Continuous DMA from memory to SPI

[SoCalJim]

We need to continuously DMA a single 16-bit word to the SPI transmitter. (Neither the memory address nor the peripheral address would increment.) Can this be done without intervention? I.e. do we have to use a DMA Complete interrupt to set a flag and call HAL_SPI_Transmit_DMA whenever the flag gets set, or can we configure HAL_SPI_Transmit_DMA to set and forget it?

[SoCalJim]

Here's the relevant code:

MX_SPI2_Init

  hspi2.Instance = SPI2;

  hspi2.Init.Mode = SPI_MODE_MASTER;

  hspi2.Init.Direction = SPI_DIRECTION_2LINES;

  hspi2.Init.DataSize = SPI_DATASIZE_16BIT;

  hspi2.Init.CLKPolarity = SPI_POLARITY_HIGH;

  hspi2.Init.CLKPhase = SPI_PHASE_2EDGE;

  hspi2.Init.NSS = SPI_NSS_HARD_OUTPUT;

  hspi2.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_2;

  hspi2.Init.FirstBit = SPI_FIRSTBIT_MSB;

  hspi2.Init.TIMode = SPI_TIMODE_DISABLE;

  hspi2.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;

  hspi2.Init.CRCPolynomial = 7;

  hspi2.Init.CRCLength = SPI_CRC_LENGTH_DATASIZE;

  hspi2.Init.NSSPMode = SPI_NSS_PULSE_ENABLE;

HAL_SPI_MspInit

    /**SPI2 GPIO Configuration

    PC1     ------> SPI2_MOSI

    PB10     ------> SPI2_SCK

    PB12     ------> SPI2_NSS

    */

    GPIO_InitStruct.Pin = SPI2_MOSI;

    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;

    GPIO_InitStruct.Pull = GPIO_NOPULL;

    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;

    GPIO_InitStruct.Alternate = GPIO_AF3_SPI2;

    HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);

    // Remove SPI2_NSS_Pin

    GPIO_InitStruct.Pin = SPI2_CLK|SPI2_NSS;

    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;

    GPIO_InitStruct.Pull = GPIO_NOPULL;

    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;

    GPIO_InitStruct.Alternate = GPIO_AF5_SPI2;

    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

Main

    HAL_StatusTypeDef status = HAL_SPI_Transmit_IT(&hspi2, (uint8_t *)&buf, 1);

[SoCalJim]

As a sanity check, I set SPI2_NSS_Pin's mode to GPIO_MODE_OUTPUT_PP. In doing so I found I had to reduce the voltage scale. You can see that the SPI2_NSS is wired properly.

[TDK]

>   hspi2.Init.CLKPhase = SPI_PHASE_2EDGE;

NSSP only works with CPHA=0, so change this to SPI_PHASE_1EDGE.

[SoCalJim]

That worked! :) :) Thanks!

Now is there a way to invert that line, or do we have to do that in hardware?

[TDK]

What line do you want to invert? Probably needs to be done in hardware.

[SoCalJim]

NSS

[TDK]

I don't think the STM32L4 can change the polarity of NSS internally.

The STM32H7 series (and probably other newer chips) can: