spi 应用层读值为0问题

news2024/10/6 8:25:43

昨天调SPI遇到读值为0x00，经排查是读写方向的问题。

#include <stdint.h>                                                             
#include <stdio.h>                                                              
#include <stdlib.h>   
#include <string.h>
#include <fcntl.h>      
#include <unistd.h>
#include <getopt.h>
#include <sys/ioctl.h>                                                          
#include <linux/spi/spidev.h>   
#include <linux/types.h>

#define D_SPI_READ_OP			( 1 << 7 )

static const char *device = "/dev/spidev0.0";
static int s_fd = -1; 
static uint8_t mode = SPI_MODE_0;
static uint8_t bits = 8;  
static uint32_t speed = 24000000;  

static void pabort(const char *s)
{
	perror(s);
	abort();
}

void spi_init_test()
{
    int ret = 0;         
  
    s_fd = open(device, O_RDWR);  
    if (s_fd < 0)  
        pabort("can't open device");  

    printf("open device sucucess %s\n", device);  
   /* 
    * spi mode 
     */  
    ret = ioctl(s_fd, SPI_IOC_WR_MODE, &mode);  
    if (ret == -1)  
        pabort("can't set spi mode");  
  
    ret = ioctl(s_fd, SPI_IOC_RD_MODE, &mode);  
    if (ret == -1)  
        pabort("can't get spi mode");  
  
    /* 
     * bits per word 
     */  
    ret = ioctl(s_fd, SPI_IOC_WR_BITS_PER_WORD, &bits);  
    if (ret == -1)  
        pabort("can't set bits per word");  
  
    ret = ioctl(s_fd, SPI_IOC_RD_BITS_PER_WORD, &bits);  
    if (ret == -1)  
        pabort("can't get bits per word");  
  
    /* 
     * max speed hz 
     */  
    ret = ioctl(s_fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);  
    if (ret == -1)  
        pabort("can't set max speed hz");  
  
    ret = ioctl(s_fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);  
    if (ret == -1)  
        pabort("can't get max speed hz");  
 
    printf("spi mode: %d\n", mode);  
    printf("bits per word: %d\n", bits);  
    printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);  
}

int SPI_Transfer(const uint8_t * tx_buf, uint8_t * rx_buf, int len)
{
	int ret;
	int i;

	struct spi_ioc_transfer tr ={
		.tx_buf = (unsigned long) tx_buf,
		.rx_buf = (unsigned long) rx_buf,
		.len =len,
		.delay_usecs = 0,
	};

	ret = ioctl(s_fd, SPI_IOC_MESSAGE(1), &tr);
	if (ret < 1)
		printf("can't send spi message");
	else
	{	
		printf("SPI Send [Len:%d]\n", len);
		printf("SPI Receive [len:%d]:", len);

		for (i = 0; i < len; i++)
		{
			printf("0x%02x ", rx_buf[i]);	// rx_buf[0]为0x00, rx_buf[1]是有效数据，还需找找原因。
		}
		printf("\n");
	}

	return ret;
}

int main()
{
	uint8_t r_buf[16] = {0};
	//uint8_t w_buf[12] = {0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a};
	uint8_t w_buf[1] = {0x75 | D_SPI_READ_OP};
	uint8_t ag_buf[1] = {0x1f | D_SPI_READ_OP};
	spi_init_test();
	while (1) {
		SPI_Transfer(w_buf, r_buf, 2);
		SPI_Transfer(ag_buf, r_buf, 12);
		usleep(1000*1000);
	}

	return 0;
}

/*
* SPI操作功能 (IMU ICM42686 手册上[9.6 SPI INTERFACE ]描述)
*/
   1.数据首先传递MSB，最后传递LSB
   2.数据在SCLK的上升沿被锁存
   3.数据应在SCLK的下降沿上转换
   4.SCLK的最大频率为24 MHz
   5.SPI读取和写入操作在16个或更多时钟周期(两个或更多字节)中完成。
       第一个字节包含SPI地址，后面的字节包含SPI数据。
       第一个字节的第一位包含读/写位，并指示读 (1) 或写 (0) 操作。
       以下7位包含寄存器地址。在多字节读/写的情况下，数据为两个或更多字节:

       SPI Address format
       MSB                   LSB
       R/W A6 A5 A4 A3 A2 A1 A0

       SPI Data format
       MSG                   LSB
       D7 D6 D5 D4 D3 D2 D1 D0

图：spi mode 3 波形图，寄存器0x75加上读标志1后为0xf5。