Trying to write 16 bits to a LCD via STM32H7 FMC memory controller end up in 4x16 bits write strobe [solved]

[Microman]

I'm trying to write to a single register of a LCD controller using the 16 Bit FMC peripheral in SRAM mode.

[update)

My assumption at the moment is that the controller writes 64 bits even the command STRH should only write a half word (16 bits).

When writing one single 16 bit word, the STM32H750VBT generates two #WR strobes within two #CS with alternating data in the second #CS sequence - for whatever reason I don't know. Reading from this address just works fine. One #RD, one #CS. I tried several options and timings, effect stays the same. CPU Cache is OFF. Has anyone an idea what I am doing wrong here? Thanks in advance!

I generated this init code with CubeMX:

SRAM_HandleTypeDef hsram1;
 
/* FMC initialization function */
void MX_FMC_Init(void)
{
  /* USER CODE BEGIN FMC_Init 0 */
 
  /* USER CODE END FMC_Init 0 */
 
  FMC_NORSRAM_TimingTypeDef Timing = {0};
 
  /* USER CODE BEGIN FMC_Init 1 */
 
  /* USER CODE END FMC_Init 1 */
 
  /** Perform the SRAM1 memory initialization sequence
  */
  hsram1.Instance = FMC_NORSRAM_DEVICE;
  hsram1.Extended = FMC_NORSRAM_EXTENDED_DEVICE;
  /* hsram1.Init */
  hsram1.Init.NSBank = FMC_NORSRAM_BANK1;
  hsram1.Init.DataAddressMux = FMC_DATA_ADDRESS_MUX_DISABLE;
  hsram1.Init.MemoryType = FMC_MEMORY_TYPE_SRAM;
  hsram1.Init.MemoryDataWidth = FMC_NORSRAM_MEM_BUS_WIDTH_16;
  hsram1.Init.BurstAccessMode = FMC_BURST_ACCESS_MODE_DISABLE;
  hsram1.Init.WaitSignalPolarity = FMC_WAIT_SIGNAL_POLARITY_LOW;
  hsram1.Init.WaitSignalActive = FMC_WAIT_TIMING_BEFORE_WS;
  hsram1.Init.WriteOperation = FMC_WRITE_OPERATION_ENABLE;
  hsram1.Init.WaitSignal = FMC_WAIT_SIGNAL_DISABLE;
  hsram1.Init.ExtendedMode = FMC_EXTENDED_MODE_DISABLE;
  hsram1.Init.AsynchronousWait = FMC_ASYNCHRONOUS_WAIT_DISABLE;
  hsram1.Init.WriteBurst = FMC_WRITE_BURST_DISABLE;
  hsram1.Init.ContinuousClock = FMC_CONTINUOUS_CLOCK_SYNC_ONLY;
  hsram1.Init.WriteFifo = FMC_WRITE_FIFO_DISABLE;
  hsram1.Init.PageSize = FMC_PAGE_SIZE_NONE;
  /* Timing */
  Timing.AddressSetupTime = 4;
  Timing.AddressHoldTime = 4;
  Timing.DataSetupTime = 1;
  Timing.BusTurnAroundDuration = 8;
  Timing.CLKDivision = 2;
  Timing.DataLatency = 5;
  Timing.AccessMode = FMC_ACCESS_MODE_A;
  /* ExtTiming */
 
  if (HAL_SRAM_Init(&hsram1, &Timing, NULL) != HAL_OK)
  {
    Error_Handler( );
  }
 
  /* USER CODE BEGIN FMC_Init 2 */
 
  /* USER CODE END FMC_Init 2 */
}

The test code that writes one half word to the base address

 for(;;) {

   *((uint16_t*)0x60000000) = (uint16_t)0x5555;

   HAL_Delay(100);

 }

This compiles into:

 
                 _writeReg:
  0x2401'3104: 0xb570         PUSH      {R4-R6, LR}
  0x2401'3106: 0x0004         MOVS      R4, R0
  0x2401'3108: 0x000d         MOVS      R5, R1
  0x2401'310a: 0x0016         MOVS      R6, R2
    *((uint16_t*)0x60000000) = (uint16_t)0x5555;
                 ??_writeReg_0:
  0x2401'310c: 0xf245 0x5055  MOVW      R0, #21845              ; 0x5555
  0x2401'3110: 0xf05f 0x41c0  MOVS.W    R1, #1610612736         ; 0x6000'0000
  0x2401'3114: 0x8008         STRH      R0, [R1]
    HAL_Delay(100);
  0x2401'3116: 0x2064         MOVS      R0, #100                ; 0x64
  0x2401'3118: 0xf7fc 0xfde2  BL        HAL_Delay               ; 0x2400'fce0
  0x2401'311c: 0xe7f6         B.N       ??_writeReg_0            ; 0x2401'310c

The signals look like this:

 is alternating with this

[Microman · Accepted solution]

For all who came to this topic because they have experienced the same issue, here is the fix:

"Remap FMC so that in MPU it is Device area"

https://community.st.com/s/question/0D53W00000HwJ8JSAV/stm32-fmc-sram-16bit-write-4-tims-a-call

Maybe ST could add a note in the next revision of the reference manual that users have to reconfigure the MPU to use 16 bit access to external memory devices.

[BEvan.2]

It seems the solution link gives me "access denied". Has this page been moved?