Send data from stm32f4 discovery to Raspberry Pi through spi

Question

The project is collecting Voltage & Current in 3.6Ksps, EMI in 2.4Msps by stm32f4 discovery and send them to Raspberry Pi. The first step is testing data transition from stm32f4 to RPI by spi. I define a unsigned data 111 in stm32f4, I am expecting it showing in RPI, but the print screen in RPI is showing 255 all the time.

Here is the code in stm32f4 as slave mode:

void SPI1_Init(void)
{    
  GPIO_InitTypeDef  GPIO_InitStructure;
  SPI_InitTypeDef  SPI_InitStructure;

  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);


  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3|GPIO_Pin_4|GPIO_Pin_5;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
  GPIO_Init(GPIOB, &GPIO_InitStructure);

    GPIO_PinAFConfig(GPIOB,GPIO_PinSource3,GPIO_AF_SPI1);
    GPIO_PinAFConfig(GPIOB,GPIO_PinSource4,GPIO_AF_SPI1);
    GPIO_PinAFConfig(GPIOB,GPIO_PinSource5,GPIO_AF_SPI1);


    RCC_APB2PeriphResetCmd(RCC_APB2Periph_SPI1,ENABLE);
    RCC_APB2PeriphResetCmd(RCC_APB2Periph_SPI1,DISABLE);

    SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
    SPI_InitStructure.SPI_Mode = SPI_Mode_Slave;
    SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
    SPI_InitStructure.SPI_CPOL = SPI_CPOL_High; 
    SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;    
    SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;   
    SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_2;  
    SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;  
    SPI_InitStructure.SPI_CRCPolynomial = 7;
    SPI_Cmd(SPI1, ENABLE);
    SPI1_ReadWriteByte(0xff);    
}   
SPI_BaudRate_Prescaler:SPI_BaudRatePrescaler_2~SPI_BaudRatePrescaler_256  

void SPI1_SetSpeed(u8 SPI_BaudRatePrescaler)
{
  assert_param(IS_SPI_BAUDRATE_PRESCALER(SPI_BaudRatePrescaler));
    SPI1->CR1&=0XFFC7;
    SPI1->CR1|=SPI_BaudRatePrescaler;
    SPI_Cmd(SPI1,ENABLE);
} 

u8 SPI1_ReadWriteByte(u8 TxData)
{                    

  while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE) == RESET){}

    SPI_I2S_SendData(SPI1, TxData);
  while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE) == RESET){}

    return SPI_I2S_ReceiveData(SPI1);
}

int main(void)
{ 
    u8 adcx=111;
    SPI1_Init();
    while(1)
    { 
        if(SPI1_ReadWriteByte(adcx))
        {
            SPI1_ReadWriteByte(adcx);               //send out data
        }
    }
}

Here is the code in RPI as Master mode in python:

import spidev
import time

spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 25000000
spi.lsbfirst = False
spi.mode = 0b11


while True:
    resp = spi.xfer([0x01])
    print(resp[0])
    time.sleep(1)

"But it seems like something wrong with the code." Is not even close to a specific problem description. Use a debugger to find the actualy problem. — too honest for this site
And use stdint.h types, not these 1990ies homebrew names like u8. C has evolved since these days. — too honest for this site
I am sorry for your confusion, the problem is that the screen in RPI shows 255 all the time, I am expecting 111 as it is defined in stm32f4. Thanks for your advice! — zb1872

Azrael Azrael · Accepted Answer · 2015-11-04T09:35:48

I'm pretty sure that your raspberry pi is too fast. Try a much slower SPI speed.

In my personal experience I have not been able to make the stm32f4 faster than 7 Mhz as SPI Slave and even that only with DMA.

If your application permits it, go to 100 kHz and it should work fine.

Send data from stm32f4 discovery to Raspberry Pi through spi

1 Answers