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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] &= ~(3 << 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(&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”, &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 $(OUTPUT)
    `
    在shell中使用以下命令装载驱动程序:
    `$ 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 < 0)
            printf("can't open led device");
    
        if (argc != 2) {
            printf("Usage:\n");
            printf("%s <on|off>\n", argv[0]);
            return 1;
        }
    
        if (strcmp(argv[1], "on") == 0)
            val = 1;
        else
            val = 0;
    
        write(fd, &val, 4);
        return 0;
    }
    `
    进行编译、测试:
    `$ 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

    led_schematic

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

    pio_datasheet_0

    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] &= ~(3 << 5);
        return 0;
    }
    `
    pio_datasheet_2

    `if (val == 1) padat |= (1 << 17); else padat &= ~(1 << 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。


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