STM32F4 sdram configuration

Here is some notes about playing with SDRAM. Some parts are still unclear for me but looks like all code works.

STM32 F4 family have build in FMC controller that can be configured to use SDRAM with easy.

F4 have 2 internals banks and memory ranges where SDRAM could be configured.

SDRAM parameters

STM32 SDRAM FMC params

STM32F4 SDRAM FMC(Flexible Memory Controller) have many parameters that allow to configure SDRAM, depending on chip you can have more or less memory available different clock speeds.

Struct field name Possible values Comments
SDBank BANK1,BANK2
ColumnBitsNumber 8-11 bits
RowBitsNumber 11-13 bits
MemoryDataWidth 8,16,32 bits
CASLatency 1,2,3
WriteProtection ENABLE,DISABLE
SDClockPeriod DISABLE, PERIOD2, PERIOD3 If system clock 180Mhz then CLK speeds 90Mhz or 60Mhz
ReadBurst ENABLE,DISABLE
ReadPipeDelay DELAY_0, DELAY_1, DELAY_2

Configure FMC SDRAM timings

Timing configuration configured in FMC_SDTR1 register

Struct field name RegisterPossible Values Register bit names
LoadToActiveDelay 1-16 cycles TMRD
ExitSlefRedreshDelay 1-16 cycles TXSR
SelfRefreshTime 1-16 cycles TRAS
RowCycleDelay 1-16 cycles TRC
WriteRecoveryTime 1-16 cycles TWR
RPDelay 1-16 cycles TRCD
RCDelay 1-16 cycles TRC

SDRAM initialization

Before SDRAM could start working it need to be configured and commended are sended. Command are just setting up appropriate bits and wait of 100ms.

Commands for configure SDRAM

Command Desc
FMC_SDRAM_CMD_CLK_ENABLE Configure a clock configuration enable command
FMC_SDRAM_CMD_PALL Configure a PALL (precharge all) command
FMC_SDRAM_CMD_AUTOREFRESH_MODE Configure a Auto-Refresh command
FMC_SDRAM_CMD_LOAD_MODE Program the external memory mode register
  FMC_SDRAM_CommandTypeDef Command;

    __IO uint32_t tmpmrd =0;
  /* Step 3:  Configure a clock configuration enable command */
  Command.CommandMode            = FMC_SDRAM_CMD_CLK_ENABLE;
  Command.CommandTarget          = FMC_SDRAM_CMD_TARGET_BANK1;
  Command.AutoRefreshNumber      = 1;
  Command.ModeRegisterDefinition = 0;

  /* Send the command */
  HAL_SDRAM_SendCommand(hsdram, &Command, 0x1000);

  /* Step 4: Insert 100 ms delay */
  HAL_Delay(100);

  /* Step 5: Configure a PALL (precharge all) command */ 
  Command.CommandMode            = FMC_SDRAM_CMD_PALL;
  Command.CommandTarget          = FMC_SDRAM_CMD_TARGET_BANK1;
  Command.AutoRefreshNumber      = 1;
  Command.ModeRegisterDefinition = 0;

  /* Send the command */
  HAL_SDRAM_SendCommand(hsdram, &Command, 0x1000);  

  /* Step 6 : Configure a Auto-Refresh command */ 
  Command.CommandMode            = FMC_SDRAM_CMD_AUTOREFRESH_MODE;
  Command.CommandTarget          = FMC_SDRAM_CMD_TARGET_BANK1;
  Command.AutoRefreshNumber      = 4;
  Command.ModeRegisterDefinition = 0;

  /* Send the command */
  HAL_SDRAM_SendCommand(hsdram, &Command, 0x1000);

  /* Step 7: Program the external memory mode register */
  tmpmrd = (uint32_t)SDRAM_MODEREG_BURST_LENGTH_2          |
                     SDRAM_MODEREG_BURST_TYPE_SEQUENTIAL   |
                     SDRAM_MODEREG_CAS_LATENCY_3           |
                     SDRAM_MODEREG_OPERATING_MODE_STANDARD |
                     SDRAM_MODEREG_WRITEBURST_MODE_SINGLE;

  Command.CommandMode            = FMC_SDRAM_CMD_LOAD_MODE;
  Command.CommandTarget          = FMC_SDRAM_CMD_TARGET_BANK1;
  Command.AutoRefreshNumber      = 1;
  Command.ModeRegisterDefinition = tmpmrd;

