STM32: simple SPI transfer

Question

I am working with a STM32F3DISCOVERY board and I'm trying to dive a bit deeper into the abstractions of the HAL. I made a simple version of a function that transmits data over SPI, sadly it does not work (at least the DAC I'm sending it to does not change state) and I'm not sure what I am missing there. Maybe there's also something in the initialization code that doesn't work with my simple version. I'd be happy for any guidance or references I could check. Thank you!

#include <stm32f3xx_hal.h>

#define PINS_SPI GPIO_PIN_5 | GPIO_PIN_7
#define GPIO_PORT GPIOA

/* This is the simplest function I could come up with to do the transfer but I'm clearly missing something here */
uint8_t SPI_SendReceive(SPI_HandleTypeDef *hspi, uint8_t data) {
  /* Loop while DR register in not empty */
  while ((hspi->Instance->SR & SPI_FLAG_TXE) == RESET) {
  }

  /* Send data through the SPI1 peripheral */
  hspi->Instance->DR = data;

  /* Wait to receive data */
  while ((hspi->Instance->SR & SPI_FLAG_RXNE) == RESET) {
  }

  return hspi->Instance->DR;
}

int main() {
  HAL_Init();


  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_SPI1_CLK_ENABLE();

  static SPI_HandleTypeDef spi = {.Instance = SPI1};
  spi.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;
  spi.Init.Direction = SPI_DIRECTION_2LINES;
  spi.Init.CLKPhase = SPI_PHASE_1EDGE;
  spi.Init.CLKPolarity = SPI_POLARITY_LOW;
  spi.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  spi.Init.DataSize = SPI_DATASIZE_8BIT;
  spi.Init.FirstBit = SPI_FIRSTBIT_MSB;
  spi.Init.NSS = SPI_NSS_HARD_OUTPUT;
  spi.Init.TIMode = SPI_TIMODE_DISABLE;
  spi.Init.Mode = SPI_MODE_MASTER;

  HAL_SPI_Init(&spi);
  __HAL_SPI_ENABLE(&spi);

  GPIO_InitTypeDef GPIO_InitStruct;
  GPIO_InitStruct.Pin = PINS_SPI;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;

  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  GPIO_InitStruct.Pin = GPIO_PIN_4;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;

  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
  
  /* TI 8564 DAC Settings */
  uint8_t cmd1 = 0b00010000;
  /* DAC output value (16-bit) */
  uint16_t cmd23 = 0;
  uint8_t cmd2 = cmd23 >> 8;
  uint8_t cmd3 = cmd23 & 0xff;

  uint8_t command[3] = {cmd1, cmd2, cmd3};

  while (true) {
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET);

    /* This does not work :( */
    SPI_SendReceive(&spi, command[0]);
    SPI_SendReceive(&spi, command[1]);
    SPI_SendReceive(&spi, command[2]);
    
    /* This works! When commenting in the lines above and commenting this out */
    /* HAL_SPI_Transmit(&spi, command, 3, HAL_MAX_DELAY); */

    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);

    HAL_Delay(1000);
  }
}

Answer 1

Check the contents of HAL_SPI_Init. Most likely this function calls another function which is supposed to do the low-level initialization, and you're responsible to provide this function yourself. To make it more complex, this alleged second function already has a "dummy" weak alias defined, so the toolchain doesn't return any error but just builds a code unable to do anything.