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linux驱动:[1]LED驱动/dev/led

linux驱动:[1]LED驱动/dev/led

LED Linux驱动程序

测试平台: Xunlong Orange Pi Zero

代码一览(解析见下方)

驱动程序以及Makefile如下:

  • sun8i_opizero_led.c:

    #include <linux/module.h>
    #include <linux/kernel.h>
    #include <linux/fs.h>
    #include <linux/device.h>
    #include <asm/uaccess.h>
    #include <asm/io.h>

    static struct class *sun8i_opizero_led_class;

    //STATUS-LED:PA17

    #define PIO_BASE 0x1C20800

    volatile unsigned long pacfg[4] = {NULL};
    volatile unsigned long
    padat = NULL;

    static int sun8i_opizero_led_open(struct inode inode, struct file file)
    {

    //configure pa17 to output mode
    *pacfg[2] &amp;= ~(3 &lt;&lt; 5);
    return 0;
    

    }

    static ssize_t sun8i_opizero_led_write(struct file file, const char __user buf, size_t count, loff_t *ppos)
    {

    int val;
    copy_from_user(&amp;val, buf, count);
    
    if (val == 1)
        *padat |= (1 &lt;&lt; 17);
    else
        *padat &amp;= ~(1 &lt;&lt; 17);
    
    return 0;
    

    }

    static struct file_operations sun8i_opizero_led_fops = {

    .owner = THIS_MODULE,
    .open = sun8i_opizero_led_open,
    .write = sun8i_opizero_led_write,
    

    };

    int major;

    int sun8i_opizero_led_init(void)
    {

    major = register_chrdev(0, "led", &amp;sun8i_opizero_led_fops);
    sun8i_opizero_led_class = class_create(THIS_MODULE, "led");
    device_create(sun8i_opizero_led_class, NULL, MKDEV(major, 0), NULL, "led");
    
    pacfg[0] = (volatile unsigned long *)ioremap(PIO_BASE, 0x20);
    pacfg[1] = pacfg[0] + 1;
    pacfg[2] = pacfg[1] + 1;
    pacfg[3] = pacfg[2] + 1;
    padat = pacfg[3] + 1;
    
    return 0;
    

    }

    static void sun8i_opizero_led_exit(void)
    {

    unregister_chrdev(major, "led");
    device_destroy(sun8i_opizero_led_class, MKDEV(major, 0));
    class_destroy(sun8i_opizero_led_class);
    iounmap(pacfg[0]);
    

    }

    module_init(sun8i_opizero_led_init);
    module_exit(sun8i_opizero_led_exit);

    MODULE_DESCRIPTION(“LED driver for Xunlong Orange Pi Zero”);
    MODULE_AUTHOR(“Techping Chan <techping.chan@gmail.com>”);
    MODULE_LICENSE(“GPL”);
    MODULE_ALIAS(“platform:orange-pi-zero-led”);
    `

  • Makefile:

    `obj-m := sun8i_opizero_led.o #编译进模块
    KERNELDIR := /lib/modules/3.4.113-sun8i/build #此处为linux内核库目录
    PWD := $(shell pwd) #获取当前目录
    OUTPUT := $(obj-m) $(obj-m:.o=.ko) $(obj-m:.o=.mod.o) $(obj-m:.o=.mod.c) modules.order Module.symvers

    modules:

    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
    

    clean:

    rm -rf $(OUTPUT)
    

    </pre> 在shell中使用以下命令装载驱动程序: <pre>$ make
    $ insmod sun8i_opizero_led.ko
    `
    使用linux c进行测试:

  • led_test.c:

    `#include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <stdio.h>

    int main(int argc, char **argv)
    {

    int fd, val = 1;
    fd = open("/dev/led", O_RDWR);
    
    if (fd &lt; 0)
        printf("can't open led device");
    
    if (argc != 2) {
        printf("Usage:\n");
        printf("%s &lt;on|off&gt;\n", argv[0]);
        return 1;
    }
    
    if (strcmp(argv[1], "on") == 0)
        val = 1;
    else
        val = 0;
    
    write(fd, &amp;val, 4);
    return 0;
    

    }
    </pre> **进行编译、测试:** <pre>$ gcc -o led_test led_test.c
    $ ./led_test on
    $ ./led_test off
    `
    没问题,成功操作LED!


    代码解析:

    写Linux驱动程序的步骤无非是:

  1. 驱动框架
  2. 硬件操作

    *   看原理图
    
    • 看数据手册
    • 编写代码
      这里编写的程序和单片机程序的区别就是:

    单片机一般不具备MMU(内存管理单元),使用的是物理地址,而现在的SoC一般都带有MMU,使用虚拟地址。这时候我们就需要用Linux C库提供的 ioremap 函数去将物理地址映射为虚拟地址。

    led_schematic

    通过查看原理图,我们得知LED(STATUS-LED)接在PA17处。

    pio_datasheet_0

    Port Controller Register 的物理基地址为0x01C20800,在 sun8i_opizero_led.c 中使用:

    pacfg[0] = (volatile unsigned long *)ioremap(PIO_BASE, 0x20);

    把PA_CFG0、PA_CFG1、……PA_PUL1这0x20字节物理地址映射到pacfg[0]~(paccfg[0] + 8)。

    之后的操作也是就跟操作单片机一样的位操作了。

    pio_datasheet_1

    `static int sun8i_opizero_led_open(struct inode inode, struct file file)
    {

    //configure pa17 to output
    *pacfg[2] &amp;= ~(3 &lt;&lt; 5);
    return 0;
    

    }
    </pre> ![pio_datasheet_2](http://upload-images.jianshu.io/upload_images/3653104-84b197d91f2200d9?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240) <pre>if (val == 1)

    *padat |= (1 &lt;&lt; 17);
    

    else

    *padat &amp;= ~(1 &lt;&lt; 17);
    

对硬件操作封装成固定的驱动程序框架格式,经过编译之后就可以注册到内核以待使用了。