F7 QSPI issue

[_EFrie]

What kind of reason would the DR register read the same on subsequent calls in release build?

If I don't add __NOP()'s in there, the registers read the same and the FIFO doesn't get emptied.

Micro is STM32F769NI

static uint32_t drvInit(void) {
  uint32_t i = 0;
  struct {
    uint8_t manId;
    uint8_t memType;
    uint8_t memCapacity;
  } id;
  NVIC_SetPriority(DMA2_Stream2_IRQn, PRIORITY_QUADSPI_DMA);
  NVIC_EnableIRQ(DMA2_Stream2_IRQn);
  NVIC_SetPriority(QUADSPI_IRQn, PRIORITY_QUADSPI_INT);
  NVIC_EnableIRQ(QUADSPI_IRQn);
  //Reset QUADIO if is quad IO currently
  QUADSPI->CCR =
      QSPI_CCR_INSTR(SPI_FLASH_RST_QUAD) |
      QSPI_CCR_IMODE(QSPI_CCR_4LINES) |
      QSPI_CCR_FMODE_IW;
  while (QUADSPI->SR & QSPI_SR_BUSY_FLAG) {
  };
  QUADSPI->DLR = QSPI_DLR_COUNT(3);
  QUADSPI->CCR =
      QSPI_CCR_INSTR(SPI_FLASH_INS_RDID) |
      QSPI_CCR_IMODE(QSPI_CCR_1LINE) |
      QSPI_CCR_DCYC(0) |
      QSPI_CCR_DMODE(QSPI_CCR_1LINE) |
      QSPI_CCR_FMODE_IR;
  QUADSPI->AR = 0;
  while (!(QUADSPI->SR & QSPI_SR_TC_FLAG)) { //tc wait
  };
 
  id.manId = *(uint8_t *)&QUADSPI->DR;
  __NOP();//<-- Nop required for DR
  id.memType = *(uint8_t *)&QUADSPI->DR;
  __NOP();//<-- Nop required for DR
  id.memCapacity = *(uint8_t *)&QUADSPI->DR;
  //Set to 4 BYTE address
  QUADSPI->CCR =
      QSPI_CCR_INSTR(SPI_FLASH_INS_EN4BYTEADDR) |
      QSPI_CCR_IMODE(QSPI_CCR_1LINE) |
      QSPI_CCR_FMODE_IW;
  while (QUADSPI->SR & QSPI_SR_BUSY_FLAG) {
  };
 
  //Set to QUADIO
  QUADSPI->CCR =
      QSPI_CCR_INSTR(SPI_FLASH_ENT_QUAD) |
      QSPI_CCR_IMODE(QSPI_CCR_1LINE) |
      QSPI_CCR_FMODE_IW;
  while (QUADSPI->SR & QSPI_SR_BUSY_FLAG) {
  __NOP();
  };
 
  LL_DMA_EnableIT_TC(DMA2, LL_DMA_STREAM_2);
  LL_DMA_EnableIT_TE(DMA2, LL_DMA_STREAM_2);
  LL_DMA_SetChannelSelection(DMA2, LL_DMA_STREAM_2, LL_DMA_CHANNEL_11);
 
  return id.manId == JEDEC_MAN_ID &&
         id.memType == MICRON_3V_TYPE &&
         id.memCapacity == MICRON_512Mb;
}

[Tesla DeLorean]

id.manId = *(volatile uint8_t *)&QUADSPI->DR;

[_EFrie]

Hmm. volatile strikes again. I guess I need to start thinking compiler.

Thank you.

[Tesla DeLorean]

QUADSPI->DR has a volatile tag, but the explicit cast breaks that, the compiler is apt to fold