16. Flexible static memory controller (FSMC)

16.1 Introduction

The flexible static memory controller (FSMC) includes two memory controllers:

• • The NOR/PSRAM memory controller
• • The NAND memory controller

This memory controller is also named flexible memory controller (FMC).

16.2 FMC main features

The FMC functional block makes the interface with: synchronous and asynchronous static memories, and NAND flash memory. Its main purposes are:

• • to translate AHB transactions into the appropriate external device protocol
• • to meet the access time requirements of the external memory devices

All external memories share the addresses, data and control signals with the controller. Each external device is accessed by means of a unique chip select. The FMC performs only one access at a time to an external device.

The main features of the FMC controller are the following:

• • Interface with static-memory mapped devices including:
  • – Static random access memory (SRAM)
  • – NOR flash memory/OneNAND flash memory
  • – PSRAM (4 memory banks)
  • – NAND flash memory with ECC hardware to check up to 8 Kbytes of data
• • Interface with parallel LCD modules, supporting Intel 8080 and Motorola 6800 modes.
• • Burst mode support for faster access to synchronous devices such as NOR flash memory, PSRAM)
• • Programmable continuous clock output for asynchronous and synchronous accesses
• • 8-,16-bit wide data bus
• • Independent chip select control for each memory bank
• • Independent configuration for each memory bank
• • Write enable and byte lane select outputs for use with PSRAM, SRAM devices
• • External asynchronous wait control
• • Write FIFO with 16 x32-bit depth

The Write FIFO is common to all memory controllers and consists of:

• • a Write Data FIFO which stores the AHB data to be written to the memory (up to 32 bits) plus one bit for the AHB transfer (burst or not sequential mode)
• • a Write Address FIFO which stores the AHB address (up to 28 bits) plus the AHB data size (up to 2 bits). When operating in burst mode, only the start address is stored except when crossing a page boundary (for PSRAM). In this case, the AHB burst is broken into two FIFO entries.

The Write FIFO can be disabled by setting the WFDIS bit in the FMC_BCR1 register (only for STM32L49x/L4Ax devices).

At startup the FMC pins must be configured by the user application. The FMC I/O pins which are not used by the application can be used for other purposes.

The FMC registers that define the external device type and associated characteristics are usually set at boot time and do not change until the next reset or power-up. However, the settings can be changed at any time.

16.3 FMC block diagram

The FMC consists of the following main blocks:

• • The AHB interface (including the FMC configuration registers)
• • The NOR flash/PSRAM/SRAM controller
• • The external device interface
• • The NAND flash controller

The block diagram is shown in the figure below.

Figure 36. FMC block diagram

16.4 AHB interface

The AHB slave interface allows internal CPUs and other bus master peripherals to access the external memories.

AHB transactions are translated into the external device protocol. In particular, if the selected external memory is 16- or 8-bit wide, 32-bit wide transactions on the AHB are split into consecutive 16- or 8-bit accesses. The FMC chip select (FMC_NEx) does not toggle between the consecutive accesses except in case of Access mode D when the Extended mode is enabled.

The FMC generates an AHB error in the following conditions:

• • When reading or writing to a FMC bank (Bank 1 to 4) which is not enabled.
• • When reading or writing to the NOR flash bank while the FACCEN bit is reset in the FMC_BCRx register.

The effect of an AHB error depends on the AHB master which has attempted the R/W access:

• • If the access has been attempted by the Cortex ^® -M4 CPU, a hard fault interrupt is generated.
• • If the access has been performed by a DMA controller, a DMA transfer error is generated and the corresponding DMA channel is automatically disabled.

The AHB clock (HCLK) is the reference clock for the FMC.

16.4.1 Supported memories and transactions

General transaction rules

The requested AHB transaction data size can be 8-, 16- or 32-bit wide whereas the accessed external device has a fixed data width. This may lead to inconsistent transfers.

Therefore, some simple transaction rules must be followed:

• • AHB transaction size and memory data size are equal
  There is no issue in this case.
• • AHB transaction size is greater than the memory size:

In this case, the FMC splits the AHB transaction into smaller consecutive memory accesses to meet the external data width. The FMC chip select (FMC_NEx) does not toggle between the consecutive accesses.

• • AHB transaction size is smaller than the memory size:

The transfer may or not be consistent depending on the type of external device:

• – Accesses to devices that have the byte select feature (SRAM, ROM, PSRAM)

In this case, the FMC allows read/write transactions and accesses to the right data through its byte lanes NBL[1:0].

Bytes to be written are addressed by NBL[1:0].

All memory bytes are read (NBL[1:0] are driven low during read transaction) and the useless ones are discarded.

• – Accesses to devices that do not have the byte select feature (NOR and NAND flash memories)

This situation occurs when a byte access is requested to a 16-bit wide flash memory. Since the device cannot be accessed in Byte mode (only 16-bit words can be read/written from/to the flash memory), Write transactions and Read transactions are allowed (the controller reads the entire 16-bit memory word and uses only the required byte).

Wrap support for NOR flash/PSRAM

Wrap burst mode for synchronous memories is not supported. The memories must be configured in Linear burst mode of undefined length.

Configuration registers

The FMC can be configured through a set of registers. Refer to Section 16.6.6 , for a detailed description of the NOR flash/PSRAM controller registers. Refer to Section 16.7.7 , for a detailed description of the NAND flash registers.

16.5 External device address mapping

From the FMC point of view, the external memory is divided into fixed-size banks of 256 Mbytes each (see Figure 37 ):

• • Bank 1 used to address up to 4 NOR flash memory or PSRAM devices. This bank is split into 4 NOR/PSRAM subbanks with 4 dedicated chip selects, as follows:
  • – Bank 1 - NOR/PSRAM 1
  • – Bank 1 - NOR/PSRAM 2
  • – Bank 1 - NOR/PSRAM 3
  • – Bank 1 - NOR/PSRAM 4
• • Bank 3 used to address NAND flash memory devices. The MPU memory attribute for this space must be reconfigured by software to Device.

For each bank the type of memory to be used can be configured by the user application through the Configuration register.

Figure 37. FMC memory banks

16.5.1 NOR/PSRAM address mapping

HADDR[27:26] bits are used to select one of the four memory banks as shown in Table 63 .

Table 63. NOR/PSRAM bank selection

1. 1. HADDR are internal AHB address lines that are translated to external memory.

The HADDR[25:0] bits contain the external memory address. Since HADDR is a byte address whereas the memory is addressed at word level, the address actually issued to the memory varies according to the memory data width, as shown in the following table.

Table 64. NOR/PSRAM External memory address

1. 1. In case of a 16-bit external memory width, the FMC internally uses HADDR[25:1] to generate the address for external memory FMC_A[24:0].
   Whatever the external memory width, FMC_A[0] must be connected to external memory address A[0].

