 20:17 PKTSTS : Packet status

Indicates the status of the received packet

0001: Global OUT NAK (triggers an interrupt)

0010: OUT data packet received

0011: OUT transfer completed (triggers an interrupt)

0100: SETUP transaction completed (triggers an interrupt)

0110: SETUP data packet received

Others: Reserved

Bits 16:15 DPID : Data PID

Indicates the Data PID of the received OUT data packet

00: DATA0

10: DATA1

01: DATA2

11: MDATA

Bits 14:4 BCNT : Byte count

Indicates the byte count of the received data packet.

Bits 3:0 EPNUM : Endpoint number

Indicates the endpoint number to which the current received packet belongs.

OTG_FS Receive FIFO size register (OTG_FS_GRXFSIZ)

Address offset: 0x024

Reset value: 0x0000 0200

The application can program the RAM size that must be allocated to the RxFIFO.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 RXFD : RxFIFO depth

This value is in terms of 32-bit words.

Minimum value is 16

Maximum value is 256

The power-on reset value of this register is specified as the largest Rx data FIFO depth.

OTG_FS Host non-periodic transmit FIFO size register
(OTG_FS_HNPTXFSIZ)/Endpoint 0 Transmit FIFO size (OTG_FS_DIEPTXF0)

Address offset: 0x028

Reset value: 0x0000 0200

Host mode

Bits 31:16 NPTXFD : Non-periodic TxFIFO depth

This value is in terms of 32-bit words.

Minimum value is 16

Maximum value is 256

Bits 15:0 NPTXFSA : Non-periodic transmit RAM start address

This field contains the memory start address for non-periodic transmit FIFO RAM.

Device mode

Bits 31:16 TX0FD : Endpoint 0 TxFIFO depth

This value is in terms of 32-bit words.

Minimum value is 16

Maximum value is 256

Bits 15:0 TX0FSA : Endpoint 0 transmit RAM start address

This field contains the memory start address for the endpoint 0 transmit FIFO RAM.

OTG_FS non-periodic transmit FIFO/queue status register
(OTG_FS_HNPTXSTS)

Address offset: 0x02C

Reset value: 0x0008 0200

Note: In Device mode, this register is not valid.

This read-only register contains the free space information for the non-periodic TxFIFO and the non-periodic transmit request queue.

Bit 31 Reserved, must be kept at reset value.

Bits 30:24 NPTXQTOP : Top of the non-periodic transmit request queue

Entry in the non-periodic Tx request queue that is currently being processed by the MAC.

Bits 30:27: Channel/endpoint number

Bits 26:25:

• – 00: IN/OUT token
• – 01: Zero-length transmit packet (device IN/host OUT)
• – 11: Channel halt command

Bit 24: Terminate (last entry for selected channel/endpoint)

Bits 23:16 NPTQXSAV : Non-periodic transmit request queue space available

Indicates the amount of free space available in the non-periodic transmit request queue. This queue holds both IN and OUT requests in host mode. Device mode has only IN requests.

00: Non-periodic transmit request queue is full

01: 1 location available

10: 2 locations available

bxn: n locations available ( \( 0 \leq n \leq 8 \) )

Others: Reserved

Bits 15:0 NPTXFSAV : Non-periodic TxFIFO space available

Indicates the amount of free space available in the non-periodic TxFIFO.

Values are in terms of 32-bit words.

00: Non-periodic TxFIFO is full

01: 1 word available

10: 2 words available

0xn: n words available (where \( 0 \leq n \leq 256 \) )

Others: Reserved

OTG_FS general core configuration register (OTG_FS_GCCFG)

Address offset: 0x038

Reset value: 0x0000 XXXX

Bits 31:22 Reserved, must be kept at reset value.

Bit 21 NOVBUSSENS : \( V_{BUS} \) sensing disable option

When this bit is set, \( V_{BUS} \) is considered internally to be always at \( V_{BUS} \) valid level (5 V). This option removes the need for a dedicated \( V_{BUS} \) pad, and leave this pad free to be used for other purposes such as a shared functionality. \( V_{BUS} \) connection can be remapped on another general purpose input pad and monitored by software.

This option is only suitable for host-only or device-only applications.

0: \( V_{BUS} \) sensing available by hardware

1: \( V_{BUS} \) sensing not available by hardware.

Bit 20 SOFOUTEN : SOF output enable

0: SOF pulse not available on PAD (OTG_FS_SOF)

1: SOF pulse available on PAD (OTG_FS_SOF)

Bit 19 VBUSBSEN : Enable the \( V_{BUS} \) sensing “B” device

0: \( V_{BUS} \) sensing “B” disabled

1: \( V_{BUS} \) sensing “B” enabled

Bit 18 VBUSASEN : Enable the \( V_{BUS} \) sensing “A” device

0: \( V_{BUS} \) sensing “A” disabled

1: \( V_{BUS} \) sensing “A” enabled

Bit 17 Reserved, must be kept at reset value.

Bit 16 PWRDWN : Power down

Used to activate the transceiver in transmission/reception

0: Power down active

1: Power down deactivated (“Transceiver active”)

Bits 15:0 Reserved, must be kept at reset value.

OTG_FS core ID register (OTG_FS_CID)

Address offset: 0x03C

Reset value: 0x0000 1200

This is a register containing the Product ID as reset value.

Bits 31:0 PRODUCT_ID : Product ID field

Application-programmable ID field.

OTG_FS Host periodic transmit FIFO size register (OTG_FS_HPTXFSIZ)

Address offset: 0x100

Reset value: 0x0200 0400

Bits 31:16 PTXFD : Host periodic TxFIFO depth

This value is in terms of 32-bit words.

Minimum value is 16

Bits 15:0 PTXSA : Host periodic TxFIFO start address

The power-on reset value of this register is the sum of the largest Rx data FIFO depth and largest non-periodic Tx data FIFO depth.

OTG_FS device IN endpoint transmit FIFO size register (OTG_FS_DIEPTXFx) (x = 1..3, where x is the FIFO_number)

Address offset: 0x104 + 0x04 * (x -1)

Reset value: 0x0200 0200

Bits 31:16 INEPTXFD : IN endpoint TxFIFO depth

This value is in terms of 32-bit words.

Minimum value is 16

The power-on reset value of this register is specified as the largest IN endpoint FIFO number depth.

Bits 15:0 INEPTXSA : IN endpoint FIFOx transmit RAM start address

This field contains the memory start address for IN endpoint transmit FIFOx. The address must be aligned with a 32-bit memory location.

22.16.3 Host-mode registers

Bit values in the register descriptions are expressed in binary unless otherwise specified.

Host-mode registers affect the operation of the core in the host mode. Host mode registers must not be accessed in device mode, as the results are undefined. Host mode registers can be categorized as follows:

OTG_FS Host configuration register (OTG_FS_HCFG)

Address offset: 0x400

Reset value: 0x0000 0000

This register configures the core after power-on. Do not make changes to this register after initializing the host.

Bits 31:3 Reserved, must be kept at reset value.

Bit 2 FSLSS : FS- and LS-only support

The application uses this bit to control the core's enumeration speed. Using this bit, the application can make the core enumerate as an FS host, even if the connected device supports HS traffic. Do not make changes to this field after initial programming.
1: FS/LS-only, even if the connected device can support HS (read-only)

Bits 1:0 FSLSPCS : FS/LS PHY clock select

When the core is in FS host mode

01: PHY clock is running at 48 MHz
Others: Reserved

When the core is in LS host mode

00: Reserved
01: Select 48 MHz PHY clock frequency
10: Select 6 MHz PHY clock frequency
11: Reserved

Note: The FSLSPCS must be set on a connection event according to the speed of the connected device (after changing this bit, a software reset must be performed).

