Where are defined AF numbers for pins?

Pavel A. · ‎2021-06-26

I have a project for H743 with three SPIs.

CubeMX creates the following code for initializing SPI pins:

void HAL_SPI_MspInit(SPI_HandleTypeDef* hspi)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};
  if(hspi->Instance==SPI1)
  {
    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI1;
    PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
    {
      Error_Handler();
    }
 
    __HAL_RCC_SPI1_CLK_ENABLE();
 
    __HAL_RCC_GPIOA_CLK_ENABLE();
    __HAL_RCC_GPIOB_CLK_ENABLE();
    /**SPI1 GPIO Configuration
    PA5     ------> SPI1_SCK
    PA6     ------> SPI1_MISO
    PB5     ------> SPI1_MOSI
    */
    GPIO_InitStruct.Pin = GPIO_PIN_5|GPIO_PIN_6;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
    GPIO_InitStruct.Pin = GPIO_PIN_5;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
  }
  else if(hspi->Instance==SPI2)
  {
    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI2;
    PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
    {
      Error_Handler();
    }
 
    __HAL_RCC_SPI2_CLK_ENABLE();
 
    __HAL_RCC_GPIOC_CLK_ENABLE();
    __HAL_RCC_GPIOB_CLK_ENABLE();
    /**SPI2 GPIO Configuration
    PC2_C     ------> SPI2_MISO
    PC3_C     ------> SPI2_MOSI
    PB10     ------> SPI2_SCK
    */
    GPIO_InitStruct.Pin = GPIO_PIN_2|GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF5_SPI2;
    HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);
 
    GPIO_InitStruct.Pin = GPIO_PIN_10;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF5_SPI2;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
  }
  else if(hspi->Instance==SPI3)
  {
    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI3;
    PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
    {
      Error_Handler();
    }
 
    __HAL_RCC_SPI3_CLK_ENABLE();
 
    __HAL_RCC_GPIOB_CLK_ENABLE();
    __HAL_RCC_GPIOC_CLK_ENABLE();
    /**SPI3 GPIO Configuration
    PB2     ------> SPI3_MOSI
    PC10     ------> SPI3_SCK
    PC11     ------> SPI3_MISO
    */
    GPIO_InitStruct.Pin = GPIO_PIN_2;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF7_SPI3;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
 
    GPIO_InitStruct.Pin = GPIO_PIN_10|GPIO_PIN_11;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF6_SPI3;
    HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);
  }
}

Notice that for SPI2 all pins have AF=5, but for SPI3 some pins have AF=6 and some AF=7.

How one can discover these values, besides of reading Cube generated code (or templates)?

These AFs are defined in stm32h7xx_hal_gpio_ex.h.

For AF=5 there are definitions for SPI1 to 6.

For AF=6 there are definitions for SPI2 and 3.

For AF=7 there are definitions for SPI2,3,6 .

So, how one should guess which value to use for SPI2 and 3?

I could not find this info in DS12117, neither in RM0433.