16.5.2 NAND flash memory address mapping

The NAND bank is divided into memory areas as indicated in Table 65 .

Table 65. NAND memory mapping and timing registers

For NAND flash memory, the common and attribute memory spaces are subdivided into three sections (see in Table 66 below) located in the lower 256 Kbytes:

• • Data section (first 64 Kbytes in the common/attribute memory space)
• • Command section (second 64 Kbytes in the common / attribute memory space)
• • Address section (next 128 Kbytes in the common / attribute memory space)

Table 66. NAND bank selection

The application software uses the 3 sections to access the NAND flash memory:

• • To sending a command to NAND flash memory , the software must write the command value to any memory location in the command section.
• • To specify the NAND flash address that must be read or written , the software must write the address value to any memory location in the address section. Since an address can be 4 or 5 bytes long (depending on the actual memory size), several consecutive write operations to the address section are required to specify the full address.
• • To read or write data , the software reads or writes the data from/to any memory location in the data section.

Since the NAND flash memory automatically increments addresses, there is no need to increment the address of the data section to access consecutive memory locations.

16.6 NOR flash/PSRAM controller

The FMC generates the appropriate signal timings to drive the following types of memories:

• • Asynchronous SRAM and ROM
  • – 8 bits
  • – 16 bits
• • PSRAM (CellularRAM™)
  • – Asynchronous mode
  • – Burst mode for synchronous accesses
  • – Multiplexed or non-multiplexed
• • NOR flash memory
  • – Asynchronous mode
  • – Burst mode for synchronous accesses
  • – Multiplexed or non-multiplexed

The FMC outputs a unique chip select signal, NE[4:1], per bank. All the other signals (addresses, data and control) are shared.

The FMC supports a wide range of devices through a programmable timings among which:

• • Programmable wait states (up to 15)
• • Programmable bus turnaround cycles (up to 15)
• • Programmable output enable and write enable delays (up to 15)
• • Independent read and write timings and protocol to support the widest variety of memories and timings
• • Programmable continuous clock (FMC_CLK) output.

The FMC Clock (FMC_CLK) is a submultiple of the HCLK clock. It can be delivered to the selected external device either during synchronous accesses only or during asynchronous and synchronous accesses depending on the CCKEN bit configuration in the FMC_BCR1 register:

• • If the CCKEN bit is reset, the FMC generates the clock (CLK) only during synchronous accesses (Read/write transactions).
• • If the CCKEN bit is set, the FMC generates a continuous clock during asynchronous and synchronous accesses. To generate the FMC_CLK continuous clock, Bank 1 must

be configured in Synchronous mode (see Section 16.6.6: NOR/PSRAM controller registers ). Since the same clock is used for all synchronous memories, when a continuous output clock is generated and synchronous accesses are performed, the AHB data size has to be the same as the memory data width (MWID) otherwise the FMC_CLK frequency is changed depending on AHB data transaction (refer to Section 16.6.5: Synchronous transactions for FMC_CLK divider ratio formula).

The size of each bank is fixed and equal to 64 Mbytes. Each bank is configured through dedicated registers (see Section 16.6.6: NOR/PSRAM controller registers ).

The programmable memory parameters include access times (see Table 67 ) and support for wait management (for PSRAM and NOR flash accessed in Burst mode).

Table 67. Programmable NOR/PSRAM access parameters

16.6.1 External memory interface signals

Table 68 , Table 69 and Table 70 list the signals that are typically used to interface with NOR flash memory, SRAM and PSRAM.

Note: The prefix “N” identifies the signals that are active low.

NOR flash memory, non-multiplexed I/Os

Table 68. Non-multiplexed I/O NOR flash memory

The maximum capacity is 512 Mbits (26 address lines).

NOR flash memory, 16-bit multiplexed I/Os

The maximum capacity is 512 Mbits.

PSRAM/SRAM, non-multiplexed I/Os

The maximum capacity is 512 Mbits.

PSRAM, 16-bit multiplexed I/Os

Table 71. 16-Bit multiplexed I/O PSRAM

The maximum capacity is 512 Mbits (26 address lines).

16.6.2 Supported memories and transactions

Table 72 below shows an example of the supported devices, access modes and transactions when the memory data bus is 16-bit wide for NOR flash memory, PSRAM and SRAM. The transactions not allowed (or not supported) by the FMC are shown in gray in this example.

Table 72. NOR flash/PSRAM: example of supported memories and transactions

Table 72. NOR flash/PSRAM: example of supported memories and transactions (continued)

16.6.3 General timing rules

Signals synchronization

• All controller output signals change on the rising edge of the internal clock (HCLK)
• In Synchronous mode (read or write), all output signals change on the rising edge of HCLK. Whatever the CLKDIV value, all outputs change as follows:
  • NOEL/NWEL/ NEL/NADVL/ NADVH /NBLL/ Address valid outputs change on the falling edge of FMC_CLK clock.
  • NOEH/ NWEH / NEH/ NOEH/NBLH/ Address invalid outputs change on the rising edge of FMC_CLK clock.

16.6.4 NOR flash/PSRAM controller asynchronous transactions

Asynchronous static memories (NOR flash, PSRAM, SRAM)

• Signals are synchronized by the internal clock HCLK. This clock is not issued to the memory

• • The FMC always samples the data before de-asserting the NOE signal. This guarantees that the memory data hold timing constraint is met (minimum Chip Enable high to data transition is usually 0 ns)
• • If the Extended mode is enabled (EXTMOD bit is set in the FMC_BCRx register), up to four extended modes (A, B, C and D) are available. It is possible to mix A, B, C and D modes for read and write operations. For example, read operation can be performed in mode A and write in mode B.
• • If the Extended mode is disabled (EXTMOD bit is reset in the FMC_BCRx register), the FMC can operate in mode 1 or mode 2 as follows:
  • – Mode 1 is the default mode when SRAM/PSRAM memory type is selected (MTYP = 0x0 or 0x01 in the FMC_BCRx register)
  • – Mode 2 is the default mode when NOR memory type is selected (MTYP = 0x10 in the FMC_BCRx register).

Mode 1 - SRAM/PSRAM (CRAM)

The next figures show the read and write transactions for the supported modes followed by the required configuration of FMC_BCRx, and FMC_BTRx/FMC_BWTRx registers.

Figure 38. Mode 1 read access waveforms

Figure 39. Mode 1 write access waveforms

The one HCLK cycle at the end of the write transaction helps guarantee the address and data hold time after the NWE rising edge. Due to the presence of this HCLK cycle, the DATAST value must be greater than zero (DATAST > 0).