OTG_FS Host frame interval register (OTG_FS_HFIR)

Address offset: 0x404

Reset value: 0x0000 EA60

This register stores the frame interval information for the current speed to which the OTG_FS controller has enumerated.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 FRIVL : Frame interval

The value that the application programs to this field specifies the interval between two consecutive SOFs (FS) or Keep-Alive tokens (LS). This field contains the number of PHY clocks that constitute the required frame interval. The application can write a value to this register only after the Port enable bit of the host port control and status register (PENA bit in OTG_FS_HPRT) has been set. If no value is programmed, the core calculates the value based on the PHY clock specified in the FS/LS PHY Clock Select field of the host configuration register (FSLSPCS in OTG_FS_HCFG). Do not change the value of this field after the initial configuration.

– Frame interval = 1 ms × (FRIVL - 1)

OTG_FS Host frame number/frame time remaining register (OTG_FS_HFNUM)

Address offset: 0x408

Reset value: 0x0000 3FFF

This register indicates the current frame number. It also indicates the time remaining (in terms of the number of PHY clocks) in the current frame.

Bits 31:16 FTREM : Frame time remaining

Indicates the amount of time remaining in the current frame, in terms of PHY clocks. This field decrements on each PHY clock. When it reaches zero, this field is reloaded with the value in the Frame interval register and a new SOF is transmitted on the USB.

Bits 15:0 FRNUM : Frame number

This field increments when a new SOF is transmitted on the USB, and is cleared to 0 when it reaches 0x3FFF.

OTG_FS Host periodic transmit FIFO/queue status register (OTG_FS_HPTXSTS)

Address offset: 0x410

Reset value: 0x0008 0100

This read-only register contains the free space information for the periodic TxFIFO and the periodic transmit request queue.

Bits 31:24 PTXQTOP : Top of the periodic transmit request queue

This indicates the entry in the periodic Tx request queue that is currently being processed by the MAC.

This register is used for debugging.

Bit 31: Odd/Even frame

• – 0: send in even frame
• – 1: send in odd frame

Bits 30:27: Channel/endpoint number

Bits 26:25: Type

• – 00: IN/OUT
• – 01: Zero-length packet
• – 11: Disable channel command

Bit 24: Terminate (last entry for the selected channel/endpoint)

Bits 23:16 PTXQSAV : Periodic transmit request queue space available

Indicates the number of free locations available to be written in the periodic transmit request queue. This queue holds both IN and OUT requests.

00: Periodic transmit request queue is full

01: 1 location available

10: 2 locations available

bxn: n locations available ( \( 0 \leq n \leq 8 \) )

Others: Reserved

Bits 15:0 PTXFSAVL : Periodic transmit data FIFO space available

Indicates the number of free locations available to be written to in the periodic TxFIFO.

Values are in terms of 32-bit words

0000: Periodic TxFIFO is full

0001: 1 word available

0010: 2 words available

bxn: n words available (where \( 0 \leq n \leq \text{PTXFD} \) )

Others: Reserved

OTG_FS Host all channels interrupt register (OTG_FS_HAINT)

Address offset: 0x414

Reset value: 0x0000 0000

When a significant event occurs on a channel, the host all channels interrupt register interrupts the application using the host channels interrupt bit of the Core interrupt register (HCINT bit in OTG_FS_GINTSTS). This is shown in Figure 250 . There is one interrupt bit per channel, up to a maximum of 16 bits. Bits in this register are set and cleared when the application sets and clears bits in the corresponding host channel-x interrupt register.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 HAINT : Channel interrupts

One bit per channel: Bit 0 for Channel 0, bit 15 for Channel 15

OTG_FS Host all channels interrupt mask register (OTG_FS_HAINTMSK)

Address offset: 0x418

Reset value: 0x0000 0000

The host all channel interrupt mask register works with the host all channel interrupt register to interrupt the application when an event occurs on a channel. There is one interrupt mask bit per channel, up to a maximum of 16 bits.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 HAINTM : Channel interrupt mask

0: Masked interrupt
1: Unmasked interrupt
One bit per channel: Bit 0 for channel 0, bit 15 for channel 15

OTG_FS Host port control and status register (OTG_FS_HPRT)

Address offset: 0x440

Reset value: 0x0000 0000

This register is available only in host mode. Currently, the OTG host supports only one port.

A single register holds USB port-related information such as USB reset, enable, suspend, resume, connect status, and test mode for each port. It is shown in Figure 250 . The rc_w1 bits in this register can trigger an interrupt to the application through the host port interrupt bit of the core interrupt register (HPRTINT bit in OTG_FS_GINTSTS). On a Port Interrupt, the application must read this register and clear the bit that caused the interrupt. For the rc_w1 bits, the application must write a 1 to the bit to clear the interrupt.

Bits 31:19 Reserved, must be kept at reset value.

Bits 18:17 PSPD : Port speed

Indicates the speed of the device attached to this port.

01: Full speed

10: Low speed

11: Reserved

The application writes a nonzero value to this field to put the port into a Test mode, and the corresponding pattern is signaled on the port.

0000: Test mode disabled

0001: Test_J mode

0010: Test_K mode

0011: Test_SE0_NAK mode

0100: Test_Packet mode

0101: Test_Force_Enable

Others: Reserved

The application uses this field to control power to this port, and the core clears this bit on an overcurrent condition.

0: Power off

1: Power on

Indicates the current logic level USB data lines

Bit 10: Logic level of OTG_FS_DP

Bit 11: Logic level of OTG_FS_DM

Bit 9 Reserved, must be kept at reset value.

When the application sets this bit, a reset sequence is started on this port. The application must time the reset period and clear this bit after the reset sequence is complete.

0: Port not in reset

1: Port in reset

The application must leave this bit set for a minimum duration of at least 10 ms to start a reset on the port. The application can leave it set for another 10 ms in addition to the required minimum duration, before clearing the bit, even though there is no maximum limit set by the USB standard.

The application sets this bit to put this port in Suspend mode. The core only stops sending SOFs when this is set. To stop the PHY clock, the application must set the Port clock stop bit, which asserts the suspend input pin of the PHY.

The read value of this bit reflects the current suspend status of the port. This bit is cleared by the core after a remote wake-up signal is detected or the application sets the Port reset bit or Port resume bit in this register or the Resume/remote wake-up detected interrupt bit or Disconnect detected interrupt bit in the Core interrupt register (WKUINT or DISCINT in OTG_FS_GINTSTS, respectively).

0: Port not in Suspend mode

1: Port in Suspend mode

The application sets this bit to drive resume signaling on the port. The core continues to drive the resume signal until the application clears this bit.

If the core detects a USB remote wake-up sequence, as indicated by the Port resume/remote wake-up detected interrupt bit of the Core interrupt register (WKUINT bit in OTG_FS_GINTSTS), the core starts driving resume signaling without application intervention and clears this bit when it detects a disconnect condition. The read value of this bit indicates whether the core is currently driving resume signaling.

0: No resume driven

1: Resume driven

Bit 5 POCCHNG : Port overcurrent change

The core sets this bit when the status of the Port overcurrent active bit (bit 4) in this register changes.

Bit 4 POCA : Port overcurrent active

Indicates the overcurrent condition of the port.