  /* Send the command */
  HAL_SDRAM_SendCommand(hsdram, &Command, 0x1000);

  HAL_SDRAM_ProgramRefreshRate(hsdram, 0x56A-20);

Command list for AS4C16M16SA

Commands
BankActive
BankPrecharge
PrechargeAll
Read
Read and AutoPrecharge
Write
Write and AutoPrecharge
Mode Register Set
No-Operation
Burst Stop
Devaise Deselect
AutoRefresh
SelfRefresh Entry
SelfRedresh Exit
Clock Suspend Mode Entry / PowerDown Mode Entry
Clock Suspend Mode Exit / PowerDown Mode Exit
Data Write / Output Enable

Calculate parameters

AS4C16M16SA chip parameters

Configuration for SystemClock=180Mhz and SDRAM clock rate 90Mhz. Some values are adjusted to work.

1 90 M h z = 11.1 u

All resulting values are rounded up.

Param in Datasheet Param Calc(cycles)
12u TMRD 1(1.1)+2 ???
tRC+tIS = 61.5u TXSR 6(5.5)+1 ???
42u TRAS 4(3.8)+1 ???
60u TRC 6(5.5)
12u TWR 2(1.1)
18u TRP 2(1.6)
18u TRCD 2(1.6)

This what worked for me, so should be right (maybe)

Configuration for SystemClock=180Mhz and SDRAM clock rate 60Mhz

1 60 M h z = 16.6 u
Param in Datasheet Param Calc(cycles)
12u TMRD 1(1.1)+2 ???
tRC+tIS = 61.5u TXSR 4(3.6)+1 ???
42u TRAS 3(2.5)
60u TRC 4(3.6)+1 ???
12u TWR 1(0.8)
18u TRP 1(1.1)
18u TRCD 1(1.1)

Calculate refresh rate

From datasheet - 8192 refresh cycles/64ms

64ms/8192 = 7.8u

7.8u * (90Mhz) = 702
7.8u * (60Mhz) = 402

Example config

Here is example config for AS4C16M16SA

  SDRAM->Init.SDBank             = FMC_SDRAM_BANK2;
  SDRAM->Init.ColumnBitsNumber   = FMC_SDRAM_COLUMN_BITS_NUM_9;
  SDRAM->Init.RowBitsNumber      = FMC_SDRAM_ROW_BITS_NUM_13;
  SDRAM->Init.MemoryDataWidth    = FMC_SDRAM_MEM_BUS_WIDTH_16;
  SDRAM->Init.InternalBankNumber = FMC_SDRAM_INTERN_BANKS_NUM_4;
  SDRAM->Init.CASLatency         = FMC_SDRAM_CAS_LATENCY_3;
  SDRAM->Init.WriteProtection    = FMC_SDRAM_WRITE_PROTECTION_DISABLE;
  SDRAM->Init.SDClockPeriod      = FMC_SDRAM_CLOCK_PERIOD_2; // 90Mhz
  SDRAM->Init.ReadBurst          = FMC_SDRAM_RBURST_DISABLE;
  SDRAM->Init.ReadPipeDelay      = FMC_SDRAM_RPIPE_DELAY_1;

  /* Timing configuration for 90 MHz of SDRAM clock frequency (180MHz/2) */
  SDRAM_Timing->LoadToActiveDelay    = 2;
  SDRAM_Timing->ExitSelfRefreshDelay = 7;
  SDRAM_Timing->SelfRefreshTime      = 4;      
  SDRAM_Timing->RowCycleDelay        = 7;//was 7
  SDRAM_Timing->WriteRecoveryTime    = 2;
  SDRAM_Timing->RPDelay              = 2;
  SDRAM_Timing->RCDDelay             = 2;

Using SDRAM

for (i = 0; i < SDRAM_SIZE; i++) {
    *(__IO uint16_t*) (SDRAM_BANK_ADDR + 2*i) = (uint16_t)0x00;
  }

Example of setting values into SDRAM. Accessing just like usual memory.

Links

  1. AS4C16M16SA datasheet
  2. STM32F429ZI description
  3. http://en.radzio.dxp.pl/stm32f429idiscovery/sdram.html