Table 73. FMC_BCRx bitfields (mode 1)

Mode A - SRAM/PSRAM (CRAM) OE toggling

Figure 40. Mode A read access waveforms

1. 1. NBL[1:0] are driven low during the read access

Figure 41. Mode A write access waveforms

The differences compared with Mode 1 are the toggling of NOE and the independent read and write timings.

Table 75. FMC_BCRx bitfields (mode A)

Table 76. FMC_BTRx bitfields (mode A)

Table 77. FMC_BWTRx bitfields (mode A)

Mode 2/B - NOR flash

Figure 42. Mode 2 and mode B read access waveforms

Figure 43. Mode 2 write access waveforms

Figure 44. Mode B write access waveforms

The differences with mode 1 are the toggling of NWE and the independent read and write timings when extended mode is set (mode B).

Table 80. FMC_BWTRx bitfields (mode 2/B)

Note: The FMC_BWTRx register is valid only if the Extended mode is set (mode B), otherwise its content is don’t care.

Mode C - NOR flash - OE toggling

Figure 45. Mode C read access waveforms

Figure 46. Mode C write access waveforms

The differences compared with mode 1 are the toggling of NOE and the independent read and write timings.

Table 81. FMC_BCRx bitfields (mode C)

Mode D - asynchronous access with extended address

Figure 47. Mode D read access waveforms

Figure 48. Mode D write access waveforms

The differences with mode 1 are the toggling of NOE that goes on toggling after NADV changes and the independent read and write timings.

Table 84. FMC_BCRx bitfields (mode D)

Table 85. FMC_BTRx bitfields (mode D)

Table 86. FMC_BWTRx bitfields (mode D)

Muxed mode - multiplexed asynchronous access to NOR flash memory

Figure 49. Muxed read access waveforms

Figure 50. Muxed write access waveforms

The difference with mode D is the drive of the lower address byte(s) on the data bus.

Table 87. FMC_BCRx bitfields (Muxed mode)

WAIT management in asynchronous accesses

If the asynchronous memory asserts the WAIT signal to indicate that it is not yet ready to accept or to provide data, the ASYNCWAIT bit has to be set in FMC_BCRx register.

If the WAIT signal is active (high or low depending on the WAITPOL bit), the second access phase (Data setup phase), programmed by the DATAST bits, is extended until WAIT becomes inactive. Unlike the data setup phase, the first access phases (Address setup and Address hold phases), programmed by the ADDSET and ADDHLD bits, are not WAIT sensitive and so they are not prolonged.

The data setup phase must be programmed so that WAIT can be detected 4 HCLK cycles before the end of the memory transaction. The following cases must be considered:

1. 1. The memory asserts the WAIT signal aligned to NOE/NWE which toggles:

1. 2. The memory asserts the WAIT signal aligned to NEx (or NOE/NWE not toggling):
   if

then:

otherwise

where \( \text{max\_wait\_assertion\_time} \) is the maximum time taken by the memory to assert the WAIT signal once NEx/NOE/NWE is low.

Figure 51 and Figure 52 show the number of HCLK clock cycles that are added to the memory access phase after WAIT is released by the asynchronous memory (independently of the above cases).

Figure 51. Asynchronous wait during a read access waveforms

1. 1. NWAIT polarity depends on WAITPOL bit setting in FMC_BCRx register.

Figure 52. Asynchronous wait during a write access waveforms

1. NWAIT polarity depends on WAITPOL bit setting in FMC_BCRx register.

16.6.5 Synchronous transactions

The memory clock, FMC_CLK, is a submultiple of HCLK. It depends on the value of CLKDIV and the MWID/ AHB data size, following the formula given below:

Whatever MWID size: 16 or 8-bit, the FMC_CLK divider ratio is always defined by the programmed CLKDIV value.

Example:

• • If CLKDIV=1, MWID = 16 bits, AHB data size=8 bits, FMC_CLK=HCLK/2.

NOR flash memories specify a minimum time from NADV assertion to CLK high. To meet this constraint, the FMC does not issue the clock to the memory during the first internal clock cycle of the synchronous access (before NADV assertion). This guarantees that the rising edge of the memory clock occurs in the middle of the NADV low pulse.

Data latency versus NOR memory latency

The data latency is the number of cycles to wait before sampling the data. The DATLAT value must be consistent with the latency value specified in the NOR flash configuration register. The FMC does not include the clock cycle when NADV is low in the data latency count.

Caution: Some NOR flash memories include the NADV Low cycle in the data latency count, so that the exact relation between the NOR flash latency and the FMC DATLAT parameter can be either:

• • NOR flash latency = (DATLAT + 2) CLK clock cycles
• • or NOR flash latency = (DATLAT + 3) CLK clock cycles

Some recent memories assert NWAIT during the latency phase. In such cases DATLAT can be set to its minimum value. As a result, the FMC samples the data and waits long enough to evaluate if the data are valid. Thus the FMC detects when the memory exits latency and real data are processed.

Other memories do not assert NWAIT during latency. In this case the latency must be set correctly for both the FMC and the memory, otherwise invalid data are mistaken for good data, or valid data are lost in the initial phase of the memory access.

Single-burst transfer

When the selected bank is configured in Burst mode for synchronous accesses, if for example an AHB single-burst transaction is requested on 16-bit memories, the FMC performs a burst transaction of length 1 (if the AHB transfer is 16 bits), or length 2 (if the AHB transfer is 32 bits) and de-assert the chip select signal when the last data is strobed.

Such transfers are not the most efficient in terms of cycles compared to asynchronous read operations. Nevertheless, a random asynchronous access would first require to re-program the memory access mode, which would altogether last longer.

Cross boundary page for CellularRAM™ 1.5

CellularRAM™ 1.5 does not allow burst access to cross the page boundary. The FMC controller is used to split automatically the burst access when the memory page size is reached by configuring the CPSIZE bits in the FMC_BCR1 register following the memory page size.

Wait management

For synchronous NOR flash memories, NWAIT is evaluated after the programmed latency period, which corresponds to (DATLAT+2) CLK clock cycles.

If NWAIT is active (low level when WAITPOL = 0, high level when WAITPOL = 1), wait states are inserted until NWAIT is inactive (high level when WAITPOL = 0, low level when WAITPOL = 1).

When NWAIT is inactive, the data is considered valid either immediately (bit WAITCFG = 1) or on the next clock edge (bit WAITCFG = 0).

During wait-state insertion via the NWAIT signal, the controller continues to send clock pulses to the memory, keeping the chip select and output enable signals valid. It does not consider the data as valid.

In Burst mode, there are two timing configurations for the NOR flash NWAIT signal:

• • The flash memory asserts the NWAIT signal one data cycle before the wait state (default after reset).
• • The flash memory asserts the NWAIT signal during the wait state

The FMC supports both NOR flash wait state configurations, for each chip select, thanks to the WAITCFG bit in the FMC_BCRx registers (x = 0..3).