0: No overcurrent condition

1: Overcurrent condition

Bit 3 PENCHNG : Port enable/disable change

The core sets this bit when the status of the Port enable bit 2 in this register changes.

Bit 2 PENA : Port enable

A port is enabled only by the core after a reset sequence, and is disabled by an overcurrent condition, a disconnect condition, or by the application clearing this bit. The application cannot set this bit by a register write. It can only clear it to disable the port. This bit does not trigger any interrupt to the application.

0: Port disabled

1: Port enabled

Bit 1 PCDET : Port connect detected

The core sets this bit when a device connection is detected to trigger an interrupt to the application using the host port interrupt bit in the Core interrupt register (HPRTINT bit in OTG_FS_GINTSTS). The application must write a 1 to this bit to clear the interrupt.

Bit 0 PCSTS : Port connect status

0: No device is attached to the port

1: A device is attached to the port

OTG_FS Host channel-x characteristics register (OTG_FS_HCCHARx)
(x = 0..7, where x = Channel_number)

Address offset: 0x500 + 0x20 * x

Reset value: 0x0000 0000

Bit 31 CHENA : Channel enable

This field is set by the application and cleared by the OTG host.

0: Channel disabled

1: Channel enabled

Bit 30 CHDIS : Channel disable

The application sets this bit to stop transmitting/receiving data on a channel, even before the transfer for that channel is complete. The application must wait for the Channel disabled interrupt before treating the channel as disabled.

Bit 29 ODDFRM : Odd frame

This field is set (reset) by the application to indicate that the OTG host must perform a transfer in an odd frame. This field is applicable for only periodic (isochronous and interrupt) transactions.

0: Even frame

1: Odd frame

Bits 28:22 DAD : Device address

This field selects the specific device serving as the data source or sink.

Bits 21:20 MCNT : Multicount

This field indicates to the host the number of transactions that must be executed per frame for this periodic endpoint. For non-periodic transfers, this field is not used

00: Reserved. This field yields undefined results

01: 1 transaction

10: 2 transactions per frame to be issued for this endpoint

11: 3 transactions per frame to be issued for this endpoint

Note: This field must be set to at least 01.

Bits 19:18 EPTYP : Endpoint type

Indicates the transfer type selected.

00: Control

01: Isochronous

10: Bulk

11: Interrupt

Bit 17 LSDEV : Low-speed device

This field is set by the application to indicate that this channel is communicating to a low-speed device.

Bit 16 Reserved, must be kept at reset value.

Bit 15 EPDIR : Endpoint direction

Indicates whether the transaction is IN or OUT.

0: OUT

1: IN

Bits 14:11 EPNUM : Endpoint number

Indicates the endpoint number on the device serving as the data source or sink.

Bits 10:0 MPSIZ : Maximum packet size

Indicates the maximum packet size of the associated endpoint.

OTG_FS Host channel-x interrupt register (OTG_FS_HCINTx) (x = 0..7, where x = Channel_number)

Address offset: 0x508 + 0x20 * x

Reset value: 0x0000 0000

This register indicates the status of a channel with respect to USB- and AHB-related events. It is shown in Figure 250 . The application must read this register when the host channels interrupt bit in the Core interrupt register (HCINT bit in OTG_FS_GINTSTS) is set. Before the application can read this register, it must first read the host all channels interrupt (OTG_FS_HAINT) register to get the exact channel number for the host channel-x interrupt register. The application must clear the appropriate bit in this register to clear the corresponding bits in the OTG_FS_HAINT and OTG_FS_GINTSTS registers.

Bits 31:11 Reserved, must be kept at reset value.

Bit 10 DTERR : Data toggle error

Bit 9 FRMOR : Frame overrun

Bit 8 BBERR : Babble error

Bit 7 TXERR : Transaction error

Indicates one of the following errors occurred on the USB.

CRC check failure

Timeout

Bit stuff error

False EOP

Bit 6 Reserved, must be kept at reset value.

Bit 5 ACK : ACK response received/transmitted interrupt

Bit 4 NAK : NAK response received interrupt

Bit 3 STALL : STALL response received interrupt

Bit 2 Reserved, must be kept at reset value.

Bit 1 CHH : Channel halted

Indicates the transfer completed abnormally either because of any USB transaction error or in response to disable request by the application.

Bit 0 XFRC : Transfer completed

Transfer completed normally without any errors.

OTG_FS Host channel-x interrupt mask register (OTG_FS_HCINTMSKx)
(x = 0..7, where x = Channel_number)

Address offset: 0x50C + 0x20 * x

Reset value: 0x0000 0000

This register reflects the mask for each channel status described in the previous section.

Bits 31:11 Reserved, must be kept at reset value.

Bit 10 DTERRM : Data toggle error mask

0: Masked interrupt

1: Unmasked interrupt

Bit 9 FRMORM : Frame overrun mask

0: Masked interrupt

1: Unmasked interrupt

Bit 8 BBERRM : Babble error mask

0: Masked interrupt

1: Unmasked interrupt

Bit 7 TXERRM : Transaction error mask

0: Masked interrupt

1: Unmasked interrupt

Bit 6 Reserved, must be kept at reset value.

Bit 5 ACKM : ACK response received/transmitted interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Bit 4 NAKM : NAK response received interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Bit 3 STALLM : STALL response received interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Bit 2 Reserved, must be kept at reset value.

Bit 1 CHHM : Channel halted mask

• 0: Masked interrupt
• 1: Unmasked interrupt

Bit 0 XFRCM : Transfer completed mask

• 0: Masked interrupt
• 1: Unmasked interrupt

OTG_FS Host channel-x transfer size register (OTG_FS_HCTSIZx) (x = 0..7, where x = Channel_number)

Address offset: 0x510 + 0x20 * x

Reset value: 0x0000 0000

Bit 31 Reserved, must be kept at reset value.

Bits 30:29 DPID : Data PID

The application programs this field with the type of PID to use for the initial transaction. The host maintains this field for the rest of the transfer.

• 00: DATA0
• 01: DATA2
• 10: DATA1
• 11: MDATA (non-control)/SETUP (control)

Bits 28:19 PKTCNT : Packet count

This field is programmed by the application with the expected number of packets to be transmitted (OUT) or received (IN).

The host decrements this count on every successful transmission or reception of an OUT/IN packet. Once this count reaches zero, the application is interrupted to indicate normal completion.

Bits 18:0 XFRSIZ : Transfer size

For an OUT, this field is the number of data bytes the host sends during the transfer.

For an IN, this field is the buffer size that the application has reserved for the transfer. The application is expected to program this field as an integer multiple of the maximum packet size for IN transactions (periodic and non-periodic).

22.16.4 Device-mode registers

OTG_FS device configuration register (OTG_FS_DCFG)

Address offset: 0x800

Reset value: 0x0220 0000

This register configures the core in device mode after power-on or after certain control commands or enumeration. Do not make changes to this register after initial programming.

Bits 31:13 Reserved, must be kept at reset value.

Bits 12:11 PFIVL : Periodic frame interval

Indicates the time within a frame at which the application must be notified using the end of periodic frame interrupt. This can be used to determine if all the isochronous traffic for that frame is complete.

00: 80% of the frame interval

01: 85% of the frame interval

10: 90% of the frame interval

11: 95% of the frame interval

Bits 10:4 DAD : Device address

The application must program this field after every SetAddress control command.

Bit 3 Reserved, must be kept at reset value.

