STM32 SPI Slow Compute

Question

I\'m using a STM32F4 and its SPI to talk to a 74HC595 like in this tutorial. Difference is for starters I\'m using the non-DMA version for simplicity. I used STMCubeMX to co

Answer 1

So after some input I figured out a solution where I redefined the HAL functions and basically threw everything out that was slow:

void HAL_GPIO_WritePin_Fast(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin, GPIO_PinState PinState)
{

    if(PinState != GPIO_PIN_RESET)
    {
        GPIOx->BSRR = GPIO_Pin;
    }
    else
    {
        GPIOx->BSRR = (uint32_t)GPIO_Pin << 16U;
    }
}

HAL_StatusTypeDef HAL_SPI_Transmit_fast(SPI_HandleTypeDef *hspi, uint8_t *pData, uint16_t Size, uint32_t Timeout)
{
//    uint32_t tickstart = 0U;
    HAL_StatusTypeDef errorcode = HAL_OK;

    /* Check Direction parameter */

    /* Process Locked */
    __HAL_LOCK(hspi);

    /* Init tickstart for timeout management*/
//    tickstart = HAL_GetTick();

//    if(hspi->State != HAL_SPI_STATE_READY)
//    {
//        errorcode = HAL_BUSY;
//        goto error;
//    }
//
//    if((pData == NULL ) || (Size == 0))
//    {
//        errorcode = HAL_ERROR;
//        goto error;
//    }

    /* Set the transaction information */
    hspi->State       = HAL_SPI_STATE_BUSY_TX;
    hspi->ErrorCode   = HAL_SPI_ERROR_NONE;
    hspi->pTxBuffPtr  = (uint8_t *)pData;
    hspi->TxXferSize  = Size;
    hspi->TxXferCount = Size;

    /*Init field not used in handle to zero */
    hspi->pRxBuffPtr  = (uint8_t *)NULL;
    hspi->RxXferSize  = 0U;
    hspi->RxXferCount = 0U;
    hspi->TxISR       = NULL;
    hspi->RxISR       = NULL;

    /* Configure communication direction : 1Line */
    if(hspi->Init.Direction == SPI_DIRECTION_1LINE)
    {
        SPI_1LINE_TX(hspi);
    }

#if (USE_SPI_CRC != 0U)
    /* Reset CRC Calculation */
  if(hspi->Init.CRCCalculation == SPI_CRCCALCULATION_ENABLE)
  {
    SPI_RESET_CRC(hspi);
  }
#endif /* USE_SPI_CRC */

    /* Check if the SPI is already enabled */
    if((hspi->Instance->CR1 & SPI_CR1_SPE) != SPI_CR1_SPE)
    {
        /* Enable SPI peripheral */
        __HAL_SPI_ENABLE(hspi);
    }

    /* Transmit data in 16 Bit mode */
    if(hspi->Init.DataSize == SPI_DATASIZE_16BIT)
    {
        if((hspi->Init.Mode == SPI_MODE_SLAVE) || (hspi->TxXferCount == 0x01))
        {
            hspi->Instance->DR = *((uint16_t *)pData);
            pData += sizeof(uint16_t);
            hspi->TxXferCount--;
        }
        /* Transmit data in 16 Bit mode */
        while (hspi->TxXferCount > 0U)
        {
            /* Wait until TXE flag is set to send data */
            if(__HAL_SPI_GET_FLAG(hspi, SPI_FLAG_TXE))
            {
                hspi->Instance->DR = *((uint16_t *)pData);
                pData += sizeof(uint16_t);
                hspi->TxXferCount--;
            }
            else
            {
//                /* Timeout management */
//                if((Timeout == 0U) || ((Timeout != HAL_MAX_DELAY) && ((HAL_GetTick()-tickstart) >=  Timeout)))
//                {
//                    errorcode = HAL_TIMEOUT;
//                    goto error;
//                }
            }
        }
    }
        /* Transmit data in 8 Bit mode */
    else
    {
        if((hspi->Init.Mode == SPI_MODE_SLAVE)|| (hspi->TxXferCount == 0x01))
        {
            *((__IO uint8_t*)&hspi->Instance->DR) = (*pData);
            pData += sizeof(uint8_t);
            hspi->TxXferCount--;
        }
        while (hspi->TxXferCount > 0U)
        {
            /* Wait until TXE flag is set to send data */
            if(__HAL_SPI_GET_FLAG(hspi, SPI_FLAG_TXE))
            {
                *((__IO uint8_t*)&hspi->Instance->DR) = (*pData);
                pData += sizeof(uint8_t);
                hspi->TxXferCount--;
            }
            else
            {
//                /* Timeout management */
//                if((Timeout == 0U) || ((Timeout != HAL_MAX_DELAY) && ((HAL_GetTick()-tickstart) >=  Timeout)))
//                {
//                    errorcode = HAL_TIMEOUT;
//                    goto error;
//                }
            }
        }
    }





    /* Clear overrun flag in 2 Lines communication mode because received is not read */
    if(hspi->Init.Direction == SPI_DIRECTION_2LINES)
    {
        __HAL_SPI_CLEAR_OVRFLAG(hspi);
    }
#if (USE_SPI_CRC != 0U)
    /* Enable CRC Transmission */
  if(hspi->Init.CRCCalculation == SPI_CRCCALCULATION_ENABLE)
  {
     SET_BIT(hspi->Instance->CR1, SPI_CR1_CRCNEXT);
  }
#endif /* USE_SPI_CRC */

    if(hspi->ErrorCode != HAL_SPI_ERROR_NONE)
    {
        errorcode = HAL_ERROR;
    }

    error:
    hspi->State = HAL_SPI_STATE_READY;
    /* Process Unlocked */
    __HAL_UNLOCK(hspi);
    return errorcode;
}

That's definitely an option but probably not the most elegant :) It sped up the time dramatically though:

Edit: berendis solution is even faster:

Heres the code for multiple bytes:

spiTxBuf[0] = 0b00000110;
spiTxBuf[1] = 0b00000111;
spiTxBuf[2] = 0b00000111;
spiTxBuf[3] = 0b00000111;
spiTxBuf[4] = 0b00000111;

GPIOA->BSRR = 1 << (8 + 16);
for(int i=0; i<5; i++){
    *(volatile uint8_t *)&SPI1->DR = spiTxBuf[i];
    while ((SPI1->SR & SPI_SR_TXE) == RESET);

}

while((SPI1->SR & (SPI_SR_TXE | SPI_SR_BSY)) != SPI_SR_TXE);
GPIOA->BSRR = 1 << 8;
HAL_Delay(100);

Answer 2

How do i get that to toggle faster?

If possible, use the hardware NSS pin

Some STM32 controllers can toggle their NSS pin automatically, with a configurable delay after transmission. Check the Reference Manual, if yours is one of these, reconnect the latch pin of the shifter to the SPIx_NSS pin on the MCU.

Don't use HAL

HAL is quite slow and overcomplicated for anything with tight timing requirements. Don't use it.

Just implement the SPI transmit procedure in the Reference Manual.

SPI->CR1 |= SPI_CR1_SPE; // this is required only once
GPIOA->BSRR = 1 << (8 + 16);
*(volatile uint8_t *)&SPI->DR = 0b00000010;
while((SPI->SR & (SPI_SR_TXE | SPI_SR_BSY)) != SPI_SR_TXE)
    ;
GPIOA->BSRR = 1 << 8;