Figure 53. Wait configuration waveforms

Figure 54. Synchronous multiplexed read mode waveforms - NOR, PSRAM (CRAM)

1. 1. Byte lane outputs (NBL are not shown; for NOR access, they are held high, and, for PSRAM (CRAM) access, they are held low.

Figure 55. Synchronous multiplexed write mode waveforms - PSRAM (CRAM)

1. 1. The memory must issue NWAIT signal one cycle in advance, accordingly WAITCFG must be programmed to 0.
2. 2. Byte Lane (NBL) outputs are not shown, they are held low while NEx is active.

Table 91. FMC_BCRx bitfields (Synchronous multiplexed write mode)

16.6.6 NOR/PSRAM controller registers

SRAM/NOR-flash chip-select control register for bank x (FMC_BCRx) (x = 1 to 4)

Address offset: 0x00 + 0x8 * (x - 1), (x = 1 to 4)

Reset value: 0x0000 30DB, 0x0000 30D2, 0x0000 30D2, 0x0000 30D2

This register contains the control information of each memory bank, used for SRAMs, PSRAM and NOR flash memories.

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

Bit 21 WFDIS: Write FIFO disable

This bit disables the Write FIFO used by the FMC controller.

0: Write FIFO enabled (Default after reset)

1: Write FIFO disabled

Note: This bit is reserved for STM32L47x/L48x devices.

Note: The WFDIS bit of the FMC_BCR2..4 registers is don't care. It is only enabled through the FMC_BCR1 register.

Bit 20 CCLKEN: Continuous clock enable

This bit enables the FMC_CLK clock output to external memory devices.

0: The FMC_CLK is only generated during the synchronous memory access (read/write transaction). The FMC_CLK clock ratio is specified by the programmed CLKDIV value in the FMC_BCRx register (default after reset).

1: The FMC_CLK is generated continuously during asynchronous and synchronous access. The FMC_CLK clock is activated when the CCLKEN is set.

Note: The CCLKEN bit of the FMC_BCR2..4 registers is don't care. It is only enabled through the FMC_BCR1 register. Bank 1 must be configured in Synchronous mode to generate the FMC_CLK continuous clock.

Note: If CCLKEN bit is set, the FMC_CLK clock ratio is specified by CLKDIV value in the FMC_BTR1 register. CLKDIV in FMC_BWTR1 is don't care.

Note: If the Synchronous mode is used and CCLKEN bit is set, the synchronous memories connected to other banks than Bank 1 are clocked by the same clock (the CLKDIV value in the FMC_BTR2..4 and FMC_BWTR2..4 registers for other banks has no effect.)

Bit 19 CBURSTRW: Write burst enable

For PSRAM (CRAM) operating in Burst mode, the bit enables synchronous accesses during write operations. The enable bit for synchronous read accesses is the BURSTEN bit in the FMC_BCRx register.

0: Write operations are always performed in Asynchronous mode.

1: Write operations are performed in Synchronous mode.

These are used for CellularRAM™ 1.5 which does not allow burst access to cross the address boundaries between pages. When these bits are configured, the FMC controller splits automatically the burst access when the memory page size is reached (refer to memory datasheet for page size).

000: No burst split when crossing page boundary (default after reset)

001: 128 bytes

010: 256 bytes

011: 512 bytes

100: 1024 bytes

Others: Reserved, must not be used

This bit enables/disables the FMC to use the wait signal even during an asynchronous protocol.

0: NWAIT signal is not taken in to account when running an asynchronous protocol (default after reset).

1: NWAIT signal is taken in to account when running an asynchronous protocol.

This bit enables the FMC to program the write timings for non multiplexed asynchronous accesses inside the FMC_BWTR register, thus resulting in different timings for read and write operations.

0: values inside FMC_BWTR register are not taken into account (default after reset)

1: values inside FMC_BWTR register are taken into account

Note: When the Extended mode is disabled, the FMC can operate in mode 1 or mode 2 as follows:

• – Mode 1 is the default mode when the SRAM/PSRAM memory type is selected (MTYP = 0x0 or 0x01)
• – Mode 2 is the default mode when the NOR memory type is selected (MTYP = 0x10).

This bit enables/disables wait-state insertion via the NWAIT signal when accessing the memory in Synchronous mode.

0: NWAIT signal is disabled (its level not taken into account, no wait state inserted after the programmed flash latency period).

1: NWAIT signal is enabled (its level is taken into account after the programmed latency period to insert wait states if asserted) (default after reset).

This bit indicates whether write operations are enabled/disabled in the bank by the FMC.

0: Write operations are disabled in the bank by the FMC, an AHB error is reported.

1: Write operations are enabled for the bank by the FMC (default after reset).

The NWAIT signal indicates whether the data from the memory are valid or if a wait state must be inserted when accessing the memory in Synchronous mode. This configuration bit determines if NWAIT is asserted by the memory one clock cycle before the wait state or during the wait state:

0: NWAIT signal is active one data cycle before wait state (default after reset).

1: NWAIT signal is active during wait state (not used for PSRAM).

Bit 10 Reserved, must be kept at reset value.

Defines the polarity of the wait signal from memory used for either in Synchronous or Asynchronous mode.

0: NWAIT active low (default after reset)

1: NWAIT active high

This bit enables/disables synchronous accesses during read operations. It is valid only for synchronous memories operating in Burst mode.

0: Burst mode disabled (default after reset). Read accesses are performed in Asynchronous mode.

1: Burst mode enable. Read accesses are performed in Synchronous mode.

Bit 7 Reserved, must be kept at reset value.

Enables NOR flash memory access operations.

0: Corresponding NOR flash memory access is disabled.

1: Corresponding NOR flash memory access is enabled (default after reset).

Defines the external memory device width, valid for all type of memories.

00: 8 bits

01: 16 bits (default after reset)

10: reserved

11: reserved

Defines the type of external memory attached to the corresponding memory bank.

00: SRAM (default after reset for Bank 2...4)

01: PSRAM (CRAM)

10: NOR flash/OneNAND flash (default after reset for Bank 1)

11: reserved

When this bit is set, the address and data values are multiplexed on the data bus, valid only with NOR and PSRAM memories:

0: Address/data non multiplexed

1: Address/data multiplexed on databus (default after reset)

Enables the memory bank. After reset Bank1 is enabled, all others are disabled. Accessing a disabled bank causes an ERROR on AHB bus.

0: Corresponding memory bank is disabled.

1: Corresponding memory bank is enabled.