Bit 2 NZLSOHSK : Non-zero-length status OUT handshake

The application can use this field to select the handshake the core sends on receiving a nonzero-length data packet during the OUT transaction of a control transfer's Status stage.

1: Send a STALL handshake on a nonzero-length status OUT transaction and do not send the received OUT packet to the application.

0: Send the received OUT packet to the application (zero-length or nonzero-length) and send a handshake based on the NAK and STALL bits for the endpoint in the Device endpoint control register.

Bits 1:0 DSPD : Device speed

Indicates the speed at which the application requires the core to enumerate, or the maximum speed the application can support. However, the actual bus speed is determined only after the chirp sequence is completed, and is based on the speed of the USB host to which the core is connected.

00: Reserved

01: Reserved

10: Reserved

11: Full speed (USB 1.1 transceiver clock is 48 MHz)

OTG_FS device control register (OTG_FS_DCTL)

Address offset: 0x804

Reset value: 0x0000 0000

Bits 31:12 Reserved, must be kept at reset value.

Bit 11 POPRGDNE : Power-on programming done

The application uses this bit to indicate that register programming is completed after a wake-up from power down mode.

Bit 10 CGONAK : Clear global OUT NAK

Writing 1 to this field clears the Global OUT NAK.

Bit 9 SGONAK : Set global OUT NAK

Writing 1 to this field sets the Global OUT NAK.

The application uses this bit to send a NAK handshake on all OUT endpoints.

The application must set the this bit only after making sure that the Global OUT NAK effective bit in the Core interrupt register (GONAKEFF bit in OTG_FS_GINTSTS) is cleared.

Bit 8 CGINAK : Clear global IN NAK

Writing 1 to this field clears the Global IN NAK.

Bit 7 SGINAK : Set global IN NAK

Writing 1 to this field sets the Global non-periodic IN NAK. The application uses this bit to send a NAK handshake on all non-periodic IN endpoints.

The application must set this bit only after making sure that the Global IN NAK effective bit in the Core interrupt register (GINAKEFF bit in OTG_FS_GINTSTS) is cleared.

Bits 6:4 TCTL : Test control

000: Test mode disabled

001: Test_J mode

010: Test_K mode

011: Test_SE0_NAK mode

100: Test_Packet mode

101: Test_Force_Enable

Others: Reserved

Bit 3 GONSTS : Global OUT NAK status

0: A handshake is sent based on the FIFO Status and the NAK and STALL bit settings.

1: No data is written to the RxFIFO, irrespective of space availability. Sends a NAK handshake on all packets, except on SETUP transactions. All isochronous OUT packets are dropped.

Bit 2 GINSTS : Global IN NAK status

0: A handshake is sent out based on the data availability in the transmit FIFO.

1: A NAK handshake is sent out on all non-periodic IN endpoints, irrespective of the data availability in the transmit FIFO.

Bit 1 SDIS : Soft disconnect

The application uses this bit to signal the USB OTG core to perform a soft disconnect. As long as this bit is set, the host does not see that the device is connected, and the device does not receive signals on the USB. The core stays in the disconnected state until the application clears this bit.

0: Normal operation. When this bit is cleared after a soft disconnect, the core generates a device connect event to the USB host. When the device is reconnected, the USB host restarts device enumeration.

1: The core generates a device disconnect event to the USB host.

Bit 0 RWUSIG : Remote wake-up signaling

When the application sets this bit, the core initiates remote signaling to wake up the USB host. The application must set this bit to instruct the core to exit the Suspend state. As specified in the USB 2.0 specification, the application must clear this bit 1 ms to 15 ms after setting it.

Table 134 contains the minimum duration (according to device state) for which the Soft disconnect (SDIS) bit must be set for the USB host to detect a device disconnect. To accommodate clock jitter, it is recommended that the application add some extra delay to the specified minimum duration.

Table 134. Minimum duration for soft disconnect

OTG_FS device status register (OTG_FS_DSTS)

Address offset: 0x808

Reset value: 0x0000 0010

This register indicates the status of the core with respect to USB-related events. It must be read on interrupts from the device all interrupts (OTG_FS_DAINT) register.

Bits 31:22 Reserved, must be kept at reset value.

Bits 21:8 FNSOF : Frame number of the received SOF

Bits 7:4 Reserved, must be kept at reset value.

Bit 3 EERR : Erratic error

The core sets this bit to report any erratic errors.

Due to erratic errors, the OTG_FS controller goes into Suspended state and an interrupt is generated to the application with Early suspend bit of the OTG_FS_GINTSTS register (ESUSP bit in OTG_FS_GINTSTS). If the early suspend is asserted due to an erratic error, the application can only perform a soft disconnect/recover.

Bits 2:1 ENUMSPD : Enumerated speed

Indicates the speed at which the OTG_FS controller has come up after speed detection through a chirp sequence.

01: Reserved

10: Reserved

11: Full speed (PHY clock is running at 48 MHz)

Others: reserved

Bit 0 SUSPSTS : Suspend status

In device mode, this bit is set as long as a Suspend condition is detected on the USB. The core enters the Suspended state when there is no activity on the USB data lines for a period of 3 ms. The core comes out of the suspend:

• – When there is an activity on the USB data lines
• – When the application writes to the Remote wake-up signaling bit in the OTG_FS_DCTL register (RWUSIG bit in OTG_FS_DCTL).

OTG_FS device IN endpoint common interrupt mask register (OTG_FS_DIEPMSK)

Address offset: 0x810

Reset value: 0x0000 0000

This register works with each of the OTG_FS_DIEPINTx registers for all endpoints to generate an interrupt per IN endpoint. The IN endpoint interrupt for a specific status in the OTG_FS_DIEPINTx register can be masked by writing to the corresponding bit in this register. Status bits are masked by default.

Bits 31:14 Reserved, must be kept at reset value.

Bit 13 NAKM : NAK interrupt mask

0: Masked interrupt

1: Unmasked interrupt

Bits 12:7 Reserved, must be kept at reset value.

Bit 6 INEPNE : IN endpoint NAK effective mask

0: Masked interrupt

1: Unmasked interrupt

1. Bit 5 INEPNMM : IN token received with EP mismatch mask
   0: Masked interrupt
   1: Unmasked interrupt
2. Bit 4 ITTXFEMSK : IN token received when TxFIFO empty mask
   0: Masked interrupt
   1: Unmasked interrupt
3. Bit 3 TOM : Timeout condition mask (Non-isochronous endpoints)
   0: Masked interrupt
   1: Unmasked interrupt
4. Bit 2 Reserved, must be kept at reset value.
5. Bit 1 EPDM : Endpoint disabled interrupt mask
   0: Masked interrupt
   1: Unmasked interrupt
6. Bit 0 XFRCM : Transfer completed interrupt mask
   0: Masked interrupt
   1: Unmasked interrupt

OTG_FS device OUT endpoint common interrupt mask register (OTG_FS_DOEPMSK)

Address offset: 0x814

Reset value: 0x0000 0000

This register works with each of the OTG_FS_DOEPINTx registers for all endpoints to generate an interrupt per OUT endpoint. The OUT endpoint interrupt for a specific status in the OTG_FS_DOEPINTx register can be masked by writing into the corresponding bit in this register. Status bits are masked by default.

Bits 31:14 Reserved, must be kept at reset value.

Bit 13 NAKMSK : NAK interrupt mask

1. 0: Masked interrupt
   1: Unmasked interrupt

Bit 12 BERRM : Babble error interrupt mask

1. 0: Masked interrupt
   1: Unmasked interrupt

Bits 11:9 Reserved, must be kept at reset value.

