linux SPI bus demo hacking

/**********************************************************************
 *                    linux SPI bus demo hacking
 * 说明：
 *     本文主要解析linux应用程序如何使用SPI总线和设备通信。
 *
 *                                    2016-3-28 深圳 南山平山村 曾剑锋
 *********************************************************************/

// 参考文档：
//     1. getopt_long
//         http://baike.baidu.com/link?url=6KJogehaQx-6OWyU0882g2P5Fdp-NoKBPJOBGYbx-gQIT6km2myaonw2nOheKsSoMXtDQTqsuVmTwS7trQ5vxq
//     2. Linux Signal (10): abort函数
//         http://blog.csdn.net/yylklshmyt20090217/article/details/4234237
//     3. 用户空间的spi驱动
//         http://blog.csdn.net/liangxiaozhang/article/details/7601880

/*
 * SPI testing utility (using spidev driver)
 *
 * Copyright (c) 2007  MontaVista Software, Inc.
 * Copyright (c) 2007  Anton Vorontsov <avorontsov@ru.mvista.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License.
 *
 * Cross-compile with cross-gcc -I/path/to/cross-kernel/include
 */

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

// 计算数组大小宏
#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))

static void pabort(const char *s)
{
    perror(s);
    // 终止程序运行
    abort();
}

// 默认spi设备节点
static const char *device = "/dev/spidev1.0";
static uint8_t mode;
static uint8_t bits = 8;
static uint32_t speed = 500000;
static uint16_t delay;

static void transfer(int fd)
{
    int ret;
    // 要发送的数据
    uint8_t tx[] = {
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        0xDE, 0xAD, 0xBE, 0xEF, 0xBA, 0xAD,
        0xF0, 0x0D,
    };
    // 接收的数据，接收的数据长度和发送的数据长度是一样的，初始化为0。
    uint8_t rx[ARRAY_SIZE(tx)] = {0, };
    // 发送数据结构体
    struct spi_ioc_transfer tr = {
        .tx_buf = (unsigned long)tx,    // 写数据缓冲
        .rx_buf = (unsigned long)rx,    // 读数据缓冲
        .len = ARRAY_SIZE(tx),          // 缓冲的长度
        .delay_usecs = delay,           // 两个spi_ioc_transfer之间的延时
        .speed_hz = speed,              // 通信的时钟频率
        .bits_per_word = bits,          // 字长（比特数）
    };

    // 发送数据
    ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
    if (ret < 1)
        pabort("can't send spi message");

    // 显示输出发送buf的数据内容
    for (ret = 0; ret < ARRAY_SIZE(tx); ret++) {
        if (!(ret % 6))
            puts("");
        printf("%.2X ", rx[ret]);
    }
    puts("");
}

// 输出显示使用方法
static void print_usage(const char *prog)
{
    printf("Usage: %s [-DsbdlHOLC3]\n", prog);
    puts("  -D --device   device to use (default /dev/spidev1.1)\n"
         "  -s --speed    max speed (Hz)\n"
         "  -d --delay    delay (usec)\n"
         "  -b --bpw      bits per word \n"
         "  -l --loop     loopback\n"
         "  -H --cpha     clock phase\n"
         "  -O --cpol     clock polarity\n"
         "  -L --lsb      least significant bit first\n"
         "  -C --cs-high  chip select active high\n"
         "  -3 --3wire    SI/SO signals shared\n");
    exit(1);
}

static void parse_opts(int argc, char *argv[])
{
    while (1) {

        /**
         * struct option {
         *     const char *name;
         *     int         has_arg;
         *     int        *flag;
         *     int         val;
         * };
         * The meanings of the different fields are:
         *     name   is the name of the long option.
         *
         *     has_arg
         *         is: no_argument (or 0) if the option does not take an
         *         argument; required_argument (or 1) if the option requires an
         *         argument; or optional_argument (or 2) if the option takes an
         *         optional argument.
         *
         *     flag specifies how results are returned for a long option.  If flag
         *         is NULL, then getopt_long() returns val.  (For example, the
         *         calling program may set val to the equivalent short option
         *         character.)  Otherwise, getopt_long() returns 0, and flag
         *         points to a variable which is set to val if the option is
         *         found, but left unchanged if the option is not found.
         *
         *     val  is the value to return, or to load into the variable pointed
         *         to by flag.
         *
         */
        static const struct option lopts[] = {
            { "device",  1, 0, 'D' },
            { "speed",   1, 0, 's' },
            { "delay",   1, 0, 'd' },
            { "bpw",     1, 0, 'b' },
            { "loop",    0, 0, 'l' },
            { "cpha",    0, 0, 'H' },
            { "cpol",    0, 0, 'O' },
            { "lsb",     0, 0, 'L' },
            { "cs-high", 0, 0, 'C' },
            { "3wire",   0, 0, '3' },
            { "no-cs",   0, 0, 'N' },
            { "ready",   0, 0, 'R' },
            { NULL, 0, 0, 0 },
        };
        int c;

        /**
         * 1. 函数中的argc和argv通常直接从main()的两个参数传递而来。
         * 2. 字符串optstring可以下列元素:
         *     1.单个字符，表示选项，
         *     2.单个字符后接一个冒号：表示该选项后必须跟一个参数。参数紧跟在选项后或者以空格隔开。该参数的指针赋给optarg。
         *     3 单个字符后跟两个冒号，表示该选项后可以有参数也可以没有参数。如果有参数，参数必须紧跟在选项后不能以空格隔开。该参数的指针赋给optarg。（这个特性是GNU的扩张）。
         * 3. 参数longopts，其实是一个结构的实例。
         * 4. 参数longindex，表示当前长参数在longopts中的索引值。
         * 5. 给个例子：
         *     struct option long_options[] = {
         *         {"a123", required_argument, 0, 'a'},
         *         {"c123", no_argument, 0, 'c'},
         *     }
         *     现在，如果命令行的参数是-a 123，那么调用getopt_long()将返回字符'a',并且将字符串123由optarg返回(注意注意！字符串123由optarg带回！optarg不需要定义，在getopt.h中已经有定义)，那么，如果命令行参数是-c，那么调用getopt_long()将返回字符'c',而此时，optarg是null。最后，当getopt_long()将命令行所有参数全部解析完成后，返回-1。
         */
        c = getopt_long(argc, argv, "D:s:d:b:lHOLC3NR", lopts, NULL);

        // 这里表示解析参数已经到了最后一个，会跳出while循环
        if (c == -1)
            break;

        switch (c) {
        case 'D':
            device = optarg;            // getopt_long函数将参数指针放在optarg中
            break;
        case 's':
            speed = atoi(optarg);       // 将optarg字符串转成int型数字
            break;
        case 'd':
            delay = atoi(optarg);
            break;
        case 'b':
            bits = atoi(optarg);
            break;
        case 'l':
            mode |= SPI_LOOP;
            break;
        case 'H':
            mode |= SPI_CPHA;
            break;
        case 'O':
            mode |= SPI_CPOL;
            break;
        case 'L':
            mode |= SPI_LSB_FIRST;
            break;
        case 'C':
            mode |= SPI_CS_HIGH;
            break;
        case '3':
            mode |= SPI_3WIRE;
            break;
        case 'N':
            mode |= SPI_NO_CS;
            break;
        case 'R':
            mode |= SPI_READY;
            break;
        default:
            print_usage(argv[0]);
            break;
        }
    }
}

int main(int argc, char *argv[])
{
    int ret = 0;
    int fd;

    // 参数解析
    parse_opts(argc, argv);

    // 打开设备
    fd = open(device, O_RDWR);
    if (fd < 0)
        pabort("can't open device");

    /*
     * spi mode
     * 设置spi模式
     */
    ret = ioctl(fd, SPI_IOC_WR_MODE, &mode);
    if (ret == -1)
        pabort("can't set spi mode");

    // 读取spi模式
    ret = ioctl(fd, SPI_IOC_RD_MODE, &mode);
    if (ret == -1)
        pabort("can't get spi mode");

    /*
     * bits per word
     * 设置spi字节位数
     */
    ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
    if (ret == -1)
        pabort("can't set bits per word");

    // 读取spi字节位数
    ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
    if (ret == -1)
        pabort("can't get bits per word");

    /*
     * max speed hz
     * 设置spi最大速率
     */
    ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
    if (ret == -1)
        pabort("can't set max speed hz");

    // 设置spi最大速率
    ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
    if (ret == -1)
        pabort("can't get max speed hz");

    // 显示设置的spi相关参数，这里输出的都是设置了之后，又重新读回来的值，
    // 便于确认你设置的值和真是程序运行的值是否有差异。
    printf("spi mode: %d\n", mode);
    printf("bits per word: %d\n", bits);
    printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);

    // 发送数据
    transfer(fd);

    // 关闭设备节点
    close(fd);

    return ret;
}