Address offset: \( 0x04 + 0x8 * (x - 1) \) , ( \( x = 1 \) to \( 4 \) )

Reset value: 0x0FFF FFFF

This register contains the control information of each memory bank, used for SRAMs, PSRAM and NOR flash memories. If the EXTMOD bit is set in the FMC_BCRx register, then this register is partitioned for write and read access, that is, 2 registers are available: one to

configure read accesses (this register) and one to configure write accesses (FMC_BWTRx registers).

Bits 31:30 Reserved, must be kept at reset value.

Bits 29:28 ACCMOD[1:0] : Access mode

Specifies the asynchronous access modes as shown in the timing diagrams. These bits are taken into account only when the EXTMOD bit in the FMC_BCRx register is 1.

00: Access mode A

01: Access mode B

10: Access mode C

11: Access mode D

Bits 27:24 DATLAT[3:0] : (see note below bit descriptions): Data latency for synchronous memory

For synchronous access with read/write Burst mode enabled (BURSTEN / CBURSTRW bits set), defines the number of memory clock cycles (+2) to issue to the memory before reading/writing the first data:

This timing parameter is not expressed in HCLK periods, but in FMC_CLK periods.

For asynchronous access, this value is don't care.

0000: Data latency of 2 CLK clock cycles for first burst access

1111: Data latency of 17 CLK clock cycles for first burst access (default value after reset)

Bits 23:20 CLKDIV[3:0] : Clock divide ratio (for FMC_CLK signal)

Defines the period of FMC_CLK clock output signal, expressed in number of HCLK cycles:

0000: Reserved

0001: FMC_CLK period = 2 × HCLK periods

0010: FMC_CLK period = 3 × HCLK periods

1111: FMC_CLK period = 16 × HCLK periods (default value after reset)

In asynchronous NOR flash, SRAM or PSRAM accesses, this value is don't care.

Note: Refer to Section 16.6.5: Synchronous transactions for FMC_CLK divider ratio formula

These bits are written by software to add a delay at the end of a write-to-read (and read-to-write) transaction. This delay enables to match the minimum time between consecutive transactions ( \( t_{EHEL} \) from NEx high to NEx low) and the maximum time needed by the memory to free the data bus after a read access ( \( t_{EHQZ} \) ). The programmed bus turnaround delay is inserted between an asynchronous read (muxed or mode D) or write transaction and any other asynchronous /synchronous read or write to or from a static bank. The bank can be the same or different in case of read, in case of write the bank can be different except for muxed or mode D.

In some cases, whatever the programmed BUSTURN values, the bus turnaround delay is fixed

as follows:

• • The bus turnaround delay is not inserted between two consecutive asynchronous write transfers to the same static memory bank except for muxed mode and mode D.
• • There is a bus turnaround delay of 1 HCLK clock cycle between:
  • –Two consecutive asynchronous read transfers to the same static memory bank except for muxed mode and mode D.
  • –An asynchronous read to an asynchronous or synchronous write to any static bank or dynamic bank except for muxed mode and mode D.
  • –An asynchronous (modes 1, 2, A, B or C) read and a read from another static bank.
• • There is a bus turnaround delay of 2 HCLK clock cycle between:
  • –Two consecutive synchronous writes (burst or single) to the same bank.
  • –A synchronous write (burst or single) access and an asynchronous write or read transfer to or from static memory bank (the bank can be the same or different for the case of read).
  • –Two consecutive synchronous reads (burst or single) followed by any synchronous/asynchronous read or write from/to another static memory bank.
• • There is a bus turnaround delay of 3 HCLK clock cycle between:
  • –Two consecutive synchronous writes (burst or single) to different static bank.
  • –A synchronous write (burst or single) access and a synchronous read from the same or a different bank.

0000: BUSTURN phase duration = 0 HCLK clock cycle added

...

1111: BUSTURN phase duration = 15 x HCLK clock cycles added (default value after reset)

These bits are written by software to define the duration of the data phase (refer to Figure 38 to Figure 50 ), used in asynchronous accesses:

0000 0000: Reserved

0000 0001: DATAST phase duration = 1 × HCLK clock cycles

0000 0010: DATAST phase duration = 2 × HCLK clock cycles

...

1111 1111: DATAST phase duration = 255 × HCLK clock cycles (default value after reset)

For each memory type and access mode data-phase duration, refer to the respective figure ( Figure 38 to Figure 50 ).

Example: Mode 1, write access, DATAST=1: Data-phase duration= DATAST+1 = 2 HCLK clock cycles.

Note: In synchronous accesses, this value is don't care.

These bits are written by software to define the duration of the address hold phase (refer to Figure 38 to Figure 50 ), used in mode D or multiplexed accesses:

0000: Reserved

0001: ADDHLD phase duration = 1 × HCLK clock cycle

0010: ADDHLD phase duration = 2 × HCLK clock cycle

...

1111: ADDHLD phase duration = 15 × HCLK clock cycles (default value after reset)

For each access mode address-hold phase duration, refer to the respective figure ( Figure 38 to Figure 50 ).

Note: In synchronous accesses, this value is not used, the address hold phase is always 1 memory clock period duration.

These bits are written by software to define the duration of the address setup phase (refer to Figure 38 to Figure 50 ), used in SRAMs, ROMs, asynchronous NOR flash and PSRAM:

0000: ADDSET phase duration = 0 × HCLK clock cycle

...

1111: ADDSET phase duration = 15 × HCLK clock cycles (default value after reset)

For each access mode address setup phase duration, refer to the respective figure ( Figure 38 to Figure 50 ).

Note: In synchronous accesses, this value is don't care.

In Muxed mode or mode D, the minimum value for ADDSET is 1.

In mode 1 and PSRAM memory, the minimum value for ADDSET is 1.

Note: PSRAMs (CRAMs) have a variable latency due to internal refresh. Therefore these memories issue the NWAIT signal during the whole latency phase to prolong the latency as needed. With PSRAMs (CRAMs) the filled DATLAT must be set to 0, so that the FMC exits its latency phase soon and starts sampling NWAIT from memory, then starts to read or write when the memory is ready. This method can be used also with the latest generation of synchronous flash memories that issue the NWAIT signal, unlike older flash memories (check the datasheet of the specific flash memory being used).

SRAM/NOR-flash write timing registers x (FMC_BWTRx)

Address offset: 0x104 + 0x8 * (x - 1), (x = 1 to 4)

Reset value: 0x0FFF FFFF

This register contains the control information of each memory bank. It is used for SRAMs, PSRAMs and NOR flash memories. When the EXTMOD bit is set in the FMC_BCRx register, then this register is active for write access.

Bits 31:30 Reserved, must be kept at reset value.

Bits 29:28 ACCMOD[1:0] : Access mode.

Specifies the asynchronous access modes as shown in the next timing diagrams. These bits are taken into account only when the EXTMOD bit in the FMC_BCRx register is 1.

