Correct way to deactivate SPI in half-duplex/simplex mode STM32F4

Question

I am trying to change a STM32F4 from slave to master after certain amount of time, send a message as master, and go back to slave. I found out that configuring the SPI as slave_rxonly and enabling the SPI will cause the clock to unexpectedly sent a clock as soon as I configure the device back to master. Without me sending any data. I assume its becasue I am either initializing the peripheral wrong or deinitializing it incorrectly

This is my main loop.

  while (1)
  {
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
      MX_SPI1_Init(); /* This configures master */
      HAL_Delay(10);
 
      sendHelloWorld();
      configSlave(); /* Configures slave mode */
      __HAL_SPI_ENABLE(&hspi1); /* Enabling the device in this mode generates a continous clock during master init */
 
      HAL_Delay(100);
 
      HAL_SPI_DeInit(&hspi1);   /* Disables SPI and de-initializes the peripheral */
  }

My master config:

  hspi1.Instance = SPI1;
  hspi1.Init.Mode = SPI_MODE_MASTER;
  hspi1.Init.Direction = SPI_DIRECTION_2LINES;
  hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
  hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
  hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
  hspi1.Init.NSS = SPI_NSS_SOFT;
  hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;
  hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi1.Init.CRCPolynomial = 10;
  if (HAL_SPI_Init(&hspi1) != HAL_OK)
  {
    Error_Handler();
  }

My slave config:

if(HAL_SPI_DeInit(&hspi1) != HAL_ERROR)
{
       /* SPI1 parameter configuration*/
    hspi1.Instance = SPI1;
    hspi1.Init.Mode = SPI_MODE_SLAVE;
    hspi1.Init.Direction = SPI_DIRECTION_2LINES_RXONLY;
    hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
    hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
    hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
    hspi1.Init.NSS = SPI_NSS_SOFT;
    hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
    hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
    hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
    hspi1.Init.CRCPolynomial = 10;
 
    if (HAL_SPI_Init(&hspi1) != HAL_OK)
    {
        Error_Handler();
    }
 
}

and this is the waveform from my logic analyzer. As soon as I run the function MX_SPI1_Init() after enabling the SPI as a Slave the clock is generated. Orange is the clock and as you can see - from the 10ms delay -it gets enabled right after the initialization as master.

Any thoughts? I've been fighting with this issue for over a week, and tried many things

score 3 · Accepted Answer · answered Apr 23 '21 at 06:57

3

Possibly the rubbish HAL function accidentally changes temporarily to master rx-only. Various HAL functions are naive in the order they write to registers and create glitches like this. Try calling HAL_SPI_DeInit before reconfiguring. Alternatively just ditch the HAL altogether.

Master RX-only always has to blindly output the clock. If you want to control when the clock is sent then use master tx and rx mode, and then write the same amount of dummy data that you want to read. If you want MOSI to remain tristate and not send the dummy data then you could change the pin to GPIO mode while you do this.

answered Apr 23 '21 at 06:57

Tom V

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Yes. HAL has been a pain, and I will most likely have to create my own implementation, however, I though it was going to be easier to experiment with the HAL beforehand. Somebody on ST community told me to never disable the SPI (SPE reg), and just change the master/slave config. That solved it, but I don't think that should be the correct way. – Farynx Apr 23 '21 at 13:43
If this fixed your problem can you please accept the answer with the green tick mark on the left? thanks. – Tom V Apr 29 '21 at 11:18

Correct way to deactivate SPI in half-duplex/simplex mode STM32F4

1 Answers1