spi_helper.c

static inline uint8_t spi_send(SPI_TypeDef* SPI, uint8_t data) {
    SPI->DR = data;

    while (!(SPI->SR & SPI_FLAG_TXE));

    while (!(SPI->SR & SPI_FLAG_RXNE));

    return SPI->DR;
}

// responses to cmd_buffer are ignored, responses to data_buffer are stored in data_buffer
void spi_tx(const spi_cfg_t cfg, const uint8_t *cmd_buffer, int cmd_buffer_len, uint8_t *data_buffer, int data_buffer_len, uint8_t flags) {
  // just to be safe
  master_int_disable();
  
  // CS low
  ((GPIO_TypeDef *) cfg.port_cs)->ODR &= !cfg.pin_cs;

  for (int i = 0; i < cmd_buffer_len; ++i) {
    spi_send((SPI_TypeDef*) cfg.base, cmd_buffer[i]);
  }

  uint8_t data;
  for (int i = 0; i < data_buffer_len; ++i) {
    data = spi_send((SPI_TypeDef*) cfg.base, data_buffer[i]);

    if (!(flags & SPI_DATA_IMMUTABLE))
      data_buffer[i] = data;
  }

  while (((SPI_TypeDef*) cfg.base)->SR & SPI_FLAG_BSY);

  // CS high
  ((GPIO_TypeDef *) cfg.port_cs)->ODR |= cfg.pin_cs;
  
  master_int_enable();
}