00: Access mode A

01: Access mode B

10: Access mode C

11: Access mode D

Bits 27:20 Reserved, must be kept at reset value.

Bits 19:16 BUSTURN[3:0] : Bus turnaround phase duration

The programmed bus turnaround delay is inserted between an asynchronous write transfer and any other asynchronous /synchronous read or write transfer to or from a static bank. The bank can be the same or different in case of read, in case of write the bank can be different except for muxed or mode D.

In some cases, whatever the programmed BUSTURN values, the bus turnaround delay is fixed as follows:

• • The bus turnaround delay is not inserted between two consecutive asynchronous write transfers to the same static memory bank except for muxed and D modes.
• • There is a bus turnaround delay of 2 HCLK clock cycle between:
  • –Two consecutive synchronous writes (burst or single) to the same bank.
  • –A synchronous write (burst or single) transfer and an asynchronous write or read transfer to or from static memory bank.
• • There is a bus turnaround delay of 3 HCLK clock cycle between:
  • –Two consecutive synchronous writes (burst or single) to different static bank.
  • –A synchronous write (burst or single) transfer and a synchronous read from the same or a different bank.

0000: BUSTURN phase duration = 0 HCLK clock cycle added

...

1111: BUSTURN phase duration = 15 HCLK clock cycles added (default value after reset)

Bits 15:8 DATAST[7:0] : Data-phase duration.

These bits are written by software to define the duration of the data phase (refer to Figure 38 to Figure 50 ), used in asynchronous SRAM, PSRAM and NOR flash memory accesses:

0000 0000: Reserved

0000 0001: DATAST phase duration = 1 × HCLK clock cycles

0000 0010: DATAST phase duration = 2 × HCLK clock cycles

...

1111 1111: DATAST phase duration = 255 × HCLK clock cycles (default value after reset)

Bits 7:4 ADDHLD[3:0] : Address-hold phase duration.

These bits are written by software to define the duration of the address hold phase (refer to Figure 47 to Figure 50 ), used in asynchronous multiplexed accesses:

0000: Reserved

0001: ADDHLD phase duration = 1 × HCLK clock cycle

0010: ADDHLD phase duration = 2 × HCLK clock cycle

...

1111: ADDHLD phase duration = 15 × HCLK clock cycles (default value after reset)

Note: In synchronous NOR flash accesses, this value is not used, the address hold phase is always 1 flash clock period duration.

Bits 3:0 ADDSET[3:0] : Address setup phase duration.

These bits are written by software to define the duration of the address setup phase in HCLK cycles (refer to Figure 38 to Figure 50 ), used in asynchronous accesses:

0000: ADDSET phase duration = 0 × HCLK clock cycle

...

1111: ADDSET phase duration = 15 × HCLK clock cycles (default value after reset)

Note: In synchronous accesses, this value is not used, the address setup phase is always 1 flash clock period duration. In muxed mode, the minimum ADDSET value is 1.

16.7 NAND flash controller

The FMC generates the appropriate signal timings to drive the following types of device:

• • 8- and 16-bit NAND flash memories

The NAND bank is configured through dedicated registers ( Section 16.7.7 ). The programmable memory parameters include access timings (shown in Table 93 ) and ECC configuration.

Table 93. Programmable NAND flash access parameters

16.7.1 External memory interface signals

The following tables list the signals that are typically used to interface NAND flash memory.

Note: The prefix “N” identifies the signals which are active low.

8-bit NAND flash memory

Table 94. 8-bit NAND flash

Theoretically, there is no capacity limitation as the FMC can manage as many address cycles as needed.

16-bit NAND flash memory

Theoretically, there is no capacity limitation as the FMC can manage as many address cycles as needed.

16.7.2 NAND flash supported memories and transactions

Table 96 shows the supported devices, access modes and transactions. Transactions not allowed (or not supported) by the NAND flash controller are shown in gray.

Table 96. Supported memories and transactions (continued)

16.7.3 Timing diagrams for NAND flash memory

The NAND flash memory bank is managed through a set of registers:

• • Control register: FMC_PCR
• • Interrupt status register: FMC_SR
• • ECC register: FMC_ECCR
• • Timing register for Common memory space: FMC_PMEM
• • Timing register for Attribute memory space: FMC_PATT

Each timing configuration register contains three parameters used to define number of HCLK cycles for the three phases of any NAND flash access, plus one parameter that defines the timing for starting driving the data bus when a write access is performed.

Figure 56 shows the timing parameter definitions for common memory accesses, knowing that Attribute memory space access timings are similar.

Figure 56. NAND flash controller waveforms for common memory access

1. 1. NOE remains high (inactive) during write accesses. NWE remains high (inactive) during read accesses.
2. 2. For write access, the hold phase delay is (MEMHOLD) HCLK cycles and for read access is (MEMHOLD + 2) HCLK cycles.

16.7.4 NAND flash operations

The command latch enable (CLE) and address latch enable (ALE) signals of the NAND flash memory device are driven by address signals from the FMC controller. This means that to send a command or an address to the NAND flash memory, the CPU has to perform a write to a specific address in its memory space.

A typical page read operation from the NAND flash device requires the following steps:

1. 1. Program and enable the corresponding memory bank by configuring the FMC_PCR and FMC_PMEM (and for some devices, FMC_PATT, see Section 16.7.5: NAND flash prewait functionality ) registers according to the characteristics of the NAND flash memory (PWID bits for the data bus width of the NAND flash, PTYP = 1, PWAITEN = 0 or 1 as needed, see Section 16.5.2: NAND flash memory address mapping for timing configuration).
2. 2. The CPU performs a byte write to the common memory space, with data byte equal to one flash command byte (for example 0x00 for Samsung NAND flash devices). The LE input of the NAND flash memory is active during the write strobe (low pulse on NWE), thus the written byte is interpreted as a command by the NAND flash memory. Once the command is latched by the memory device, it does not need to be written again for the following page read operations.
3. 3. The CPU can send the start address (STARTAD) for a read operation by writing four bytes (or three for smaller capacity devices), STARTAD[7:0], STARTAD[16:9], STARTAD[24:17] and finally STARTAD[25] (for 64 Mb x 8 bit NAND flash memories) in the common memory or attribute space. The ALE input of the NAND flash device is active during the write strobe (low pulse on NWE), thus the written bytes are interpreted as the start address for read operations. Using the attribute memory space makes it possible to use a different timing configuration of the FMC, which can be used to implement the prewait functionality needed by some NAND flash memories (see details in Section 16.7.5: NAND flash prewait functionality ).
4. 4. The controller waits for the NAND flash memory to be ready (R/NB signal high), before starting a new access to the same or another memory bank. While waiting, the controller holds the NCE signal active (low).
5. 5. The CPU can then perform byte read operations from the common memory space to read the NAND flash page (data field + Spare field) byte by byte.
6. 6. The next NAND flash page can be read without any CPU command or address write operation. This can be done in three different ways:
   • – by simply performing the operation described in step 5
   • – a new random address can be accessed by restarting the operation at step 3
   • – a new command can be sent to the NAND flash device by restarting at step 2

16.7.5 NAND flash prewait functionality

Some NAND flash devices require that, after writing the last part of the address, the controller waits for the R/NB signal to go low. (see Figure 57 ).

