SPI

0. Pin Map

On the STM32F446RET6 Nucleo board, the SPI1 is connected as below

PA4	CS	A2
PA5	MOSI	PWM/MOSI/D11
PA6	MISO	MISO/D12
PA7	SCLK	SCK/D13

1. Configure STM32

First, set the configuration from the Template Project.

Set PA4 as GPIO Output.

In the left sidebar, select Connectivity -> SPI1.

Select Mode to "Full-Duplex Master".

Select Hardware NSS Signal to "Disable".

Set Clock Parameters -> Prescaler to 128 or more, to ensure the Baud Rate is slower than 1Mbits/s.

Errata: the hardware-driven NSS on STM32 is a bit mysterious. It seems that we need to deinit the SPI module and re-init to control the CS pin. Also, the CS pin is open-drain, so it requires an external pull-up resistor to function. We will save all the hassle and just use software-controlled CS pin. Detailed discussion of hardware NSS can be found here.

SPI Mode

Clock Polarity: CPOL

Clock Phase: CPHA

Mode	Clock Polarity	Clock Phase	Output Edge	Data Capture
MODE 0	Low	1 Edge	Falling	Rising
MODE 1	Low	2 Edge	Rising	Falling
MODE 2	High	1 Edge	Rising	Falling
MODE 3	High	2 Edge	Falling	Rising

2. Code

First, add the code from the Template Project.

In main.c, add the following code

  /* USER CODE BEGIN 2 */
  char str[64];
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET);
    uint8_t spi_tx_data[4];
    uint8_t spi_rx_data[4];
    spi_tx_data[0] = 0b10000000 | (0x36 << 1);
    spi_tx_data[1] = 0;
    spi_tx_data[2] = 0;
    spi_tx_data[3] = 0;
    HAL_SPI_TransmitReceive(&hspi1, spi_tx_data, spi_rx_data, 2, 100);
    while (hspi1.State == HAL_SPI_STATE_BUSY) {}
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);
    sprintf(str, "TX: %d %d %d %d\tRX: %d %d %d %d\r\n",
        spi_tx_data[0],
        spi_tx_data[1],
        spi_tx_data[2],
        spi_tx_data[3],
        spi_rx_data[0],
        spi_rx_data[1],
        spi_rx_data[2],
        spi_rx_data[3]
        );
    HAL_UART_Transmit(&huart2, (uint8_t *)str, strlen(str), 100);
    HAL_Delay(100);
  }
  /* USER CODE END 3 */

After saving, upload the code.

3. Result

After connecting an RFID-RC522 SPI module, we can see that we can read the register from the sensor. The SPI signal looks like this:

https://community.st.com/s/question/0D53W00001nAhvYSAS/how-to-use-spi-nss-on-stm32g0