Bit 8 OUTPKTERRM : Out packet error mask

1. 0: Masked interrupt
   1: Unmasked interrupt

Bits 7:6 Reserved, must be kept at reset value.

Bit 5 STSPHSRXM : Status phase received for control write mask

• 0: Masked interrupt
• 1: Unmasked interrupt

Bit 4 OTEPDM : OUT token received when endpoint disabled mask

• Applies to control OUT endpoints only.
• 0: Masked interrupt
• 1: Unmasked interrupt

Bit 3 STUPM : SETUP phase done mask

• Applies to control endpoints only.
• 0: Masked interrupt
• 1: Unmasked interrupt

Bit 2 Reserved, must be kept at reset value.

Bit 1 EPDM : Endpoint disabled interrupt mask

• 0: Masked interrupt
• 1: Unmasked interrupt

Bit 0 XFRCM : Transfer completed interrupt mask

• 0: Masked interrupt
• 1: Unmasked interrupt

OTG_FS device all endpoints interrupt register (OTG_FS_DAINT)

Address offset: 0x818

Reset value: 0x0000 0000

When a significant event occurs on an endpoint, a OTG_FS_DAINT register interrupts the application using the Device OUT endpoints interrupt bit or Device IN endpoints interrupt bit of the OTG_FS_GINTSTS register (OEPINT or IEPINT in OTG_FS_GINTSTS, respectively). There is one interrupt bit per endpoint, up to a maximum of 16 bits for OUT endpoints and 16 bits for IN endpoints. For a bidirectional endpoint, the corresponding IN and OUT interrupt bits are used. Bits in this register are set and cleared when the application sets and clears bits in the corresponding Device Endpoint-x interrupt register (OTG_FS_DIEPINTx/OTG_FS_DOEPINTx).

Bits 31:16 OEPINT : OUT endpoint interrupt bits

• One bit per OUT endpoint:
• Bit 16 for OUT endpoint 0, bit 19 for OUT endpoint 3.

Bits 15:0 IEPINT : IN endpoint interrupt bits

• One bit per IN endpoint:
• Bit 0 for IN endpoint 0, bit 3 for endpoint 3.

OTG_FS all endpoints interrupt mask register (OTG_FS_DAINMSK)

Address offset: 0x81C

Reset value: 0x0000 0000

The OTG_FS_DAINMSK register works with the Device endpoint interrupt register to interrupt the application when an event occurs on a device endpoint. However, the OTG_FS_DAIN register bit corresponding to that interrupt is still set.

Bits 31:16 OEPM : OUT EP interrupt mask bits

One per OUT endpoint:
Bit 16 for OUT EP 0, bit 19 for OUT EP 3
0: Masked interrupt
1: Unmasked interrupt

Bits 15:0 IEPM : IN EP interrupt mask bits

One bit per IN endpoint:
Bit 0 for IN EP 0, bit 3 for IN EP 3
0: Masked interrupt
1: Unmasked interrupt

OTG_FS device V _BUS discharge time register (OTG_FS_DVBUSDIS)

Address offset: 0x0828

Reset value: 0x0000 17D7

This register specifies the V _BUS discharge time after V _BUS pulsing during SRP.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 VBUSDT : Device V _BUS discharge time

Specifies the V _BUS discharge time after V _BUS pulsing during SRP. This value equals:
V _BUS discharge time in PHY clocks / 1 024
Depending on your V _BUS load, this value may need adjusting.

OTG_FS device V _BUS pulsing time register (OTG_FS_DVBUSPULSE)

Address offset: 0x082C

Reset value: 0x0000 05B8

This register specifies the V _BUS pulsing time during SRP.

Bits 31:12 Reserved, must be kept at reset value.

Bits 11:0 DVBUSP : Device V _BUS pulsing time

Specifies the V _BUS pulsing time during SRP. This value equals:

V _BUS pulsing time in PHY clocks / 1 024

OTG_FS device IN endpoint FIFO empty interrupt mask register: (OTG_FS_DIEPMPMSK)

Address offset: 0x834

Reset value: 0x0000 0000

This register is used to control the IN endpoint FIFO empty interrupt generation (TXFE_OTG_FS_DIEPINTx).

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:0 INEPTXFEM : IN EP Tx FIFO empty interrupt mask bits

These bits act as mask bits for OTG_FS_DIEPINTx.

TXFE interrupt one bit per IN endpoint:

Bit 0 for IN endpoint 0, bit 3 for IN endpoint 3

0: Masked interrupt

1: Unmasked interrupt

OTG_FS device control IN endpoint 0 control register (OTG_FS_DIEPCTL0)

Address offset: 0x900

Reset value: 0x0000 0000

This section describes the OTG_FS_DIEPCTL0 register. Nonzero control endpoints use registers for endpoints 1–3.

Bit 31 EPENA : Endpoint enable

The application sets this bit to start transmitting data on the endpoint 0.

The core clears this bit before setting any of the following interrupts on this endpoint:

• – Endpoint disabled
• – Transfer completed

Bit 30 EPDIS : Endpoint disable

The application sets this bit to stop transmitting data on an endpoint, even before the transfer for that endpoint is complete. The application must wait for the Endpoint disabled interrupt before treating the endpoint as disabled. The core clears this bit before setting the Endpoint disabled interrupt. The application must set this bit only if Endpoint enable is already set for this endpoint.

Bits 29:28 Reserved, must be kept at reset value.

Bit 27 SNAK : Set NAK

A write to this bit sets the NAK bit for the endpoint.

Using this bit, the application can control the transmission of NAK handshakes on an endpoint. The core can also set this bit for an endpoint after a SETUP packet is received on that endpoint.

Bit 26 CNAK : Clear NAK

A write to this bit clears the NAK bit for the endpoint.

Bits 25:22 TXFNUM : TxFIFO number

This value is set to the FIFO number that is assigned to IN endpoint 0.

Bit 21 STALL : STALL handshake

The application can only set this bit, and the core clears it when a SETUP token is received for this endpoint. If a NAK bit, a Global IN NAK or Global OUT NAK is set along with this bit, the STALL bit takes priority.

Bit 20 Reserved, must be kept at reset value.

Bits 19:18 EPTYP : Endpoint type

Hardcoded to '00' for control.

Bit 17 NAKSTS : NAK status

Indicates the following:

0: The core is transmitting non-NAK handshakes based on the FIFO status

1: The core is transmitting NAK handshakes on this endpoint.

When this bit is set, either by the application or core, the core stops transmitting data, even if there are data available in the TxFIFO. Irrespective of this bit's setting, the core always responds to SETUP data packets with an ACK handshake.

Bit 16 Reserved, must be kept at reset value.

Bit 15 USBAEP : USB active endpoint

This bit is always set to 1, indicating that control endpoint 0 is always active in all configurations and interfaces.

Bits 14:2 Reserved, must be kept at reset value.

Bits 1:0 MPSIZ : Maximum packet size

The application must program this field with the maximum packet size for the current logical endpoint.

00: 64 bytes

01: 32 bytes

10: 16 bytes

11: 8 bytes

OTG device endpoint x control register (OTG_FS_DIEPCTLx) (x = 1..3, where x = Endpoint_number)

Address offset: 0x900 + 0x20 * x

Reset value: 0x0000 0000

The application uses this register to control the behavior of each logical endpoint other than endpoint 0.

