STM32G071 ILI9341 SPI DMA Problem

[Lennyn22]

I am working on a project that requires a 320x240 LCD panel (ILI9341).  I use a nucleo board with STM32G071RB chip. The SPI communication works fine when I use a blocking HAL_SPI_Transmit() function, but it takes a while to fill the entire screen. When I use a DMA with SPI to speed it up, all colors get distorted. 

I have tried a HAL_SPI_Transmit_DMA()  - transmit only function, and a two way HAL_SPI_TransmitReceive_DMA() function.  I tried switching from 8-bit SPI to 16-bit SPI mode for DMA transfer, but always get the same color distortion problem.

A detailed analysis revealed the core problem. While transmitting the RGB565 pixel information 'RRRRRGGGGGGBBBBB', the 16-bit data is broken into two bytes 'RRRRRGGG' and 'GGGBBBBB'. In the blocking SPI transmit function both bytes are transferred.  With any configuration SPI -DMA, the second bit gets lost.  The ILI9341 controller receives a single byte and for some reason reads it, according to ChatGPT, as RGB332 'RRRBBGGG' .  There is obvious mismatch even with the RGB332 coding, that Chat GPT failed to clearly interpret.  However, it was confirmed with numerous bit-by-bit manipulations.

I will post here just one configuration of the numerous I tried.

Here is the SPI and DMA setup. 

  /* SPI1 parameter configuration*/
 __HAL_RCC_SPI1_CLK_ENABLE();

  hspi1.Instance = SPI1;
  hspi1.Init.Mode = SPI_MODE_MASTER;
  hspi1.Init.Direction = SPI_DIRECTION_1LINE;
  hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
  hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
  hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
  hspi1.Init.NSS = SPI_NSS_SOFT;
  hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_16;
  hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi1.Init.CRCPolynomial = 7;
  hspi1.Init.CRCLength = SPI_CRC_LENGTH_DATASIZE;
  hspi1.Init.NSSPMode = SPI_NSS_PULSE_ENABLE;

  static void MX_DMA_Init(void)
  {

    /* DMA controller clock enable */
    __HAL_RCC_DMA1_CLK_ENABLE();

    hdma_spi1_tx.Instance = DMA1_Channel3;
    hdma_spi1_tx.Init.Request = DMA_REQUEST_SPI1_TX;
    hdma_spi1_tx.Init.Direction = DMA_MEMORY_TO_PERIPH;
    hdma_spi1_tx.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_spi1_tx.Init.MemInc = DMA_MINC_ENABLE;   
    hdma_spi1_tx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
    hdma_spi1_tx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
    hdma_spi1_tx.Init.Mode = DMA_NORMAL;
    hdma_spi1_tx.Init.Priority = DMA_PRIORITY_HIGH;

    HAL_DMA_Init(&hdma_spi1_tx);
    __HAL_LINKDMA(&hspi1, hdmatx, hdma_spi1_tx);

    /* DMA interrupt init */
    /* DMA1_Channel2_3_IRQn interrupt configuration */
    HAL_NVIC_SetPriority(DMA1_Channel2_3_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(DMA1_Channel2_3_IRQn);

The Fill Screen function looks like this:

// Fill entire screen with ONE variable

static uint8_t blockbuf[TFT_WIDTH * BLOCK_LINES * 2];

volatile uint8_t spi_dma_done = 0;

void ILI9341_FillScreen_Color(uint16_t color)
{
    uint16_t y = 0;

    uint8_t hi = color >> 8;
    uint8_t lo = color & 0xFF;

    /* Prepare one full block */
    for (uint32_t i = 0; i < TFT_WIDTH * BLOCK_LINES; i++)
    {
        blockbuf[2*i]     = hi;
        blockbuf[2*i + 1] = lo;
    }

    while (y < TFT_HEIGHT)
    {
        uint16_t lines = BLOCK_LINES;
        if (y + lines > TFT_HEIGHT)
            lines = TFT_HEIGHT - y;

        uint32_t bytes = TFT_WIDTH * lines * 2;

        /* --- Address window (command phase) --- */
        CS_LOW();
        ILI9341_SetAddressWindow_NoCS(
            0,
            y,
            TFT_WIDTH - 1,
            y + lines - 1
        );

        /* --- Data phase --- */
        DC_DATA();

        /* Start DMA */
        HAL_SPI_Transmit_DMA(&hspi1, blockbuf, bytes);

        /* Wait for completion */
        while (HAL_SPI_GetState(&hspi1) != HAL_SPI_STATE_READY);
        while (SPI1->SR & SPI_SR_BSY);

     //   CS_HIGH(); // CS is turned off in the callback function.

        y += lines;
    }
}


void HAL_SPI_TxRxCpltCallback(SPI_HandleTypeDef *hspi)
{
    if (hspi == &hspi1)
    {
        CS_HIGH();
        spi_dma_done = 1;
    }
}

At this moment I (and Chat GPT) have exhausted our options. Any suggestion would be greatly appreciated.

[mƎALLEm]

Hello,

You need to probe what is going on on the SPI line (MOSI) versus what it should be seen.