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SPI not providing output or clock, help please!

Question asked by kureigu on May 10, 2013
Latest reply on May 10, 2013 by kureigu
I've been struggling to get the SPI working on my STM32F3 Discovery, even just to communicate with the onboard rate sensor or work in loop-back mode. I got hold of a scope today, and realised that there's no output on my SPI1 SCLK/MOSI pins (PA5, PA7) and I have no idea why.
I've followed the set up guidelines in the peripheral manual, and as far as I can see SPI has been configured right. Unless I've forgotten to configure something else, I have no idea what's going on. Unfortunately the firmware available for the board has no SPI example either, as far as I can see.

My code is really simple too, I'm not even trying to use interrupts right now at all. At this point I'd even just like to see data on the MOSI pin.

I'd be really grateful if someone could check out my code and tell me if I've missed something.

/* Includes ------------------------------------------------------------------*/
#include "main.h"
/* variables ---------------------------------------------------------*/
GPIO_InitTypeDef        GPIO_InitStructure;
SPI_InitTypeDef         SPI_InitStructure;
/* function prototypes -----------------------------------------------*/
void delay_us(int us);
void SPI_GPIO_init(void);
void SPI_cfg(void);
uint8_t SPI1_read8bit(uint8_t addr);
int main(void)
        // read | addr of status register
    uint8_t test_data  = 0x80 | 0x0F;
    int rxbuf = 0;
  while (1){
        // Assert /CS followed by delay
        GPIO_ResetBits(GPIOE, GPIO_Pin_3); 
        // Send data byte
        rxbuf = SPI1_read8bit(test_data);
         // Deassert /CS after delay
        GPIO_SetBits(GPIOE, GPIO_Pin_3);
     delay_us(50); // wait 50us
// very roughly a 1us delay
void delay_us(int us){
    int i,k;
        for(i=0; i<8; i++);
/* Set up GPIO for SPI */
void SPI_GPIO_init(){
    //Disable SPI
    // Enable clock for SPI 1
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);   
    // Enable Clock for SPI GPIOA/E
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOE, ENABLE);
 // Configure GPIO Alternate function as SPI1
    GPIO_PinAFConfig(GPIOA, GPIO_Pin_5, GPIO_AF_5);  // SPI1 SCLK
    GPIO_PinAFConfig(GPIOA, GPIO_Pin_6, GPIO_AF_5);  // SPI1 MISO
    GPIO_PinAFConfig(GPIOA, GPIO_Pin_7, GPIO_AF_5);  // SPI1 MOSI  
    // Set up SCLK, MISO and MOSI pins
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;                                                  // Set as AF mode
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; 
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    // SCLK
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    // MISO
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    // MOSI
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    // Set up CS pin
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    // OType, Speed and PuPd are the same
    GPIO_Init(GPIOE, &GPIO_InitStructure);
    // Set CS high to begin
    GPIO_SetBits(GPIOE, GPIO_Pin_3);
/* Set up SPI and related parameters */
void SPI_cfg(){
    // Configure SPI
    SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
    SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
    SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_32;
    SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
    SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
    SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
    SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CRCPolynomial = 7;
  SPI_Init(SPI1, &SPI_InitStructure);
    /* Configure the RX FIFO Threshold */
  SPI_RxFIFOThresholdConfig(SPI1, SPI_RxFIFOThreshold_QF);
    // Enable SPI1
    SPI_Cmd(SPI1, ENABLE);
uint8_t SPI1_read8bit(uint8_t addr){
    while(SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE == 0) ); // Wait for TX buffer to be not empty. ie data loaded
    SPI_SendData8(SPI1, addr); // Send data
    while(SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE == 0) ); // Wait for TX buffer to be not empty. ie data loaded
    return SPI_ReceiveData8(SPI1); // Return received data