Figure 57. Access to non 'CE don't care' NAND-flash

1. 1. CPU wrote byte 0x00 at address 0x7001 0000.
2. 2. CPU wrote byte A7~A0 at address 0x7002 0000.
3. 3. CPU wrote byte A16~A9 at address 0x7002 0000.
4. 4. CPU wrote byte A24~A17 at address 0x7002 0000.
5. 5. CPU wrote byte A25 at address 0x7802 0000: FMC performs a write access using FMC_PATT timing definition, where \( ATTHOLD \geq 7 \) (providing that \( (7+1) \times HCLK = 112 \text{ ns} > t_{WB} \text{ max} \) ). This guarantees that NCE remains low until R/NB goes low and high again (only requested for NAND flash memories where NCE is not don't care).

When this functionality is required, it can be ensured by programming the MEMHOLD value to meet the \( t_{WB} \) timing. However any CPU read access to the NAND flash memory has a hold delay of \( (MEMHOLD + 2) \) HCLK cycles and CPU write access has a hold delay of \( (MEMHOLD) \) HCLK cycles inserted between the rising edge of the NWE signal and the next access.

To cope with this timing constraint, the attribute memory space can be used by programming its timing register with an ATTHOLD value that meets the \( t_{WB} \) timing, and by keeping the MEMHOLD value at its minimum value. The CPU must then use the common memory space for all NAND flash read and write accesses, except when writing the last address byte to the NAND flash device, where the CPU must write to the attribute memory space.

16.7.6 Computation of the error correction code (ECC) in NAND flash memory

The FMC NAND Card controller includes two error correction code computation hardware blocks, one per memory bank. They reduce the host CPU workload when processing the ECC by software.

These two ECC blocks are identical and associated with Bank 2 and Bank 3. As a consequence, no hardware ECC computation is available for memories connected to Bank 4.

The ECC algorithm implemented in the FMC can perform 1-bit error correction and 2-bit error detection per 256, 512, 1 024, 2 048, 4 096 or 8 192 bytes read or written from/to the NAND flash memory. It is based on the Hamming coding algorithm and consists in calculating the row and column parity.

The ECC modules monitor the NAND flash data bus and read/write signals (NCE and NWE) each time the NAND flash memory bank is active.

The ECC operates as follows:

• • When accessing NAND flash memory bank 2 or bank 3, the data present on the D[15:0] bus is latched and used for ECC computation.
• • When accessing any other address in NAND flash memory, the ECC logic is idle, and does not perform any operation. As a result, write operations to define commands or addresses to the NAND flash memory are not taken into account for ECC computation.

Once the desired number of bytes has been read/written from/to the NAND flash memory by the host CPU, the FMC_ECCR registers must be read to retrieve the computed value. Once read, they must be cleared by resetting the ECCEN bit to '0'. To compute a new data block, the ECCEN bit must be set to one in the FMC_PCR registers.

To perform an ECC computation:

1. 1. Enable the ECCEN bit in the FMC_PCR register.
2. 2. Write data to the NAND flash memory page. While the NAND page is written, the ECC block computes the ECC value.
3. 3. Read the ECC value available in the FMC_ECCR register and store it in a variable.
4. 4. Clear the ECCEN bit and then enable it in the FMC_PCR register before reading back the written data from the NAND page. While the NAND page is read, the ECC block computes the ECC value.
5. 5. Read the new ECC value available in the FMC_ECCR register.
6. 6. If the two ECC values are the same, no correction is required, otherwise there is an ECC error and the software correction routine returns information on whether the error can be corrected or not.

16.7.7 NAND flash controller registers

NAND flash control registers (FMC_PCR)

Address offset: 0x80

Reset value: 0x0000 0018

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

Bits 19:17 ECCPS[2:0] : ECC page size

Defines the page size for the extended ECC:

000: 256 bytes

001: 512 bytes

010: 1024 bytes

011: 2048 bytes

100: 4096 bytes

101: 8192 bytes

Bits 16:13 TAR[3:0] : ALE to RE delay

Sets time from ALE low to RE low in number of AHB clock cycles (HCLK).

Time is: \( t\_ar = (TAR + SET + 2) \times THCLK \) where THCLK is the HCLK clock period

0000: 1 HCLK cycle (default)

1111: 16 HCLK cycles

Note: SET is MEMSET or ATTSET according to the addressed space.

Bits 12:9 TCLR[3:0] : CLE to RE delay

Sets time from CLE low to RE low in number of AHB clock cycles (HCLK).

Time is: \( t\_clr = (TCLR + SET + 2) \times THCLK \) where THCLK is the HCLK clock period

0000: 1 HCLK cycle (default)

1111: 16 HCLK cycles

Note: SET is MEMSET or ATTSET according to the addressed space.

Bits 8:7 Reserved, must be kept at reset value.

Bit 6 ECCEN : ECC computation logic enable bit

0: ECC logic is disabled and reset (default after reset),

1: ECC logic is enabled.

Bits 5:4 PWID[1:0] : Data bus width

Defines the external memory device width.

00: 8 bits

01: 16 bits (default after reset).

10: reserved.

11: reserved.

Bit 3 PTYP : Memory type

Defines the type of device attached to the corresponding memory bank:

0: Reserved, must be kept at reset value

1: NAND flash (default after reset)

Bit 2 PBKEN : NAND flash memory bank enable bit

Enables the memory bank. Accessing a disabled memory bank causes an ERROR on AHB bus

0: Corresponding memory bank is disabled (default after reset)

1: Corresponding memory bank is enabled

Bit 1 PWAITEN : Wait feature enable bit

Enables the Wait feature for the NAND flash memory bank:

0: disabled

1: enabled

Bit 0 Reserved, must be kept at reset value.

FIFO status and interrupt register (FMC_SR)

Address offset: 0x84

Reset value: 0x0000 0040

This register contains information about the FIFO status and interrupt. The FMC features a FIFO that is used when writing to memories to transfer up to 16 words of data from the AHB.

This is used to quickly write to the FIFO and free the AHB for transactions to peripherals other than the FMC, while the FMC is draining its FIFO into the memory. One of these register bits indicates the status of the FIFO, for ECC purposes.

