Android之GPS研究（实战篇一）

TI平台使用SIRF GPS

1.底层驱动的实现

GPS厂商提供的库通过echo sysfs的方式控制gps的onoff和reset，这需要linux实现GPS的sysfs模型驱动，在driver文件夹中增加gps.c文件

（1）填充一个bin_attribute的结构体，驱动加载后就会在系统的/sys/module目录下创建sirf文件

static struct bin_attribute sirf_mode_attr = {
    .attr = {
        .name = "sirf",
        .owner = THIS_MODULE,
        .mode = S_IRUGO | S_IWUGO,
    },
    .size = 0,
    .read = readcmd,
    .write = writecmd,
};

（2）probe函数

static int __init gps_probe(struct platform_device *pdev)
{
    int ret;
    ret = sysfs_create_bin_file(&(module_kset->kobj), &sirf_mode_attr);
    if (ret) {
            printk(KERN_ERR " Failed to create sys file\n");
        return -ENOMEM;
    }
    return 0;
}

（3）remove函数

static int __init gps_remove(struct platform_device *pdev)
{
    sysfs_remove_bin_file(&(module_kset->kobj), &sirf_mode_attr);

    return 0;
}

（4）平台驱动的注册

static struct platform_driver gps_driver = {
    .probe        = gps_probe,
    .remove        = gps_remove,
    .driver        = {
        .name    = "gps",
    },
};

static int __init gps_init(void)
{
    return platform_driver_register(&gps_driver);
}

static void __exit gps_exit(void)
{
    platform_driver_unregister(&gps_driver);
}

late_initcall(gps_init);
module_exit(gps_exit);

（5）write和read函数（read暂时为空，没有用到）

static ssize_t readcmd(struct kobject *kobj,
            struct bin_attribute *attr,
            char *buf, loff_t off, size_t count)
{
}

static ssize_t writecmd(struct kobject *kobj,
            struct bin_attribute *attr,
            char *buf, loff_t off, size_t count)
{
    char *tail;
    int op;
    op = simple_strtol(buf, &tail, 10);
    switch(op) {
        case 1:
        case 2:
            break;
        case 3:
            printk(KERN_BUG " Chip running...\n");
            set_power_on();
            run_mode = RUN_MODE;
            break;
        case 4:
            printk(KERN_BUG " Chip stopped...\n");
            set_power_off();
            run_mode = STOP_MODE;
            break;
        case 5:
            printk(KERN_BUG " Chip reset on high...\n");
            set_reset(1);
            break;
        case 6:
            printk(KERN_BUG " Chip reset on low...\n");
            set_reset(0);
            break;
        default:
            printk(KERN_BUG " Unknown operation %d\n", op);
            break;
    }
    return count;
}

现在通过echo number > /sys/module/sirf就能控制GPS的power on/off和reset。