Bit 31 EPENA : Endpoint enable

The application sets this bit to start transmitting data on an endpoint.

The core clears this bit before setting any of the following interrupts on this endpoint:

• - SETUP phase done
• - Endpoint disabled
• - Transfer completed

Bit 30 EPDIS : Endpoint disable

The application sets this bit to stop transmitting/receiving data on an endpoint, even before the transfer for that endpoint is complete. The application must wait for the Endpoint disabled interrupt before treating the endpoint as disabled. The core clears this bit before setting the Endpoint disabled interrupt. The application must set this bit only if Endpoint enable is already set for this endpoint.

Bit 29 SODDFRM : Set odd frame

Applies to isochronous IN and OUT endpoints only.

Writing to this field sets the Even/Odd frame (EONUM) field to odd frame.

Applies to interrupt/bulk IN endpoints only.

Writing to this field sets the endpoint data PID (DPID) field in this register to DATA0.

Applies to isochronous IN endpoints only.

Writing to this field sets the Even/Odd frame (EONUM) field to even frame.

A write to this bit sets the NAK bit for the endpoint.

Using this bit, the application can control the transmission of NAK handshakes on an endpoint. The core can also set this bit for OUT endpoints on a Transfer completed interrupt, or after a SETUP is received on the endpoint.

A write to this bit clears the NAK bit for the endpoint.

These bits specify the FIFO number associated with this endpoint. Each active IN endpoint must be programmed to a separate FIFO number.

This field is valid only for IN endpoints.

Applies to non-control, non-isochronous IN endpoints only (access type is rw).

The application sets this bit to stall all tokens from the USB host to this endpoint. If a NAK bit, Global IN NAK, or Global OUT NAK is set along with this bit, the STALL bit takes priority. Only the application can clear this bit, never the core.

This is the transfer type supported by this logical endpoint.

00: Control

01: Isochronous

10: Bulk

11: Interrupt

It indicates the following:

0: The core is transmitting non-NAK handshakes based on the FIFO status.

1: The core is transmitting NAK handshakes on this endpoint.

When either the application or the core sets this bit:

For non-isochronous IN endpoints: The core stops transmitting any data on an IN endpoint, even if there are data available in the TxFIFO.

For isochronous IN endpoints: The core sends out a zero-length data packet, even if there are data available in the TxFIFO.

Irrespective of this bit's setting, the core always responds to SETUP data packets with an ACK handshake.

Bit 16 EONUM : Even/odd frame

Applies to isochronous IN endpoints only.

Indicates the frame number in which the core transmits/receives isochronous data for this endpoint. The application must program the even/odd frame number in which it intends to transmit/receive isochronous data for this endpoint using the SEVNFRM and SODDFRM fields in this register.

0: Even frame

1: Odd frame

DPID : Endpoint data PID

Applies to interrupt/bulk IN endpoints only.

Contains the PID of the packet to be received or transmitted on this endpoint. The application must program the PID of the first packet to be received or transmitted on this endpoint, after the endpoint is activated. The application uses the SD0PID register field to program either DATA0 or DATA1 PID.

0: DATA0

1: DATA1

Bit 15 USBAEP : USB active endpoint

Indicates whether this endpoint is active in the current configuration and interface. The core clears this bit for all endpoints (other than EP 0) after detecting a USB reset. After receiving the SetConfiguration and SetInterface commands, the application must program endpoint registers accordingly and set this bit.

Bits 14:11 Reserved, must be kept at reset value.

Bits 10:0 MPISZ : Maximum packet size

The application must program this field with the maximum packet size for the current logical endpoint. This value is in bytes.

OTG_FS device control OUT endpoint 0 control register
(OTG_FS_DOEPCTL0)

Address offset: 0xB00

Reset value: 0x0000 8000

This section describes the OTG_FS_DOEPCTL0 register. Nonzero control endpoints use registers for endpoints 1–3.

Bit 31 EPENA : Endpoint enable

The application sets this bit to start transmitting data on endpoint 0.

The core clears this bit before setting any of the following interrupts on this endpoint:

• – SETUP phase done
• – Endpoint disabled
• – Transfer completed

Bit 30 EPDIS : Endpoint disable

The application cannot disable control OUT endpoint 0.

Bits 29:28 Reserved, must be kept at reset value.

Bit 27 SNAK : Set NAK

A write to this bit sets the NAK bit for the endpoint.

Using this bit, the application can control the transmission of NAK handshakes on an endpoint. The core can also set this bit on a Transfer completed interrupt, or after a SETUP is received on the endpoint.

Bit 26 CNAK : Clear NAK

A write to this bit clears the NAK bit for the endpoint.

Bits 25:22 Reserved, must be kept at reset value.

Bit 21 STALL : STALL handshake

The application can only set this bit, and the core clears it, when a SETUP token is received for this endpoint. If a NAK bit or Global OUT NAK is set along with this bit, the STALL bit takes priority. Irrespective of this bit's setting, the core always responds to SETUP data packets with an ACK handshake.

Bit 20 SNPM : Snoop mode

This bit configures the endpoint to Snoop mode. In Snoop mode, the core does not check the correctness of OUT packets before transferring them to application memory.

Bits 19:18 EPTYP : Endpoint type

Hardcoded to 2'b00 for control.

Bit 17 NAKSTS : NAK status

Indicates the following:

0: The core is transmitting non-NAK handshakes based on the FIFO status.

1: The core is transmitting NAK handshakes on this endpoint.

When either the application or the core sets this bit, the core stops receiving data, even if there is space in the RxFIFO to accommodate the incoming packet. Irrespective of this bit's setting, the core always responds to SETUP data packets with an ACK handshake.

Bit 16 Reserved, must be kept at reset value.

Bit 15 USBAEP : USB active endpoint

This bit is always set to 1, indicating that a control endpoint 0 is always active in all configurations and interfaces.

Bits 14:2 Reserved, must be kept at reset value.

Bits 1:0 MPSIZ : Maximum packet size

The maximum packet size for control OUT endpoint 0 is the same as what is programmed in control IN endpoint 0.

00: 64 bytes

01: 32 bytes

10: 16 bytes

11: 8 bytes

OTG_FS device endpoint-x control register (OTG_FS_DOEPCTLx) (x = 1..3, where x = Endpoint_number)

Address offset for OUT endpoints: 0xB00 + 0x20 * x

Reset value: 0x0000 0000

The application uses this register to control the behavior of each logical endpoint other than endpoint 0.

Bit 31 EPENA : Endpoint enable

Applies to IN and OUT endpoints.

The application sets this bit to start transmitting data on an endpoint.

The core clears this bit before setting any of the following interrupts on this endpoint:

• - SETUP phase done
• - Endpoint disabled
• - Transfer completed

The application sets this bit to stop transmitting/receiving data on an endpoint, even before the transfer for that endpoint is complete. The application must wait for the Endpoint disabled interrupt before treating the endpoint as disabled. The core clears this bit before setting the Endpoint disabled interrupt. The application must set this bit only if Endpoint enable is already set for this endpoint.

Applies to interrupt/bulk IN and OUT endpoints only. Writing to this field sets the endpoint data PID (DPID) field in this register to DATA1.

Applies to isochronous IN and OUT endpoints only. Writing to this field sets the Even/Odd frame (EONUM) field to odd frame.

Applies to interrupt/bulk OUT endpoints only.

Writing to this field sets the endpoint data PID (DPID) field in this register to DATA0.

Applies to isochronous OUT endpoints only.

