Linux用户态如何使用spi？

在用户态访问spi从设备也是比较常用的功能。下面的例子就实现了如何读取和设置spi从设备的GPIO引脚？

实验环境

raspberry pi3b

Linux raspberrypi 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr  3 17:24:16 BST 2023 aarch64 GNU/Linux

测试代码

// simple.c

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

static const uint8_t mode = 0;
static const uint32_t speed = 500000;
static const uint8_t bits = 0;

static int _spi_transfer(int fd, uint8_t *data, int len) {
    struct spi_ioc_transfer spi[len];

    for (int i = 0; i < len; i++) {
        memset(&spi[i], 0, sizeof(struct spi_ioc_transfer));
        spi[i].tx_buf = (unsigned long)(data + i);
        spi[i].rx_buf = (unsigned long)(data + i);
        spi[i].len = 1;
        spi[i].speed_hz = speed;
        spi[i].bits_per_word = bits;
    }

    if (ioctl(fd, SPI_IOC_MESSAGE(len), spi) < 0) {
        perror("ioctl SPI_IOC_MESSAGE");
        return -1;
    }

    return 0;
}

int main(int argc, char *argv[]) {
    // cmd|address|data
    // cmd => 0 1 0 0 0 A1 A2 R/W
    // A1 A2为SPI设备片选地址
    unsigned char data[3];

    int fd = open("/dev/spidev0.0", O_RDWR);
    if (fd < 0) {
        perror("open /dev/spidev0.0");
        return -1;
    }

    if (ioctl(fd, SPI_IOC_WR_MODE, &mode) < 0) {
        perror("ioctl SPI_IOC_WR_MODE");
        close(fd);
        return -1;
    }

    if (ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed) < 0) {
        perror("ioctl SPI_IOC_WR_MAX_SPEED_HZ");
        close(fd);
        return -1;
    }

    if (ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits) < 0) {
        perror("ioctl SPI_IOC_WR_BITS_PER_WORD");
        close(fd);
        return -1;
    }

    // 设置GPIO 1引脚方向
    data[0] = 0x40, data[1] = 0x00, data[2] = 0xfe;
    if (_spi_transfer(fd, data, 3)) {
        perror("set GPIO direction");
        close(fd);
        return -1;
    }

    // 设置GPIO 1电平
    data[0] = 0x40, data[1] = 0x0a;
    data[2] = argc > 1 ? atoi(argv[1]) > 0 : 0x00;
    if (_spi_transfer(fd, data, 3)) {
        perror("set GPIO");
        close(fd);
        return -1;
    }

    // 读取Button数据
    data[0] = 0x41, data[1] = 0x09, data[2] = 0x00;
    if (_spi_transfer(fd, data, 3)) {
        perror("read button state");
        close(fd);
        return -1;
    }

    printf("button is %s\n",
           ((data[2] & (1 << 1)) > 0) ? "pressed" : "not pressed");

    close(fd);
    return 0;
}

编译脚本

#!/bin/sh

all: simple.c
        gcc -g -o simple simple.c

clean:
        -rm simple

测试

• 编译程序：make

• 点亮LED：sudo ./simple 1

• 关闭LED：sudo ./simple 0