Upsilon/app/spi.c

#include <registers.h>
#include <FreeRTOS.h>
#include <task.h>
#include <timers.h>
#include <semphr.h>

/* This code sends data over SPI
 * We're using SPI4, in this pinout
 *
 * PE11 - SPI4_NSS - Yellow
 * PE12 - SPI4_SCK - Green
 * PE13 - SPI4_MISO - Red
 * PE14 - SPI4_MOSI - Blue
 */

void SpiSend(void * pvParameters) {
  uint16_t value = 0;
  while(1) {
    SPI_SR_t * spi_status = SPI_SR(SPI4);
    if (spi_status->BSY == 0) {
      uint16_t * SPI4_DR = (uint16_t *)(0x4001340C);
      *SPI4_DR = value++;
    }
    vTaskDelay(100/portTICK_PERIOD_MS);
  }
}

int main(int argc, char * argv[]) {
  // We'll use GPIO pins E11-E14 to emit SPI data
  // GPIO are grouped by letter, and GPIO "G" live on the "AHB1" bus (as all GPIOs BTW)
  // (this is documented in the STM32F4 reference mnual, page 65)

  // Step 1 : Enable clock in RCC_AHBxENR
  RCC_AHB1ENR->GPIOEEN = 1;

  // Step 2 : Configure the GPIO pin to "Alternate function number 5"
  // This means "SPI4 on pins E11-14", cf STM32F249 p78
  GPIO_MODER(GPIOE)->MODER11 = GPIO_MODE_ALTERNATE_FUNCTION;
  GPIO_MODER(GPIOE)->MODER12 = GPIO_MODE_ALTERNATE_FUNCTION;
  GPIO_MODER(GPIOE)->MODER13 = GPIO_MODE_ALTERNATE_FUNCTION;
  GPIO_MODER(GPIOE)->MODER14 = GPIO_MODE_ALTERNATE_FUNCTION;

  // We're interested in pins 11-14, which are in the 8-16 range, so we
  // have to deal with the "high" version of the AF register
  GPIO_AFRH(GPIOE)->AFRH11 = GPIO_AF_AF5;
  GPIO_AFRH(GPIOE)->AFRH12 = GPIO_AF_AF5;
  GPIO_AFRH(GPIOE)->AFRH13 = GPIO_AF_AF5;
  GPIO_AFRH(GPIOE)->AFRH14 = GPIO_AF_AF5;

  // Enable the SPI4 clock
  RCC_APB2ENR->SPI4EN = 1;

  // Configure the SPI port
  // Using a C99 compound litteral
  *SPI_CR1(SPI4) = (SPI_CR1_t){
    .BIDIMODE = 1,
    .BIDIOE = 1,
    .MSTR = 1,
    .DFF = SPI_DFF_16_BITS,
    .CPOL = 0,
    .BR = SPI_BR_DIV_256,
    .SSM = 1,
    .SSI = 1,
    .SPE = 1
  };

  BaseType_t success = xTaskCreate(SpiSend,
      "SpiSnd",
      100, // Stack size
      NULL, // Parameters
      2,
      NULL);

  vTaskStartScheduler();

  while (1) {
    // We should never get here
  }
}