Writing to this field sets the Even/Odd frame (EONUM) field to even frame.

A write to this bit sets the NAK bit for the endpoint.

Using this bit, the application can control the transmission of NAK handshakes on an endpoint. The core can also set this bit for OUT endpoints on a Transfer Completed interrupt, or after a SETUP is received on the endpoint.

A write to this bit clears the NAK bit for the endpoint.

Bits 25:22 Reserved, must be kept at reset value.

Applies to non-control, non-isochronous OUT endpoints only (access type is rw).

The application sets this bit to stall all tokens from the USB host to this endpoint. If a NAK bit, Global IN NAK, or Global OUT NAK is set along with this bit, the STALL bit takes priority. Only the application can clear this bit, never the core.

This bit configures the endpoint to Snoop mode. In Snoop mode, the core does not check the correctness of OUT packets before transferring them to application memory.

This is the transfer type supported by this logical endpoint.

00: Control

01: Isochronous

10: Bulk

11: Interrupt

Indicates the following:

0: The core is transmitting non-NAK handshakes based on the FIFO status.

1: The core is transmitting NAK handshakes on this endpoint.

When either the application or the core sets this bit:

The core stops receiving any data on an OUT endpoint, even if there is space in the RxFIFO to accommodate the incoming packet.

Irrespective of this bit's setting, the core always responds to SETUP data packets with an ACK handshake.

Applies to isochronous IN and OUT endpoints only.

Indicates the frame number in which the core transmits/receives isochronous data for this endpoint. The application must program the even/odd frame number in which it intends to transmit/receive isochronous data for this endpoint using the SEVNFRM and SODDFRM fields in this register.

0: Even frame

1: Odd frame

Applies to interrupt/bulk OUT endpoints only.

Contains the PID of the packet to be received or transmitted on this endpoint. The application must program the PID of the first packet to be received or transmitted on this endpoint, after the endpoint is activated. The application uses the SD0PID register field to program either DATA0 or DATA1 PID.

0: DATA0

1: DATA1

Indicates whether this endpoint is active in the current configuration and interface. The core clears this bit for all endpoints (other than EP 0) after detecting a USB reset. After receiving the SetConfiguration and SetInterface commands, the application must program endpoint registers accordingly and set this bit.

Bits 14:11 Reserved, must be kept at reset value.

The application must program this field with the maximum packet size for the current logical endpoint. This value is in bytes.

OTG_FS device endpoint-x interrupt register (OTG_FS_DIEPINTx) (x = 0..3, where x = Endpoint_number)

Address offset: 0x908 + 0x20 * x

Reset value: 0x0000 0080

This register indicates the status of an endpoint with respect to USB- and AHB-related events. It is shown in Figure 250 . The application must read this register when the IN endpoints interrupt bit of the Core interrupt register (IEPINT in OTG_FS_GINTSTS) is set. Before the application can read this register, it must first read the device all endpoints interrupt (OTG_FS_DAINT) register to get the exact endpoint number for the Device endpoint-x interrupt register. The application must clear the appropriate bit in this register to clear the corresponding bits in the OTG_FS_DAINT and OTG_FS_GINTSTS registers.

Bits 31:14 Reserved, must be kept at reset value.

Bit 13 NAK : NAK input

The core generates this interrupt when a NAK is transmitted or received by the device. In case of isochronous IN endpoints the interrupt gets generated when a zero length packet is transmitted due to unavailability of data in the Tx FIFO.

Bit 12 Reserved, must be kept at reset value.

Bit 11 PKTDRPSTS : Packet dropped status

This bit indicates to the application that an ISOC OUT packet has been dropped. This bit does not have an associated mask bit and does not generate an interrupt.

Bits 10:8 Reserved, must be kept at reset value.

Bit 7 TXFE : Transmit FIFO empty

This interrupt is asserted when the TxFIFO for this endpoint is either half or completely empty. The half or completely empty status is determined by the TxFIFO Empty Level bit in the OTG_FS_GAHBCFG register (TXFELVL bit in OTG_FS_GAHBCFG).

Bit 6 INEPNE : IN endpoint NAK effective

This bit can be cleared when the application clears the IN endpoint NAK by writing to the CNAK bit in OTG_FS_DIEPCTLx.

This interrupt indicates that the core has sampled the NAK bit set (either by the application or by the core). The interrupt indicates that the IN endpoint NAK bit set by the application has taken effect in the core.

This interrupt does not guarantee that a NAK handshake is sent on the USB. A STALL bit takes priority over a NAK bit.

Bit 5 INEPNM : IN token received with EP mismatch.

Indicates that the data in the top of the non-periodic TxFIFO belongs to an endpoint other than the one for which the IN token was received. This interrupt is asserted on the endpoint for which the IN token was received.

Bit 4 ITTXFE : IN token received when TxFIFO is empty

Applies to non-periodic IN endpoints only.

Indicates that an IN token was received when the associated TxFIFO (periodic/non-periodic) was empty. This interrupt is asserted on the endpoint for which the IN token was received.

Bit 3 TOC : Timeout condition

Applies only to Control IN endpoints.

Indicates that the core has detected a timeout condition on the USB for the last IN token on this endpoint.

Bit 2 Reserved, must be kept at reset value.

Bit 1 EPDISD : Endpoint disabled interrupt

This bit indicates that the endpoint is disabled per the application's request.

Bit 0 XFRC : Transfer completed interrupt

This field indicates that the programmed transfer is complete on the AHB as well as on the USB, for this endpoint.

OTG_FS device endpoint-x interrupt register (OTG_FS_DOEPINTx) (x = 0..3, where x = Endpoint_number)

Address offset: 0xB08 + 0x20 * x

Reset value: 0x0000 0080

This register indicates the status of an endpoint with respect to USB- and AHB-related events. It is shown in Figure 250 . The application must read this register when the OUT Endpoints Interrupt bit of the OTG_FS_GINTSTS register (OEPINT bit in OTG_FS_GINTSTS) is set. Before the application can read this register, it must first read the OTG_FS_DAINTR register to get the exact endpoint number for the OTG_FS_DOEPINTx register. The application must clear the appropriate bit in this register to clear the corresponding bits in the OTG_FS_DAINTR and OTG_FS_GINTSTS registers.

Bits 31:14 Reserved, must be kept at reset value.

Bit 13 NAK : NAK input

The core generates this interrupt when a NAK is transmitted or received by the device. In case of isochronous IN endpoints the interrupt gets generated when a zero length packet is transmitted due to unavailability of data in the Tx FIFO.

Bit 12 BERR : Babble error interrupt

The core generates this interrupt when babble is received for the endpoint.

Bits 11:9 Reserved, must be kept at reset value.

Bit 8 OUTPKTERR : OUT packet error

This interrupt is asserted when the core detects an overflow or a CRC error for an OUT packet. This interrupt is valid only when thresholding is enabled.

Bits 7:6 Reserved, must be kept at reset value.

Bit 5 STSPHSRX : Status phase received for control write

This interrupt is generated only after the core has transferred all the data that the host has sent during the data phase of a control write transfer, to the system memory buffer. The interrupt indicates to the application that the host has switched from data phase to the status phase of a control write transfer. The application can use this interrupt to ACK or STALL the status phase, after it has decoded the data phase.

Bit 4 OTEPDIS : OUT token received when endpoint disabled

Applies only to control OUT endpoints.

Indicates that an OUT token was received when the endpoint was not yet enabled. This interrupt is asserted on the endpoint for which the OUT token was received.