The ECC is calculated while the data are written to the memory. To read the correct ECC, the software must consequently wait until the FIFO is empty.

Bits 31:7 Reserved, must be kept at reset value.

Bit 6 FEMPT : FIFO empty

Read-only bit that provides the status of the FIFO

0: FIFO not empty

1: FIFO empty

Bit 5 IFEN : Interrupt falling edge detection enable bit

0: Interrupt falling edge detection request disabled

1: Interrupt falling edge detection request enabled

Bit 4 ILEN : Interrupt high-level detection enable bit

0: Interrupt high-level detection request disabled

1: Interrupt high-level detection request enabled

Bit 3 IREN : Interrupt rising edge detection enable bit

0: Interrupt rising edge detection request disabled

1: Interrupt rising edge detection request enabled

Bit 2 IFS : Interrupt falling edge status

The flag is set by hardware and reset by software.

0: No interrupt falling edge occurred

1: Interrupt falling edge occurred

Note: If this bit is written by software to 1 it is set.

Bit 1 ILS : Interrupt high-level status

The flag is set by hardware and reset by software.

0: No Interrupt high-level occurred

1: Interrupt high-level occurred

Bit 0 IRS : Interrupt rising edge status

The flag is set by hardware and reset by software.

0: No interrupt rising edge occurred

1: Interrupt rising edge occurred

Note: If this bit is written by software to 1 it is set.

Common memory space timing register (FMC_PMEM)

Address offset: 0x88

Reset value: 0xFCFC FCFC

The FMC_PMEM read/write register contains the timing information for NAND flash memory bank. This information is used to access either the common memory space of the NAND flash for command, address write access and data read/write access.

Bits 31:24 MEMHIZ[7:0] : Common memory x data bus Hi-Z time

Defines the number of HCLK clock cycles during which the data bus is kept Hi-Z after the start of a NAND flash write access to common memory space on socket. This is only valid for write transactions:

0000 0000: 1 HCLK cycle

1111 1110: 255 HCLK cycles

1111 1111: reserved.

Bits 23:16 MEMHOLD[7:0] : Common memory hold time

Defines the number of HCLK clock cycles for write access and HCLK (+2) clock cycles for read access during which the address is held (and data for write accesses) after the command is deasserted (NWE, NOE), for NAND flash read or write access to common memory space on socket x:

0000 0000: reserved.

0000 0001: 1 HCLK cycle for write access / 3 HCLK cycles for read access

1111 1110: 254 HCLK cycles for write access / 256 HCLK cycles for read access

1111 1111: reserved.

Bits 15:8 MEMWAIT[7:0] : Common memory wait time

Defines the minimum number of HCLK (+1) clock cycles to assert the command (NWE, NOE), for NAND flash read or write access to common memory space on socket. The duration of command assertion is extended if the wait signal (NWAIT) is active (low) at the end of the programmed value of HCLK:

0000 0000: reserved

0000 0001: 2HCLK cycles (+ wait cycle introduced by deasserting NWAIT)

1111 1110: 255 HCLK cycles (+ wait cycle introduced by deasserting NWAIT)

1111 1111: reserved.

Bits 7:0 MEMSET[7:0] : Common memory x setup time

Defines the number of HCLK (+1) clock cycles to set up the address before the command assertion (NWE, NOE), for NAND flash read or write access to common memory space on socket x:

0000 0000: 1 HCLK cycle

1111 1110: 255 HCLK cycles

1111 1111: reserved

Attribute memory space timing register (FMC_PATT)

Address offset: 0x8C

Reset value: 0xFCFC FCFC

The FMC_PATT read/write register contains the timing information for NAND flash memory bank. It is used for 8-bit accesses to the attribute memory space of the NAND flash for the last address write access if the timing must differ from that of previous accesses (for Ready/Busy management, refer to Section 16.7.5: NAND flash prewait functionality ).

Bits 31:24 ATTHIZ[7:0] : Attribute memory data bus Hi-Z time

Defines the number of HCLK clock cycles during which the data bus is kept in Hi-Z after the start of a NAND flash write access to attribute memory space on socket. Only valid for write transaction:

0000 0000: 0 HCLK cycle

1111 1110: 255 HCLK cycles

1111 1111: reserved.

Bits 23:16 ATTHOLD[7:0] : Attribute memory hold time

Defines the number of HCLK clock cycles for write access and HCLK (+2) clock cycles for read access during which the address is held (and data for write access) after the command deassertion (NWE, NOE), for NAND flash read or write access to attribute memory space on socket:

0000 0000: reserved

0000 0001: 1 HCLK cycle for write access / 3 HCLK cycles for read access

1111 1110: 254 HCLK cycles for write access / 256 HCLK cycles for read access

1111 1111: reserved.

Bits 15:8 ATTWAIT[7:0] : Attribute memory wait time

Defines the minimum number of HCLK (+1) clock cycles to assert the command (NWE, NOE), for NAND flash read or write access to attribute memory space on socket x. The duration for command assertion is extended if the wait signal (NWAIT) is active (low) at the end of the programmed value of HCLK:

0000 0000: reserved

0000 0001: 2 HCLK cycles (+ wait cycle introduced by deassertion of NWAIT)

1111 1110: 255 HCLK cycles (+ wait cycle introduced by deasserting NWAIT)

1111 1111: reserved.

Bits 7:0 ATTSET[7:0] : Attribute memory setup time

Defines the number of HCLK (+1) clock cycles to set up address before the command assertion (NWE, NOE), for NAND flash read or write access to attribute memory space on socket:

0000 0000: 1 HCLK cycle

1111 1110: 255 HCLK cycles

1111 1111: reserved.

ECC result registers (FMC_ECCR)

Address offset: 0x94

Reset value: 0x0000 0000

This register contains the current error correction code value computed by the ECC computation modules of the FMC NAND controller. When the CPU reads the data from a NAND flash memory page at the correct address (refer to Section 16.7.6: Computation of the error correction code (ECC) in NAND flash memory ), the data read/written from/to the NAND flash memory are processed automatically by the ECC computation module. When X bytes have been read (according to the ECCPS field in the FMC_PCR registers), the CPU must read the computed ECC value from the FMC_ECC registers. It then verifies if these computed parity data are the same as the parity value recorded in the spare area, to determine whether a page is valid, and, to correct it otherwise. The FMC_ECCR register must be cleared after being read by setting the ECCEN bit to 0. To compute a new data block, the ECCEN bit must be set to 1.

Bits 31:0 ECC[31:0] : ECC result

This field contains the value computed by the ECC computation logic. Table 97 describes the contents of these bitfields.

Table 97. ECC result relevant bits

16.7.8 FMC register map

Table 98. FMC register map and reset values

Table 98. FMC register map and reset values (continued)