Bit 3 STUP : SETUP phase done

Applies to control OUT endpoint only.

Indicates that the SETUP phase for the control endpoint is complete and no more back-to-back SETUP packets were received for the current control transfer. On this interrupt, the application can decode the received SETUP data packet.

Bit 2 Reserved, must be kept at reset value.

Bit 1 EPDISD : Endpoint disabled interrupt

This bit indicates that the endpoint is disabled per the application's request.

Bit 0 XFRC : Transfer completed interrupt

This field indicates that the programmed transfer is complete on the AHB as well as on the USB, for this endpoint.

OTG_FS device IN endpoint 0 transfer size register (OTG_FS_DIEPTSIZ0)

Address offset: 0x910

Reset value: 0x0000 0000

The application must modify this register before enabling endpoint 0. Once endpoint 0 is enabled using the endpoint enable bit in the device control endpoint 0 control registers (EPENA in OTG_FS_DIEPCTL0), the core modifies this register. The application can only read this register once the core has cleared the Endpoint enable bit.

Nonzero endpoints use the registers for endpoints 1–3.

Bits 31:21 Reserved, must be kept at reset value.

Bits 20:19 PKTCNT : Packet count

Indicates the total number of USB packets that constitute the Transfer Size amount of data for endpoint 0.

This field is decremented every time a packet (maximum size or short packet) is read from the TxFIFO.

Bits 18:7 Reserved, must be kept at reset value.

Bits 6:0 XFRSIZ : Transfer size

Indicates the transfer size in bytes for endpoint 0. The core interrupts the application only after it has exhausted the transfer size amount of data. The transfer size can be set to the maximum packet size of the endpoint, to be interrupted at the end of each packet.

The core decrements this field every time a packet from the external memory is written to the TxFIFO.

OTG_FS device OUT endpoint 0 transfer size register (OTG_FS_DOEPTSIZ0)

Address offset: 0xB10

Reset value: 0x0000 0000

The application must modify this register before enabling endpoint 0. Once endpoint 0 is enabled using the Endpoint enable bit in the OTG_FS_DOEPCTL0 registers (EPENA bit in OTG_FS_DOEPCTL0), the core modifies this register. The application can only read this register once the core has cleared the Endpoint enable bit.

Nonzero endpoints use the registers for endpoints 1–3.

Bit 31 Reserved, must be kept at reset value.

Bits 30:29 STUPCNT : SETUP packet count

This field specifies the number of back-to-back SETUP data packets the endpoint can receive.

01: 1 packet

10: 2 packets

11: 3 packets

Bits 28:20 Reserved, must be kept at reset value.

Bit 19 PKTCNT : Packet count

This field is decremented to zero after a packet is written into the RxFIFO.

Bits 18:7 Reserved, must be kept at reset value.

Bits 6:0 XFRSIZ : Transfer size

Indicates the transfer size in bytes for endpoint 0. The core interrupts the application only after it has exhausted the transfer size amount of data. The transfer size can be set to the maximum packet size of the endpoint, to be interrupted at the end of each packet.

The core decrements this field every time a packet is read from the RxFIFO and written to the external memory.

OTG_FS device endpoint-x transfer size register (OTG_FS_DIEPTSIZx)
(x = 1..3, where x = Endpoint_number)

Address offset: 0x910 + 0x20 * x

Reset value: 0x0000 0000

The application must modify this register before enabling the endpoint. Once the endpoint is enabled using the Endpoint enable bit in the OTG_FS_DIEPCTLx registers (EPENA bit in OTG_FS_DIEPCTLx), the core modifies this register. The application can only read this register once the core has cleared the Endpoint enable bit.

Bits 31:29 Reserved, must be kept at reset value.

Bit 28:19 PKTCNT: Packet count

Indicates the total number of USB packets that constitute the Transfer Size amount of data for this endpoint.

This field is decremented every time a packet (maximum size or short packet) is read from the TxFIFO.

Bits 18:0 XFRSIZ: Transfer size

This field contains the transfer size in bytes for the current endpoint. The core only interrupts the application after it has exhausted the transfer size amount of data. The transfer size can be set to the maximum packet size of the endpoint, to be interrupted at the end of each packet.

The core decrements this field every time a packet from the external memory is written to the TxFIFO.

OTG_FS device IN endpoint transmit FIFO status register
(OTG_FS_DTXFSTSx) (x = 0..3, where x = Endpoint_number)

Address offset for IN endpoints: \( 0x918 + 0x20 * x \)

This read-only register contains the free space information for the Device IN endpoint TxFIFO.

31:16 Reserved, must be kept at reset value.

15:0 INEPTFSAV : IN endpoint TxFIFO space available

Indicates the amount of free space available in the Endpoint TxFIFO.
Values are in terms of 32-bit words:

• 0x0: Endpoint TxFIFO is full
• 0x1: 1 word available
• 0x2: 2 words available
• 0xn: n words available
• Others: Reserved

OTG_FS device OUT endpoint-x transfer size register (OTG_FS_DOEPTSIZx)
(x = 1..3, where x = Endpoint_number)

Address offset: \( 0xB10 + 0x20 * x \)

Reset value: 0x0000 0000

The application must modify this register before enabling the endpoint. Once the endpoint is enabled using Endpoint Enable bit of the OTG_FS_DOEPCTLx registers (EPENA bit in OTG_FS_DOEPCTLx), the core modifies this register. The application can only read this register once the core has cleared the Endpoint enable bit.

Bit 31 Reserved, must be kept at reset value.

Bits 30:29 RXDPID : Received data PID

Applies to isochronous OUT endpoints only.
This is the data PID received in the last packet for this endpoint.

• 00: DATA0
• 01: DATA2
• 10: DATA1
• 11: MDATA

Applies to control OUT Endpoints only.

This field specifies the number of back-to-back SETUP data packets the endpoint can receive.

01: 1 packet

10: 2 packets

11: 3 packets

Indicates the total number of USB packets that constitute the Transfer Size amount of data for this endpoint.

This field is decremented every time a packet (maximum size or short packet) is written to the RxFIFO.

This field contains the transfer size in bytes for the current endpoint. The core only interrupts the application after it has exhausted the transfer size amount of data. The transfer size can be set to the maximum packet size of the endpoint, to be interrupted at the end of each packet.

The core decrements this field every time a packet is read from the RxFIFO and written to the external memory.

22.16.5 OTG_FS power and clock gating control register (OTG_FS_PCGCTL)

Address offset: 0xE00

Reset value: 0x0000 0000

This register is available in host and device modes.

Bit 31:5 Reserved, must be kept at reset value.

Indicates that the PHY has been suspended. This bit is updated once the PHY is suspended after the application has set the STPPCLK bit (bit 0).

Bits 3:2 Reserved, must be kept at reset value.

The application sets this bit to gate HCLK to modules other than the AHB Slave and Master and wake-up logic when the USB is suspended or the session is not valid. The application clears this bit when the USB is resumed or a new session starts.

The application sets this bit to stop the PHY clock when the USB is suspended, the session is not valid, or the device is disconnected. The application clears this bit when the USB is resumed or a new session starts.

22.16.6 OTG_FS register map

The table below gives the USB OTG register map and reset values.

Table 135. OTG_FS register map and reset values

Table 135. OTG_FS register map and reset values (continued)

Table 135. OTG_FS register map and reset values (continued)

Table 135. OTG_FS register map and reset values (continued)

Table 135. OTG_FS register map and reset values (continued)