zedboard 驱动理解

1 驱动程序的编写

  驱动是LINUX开发的必经之路，应用层对底层的调用经过了库与内核，内核下面才是驱动层，当你在应用程序执行对底层的控制时，驱动程序为你的控制提供了接口，或者说是策略。

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

#define DEVICE_NAME "PWM_MOUDLE"
#define PWM_MOUDLE_PHY_ADDR 0x6CA00000    //This Address is based XPS 这个地址ISE EDK中分配的地址就是硬件的东东啦

/* 描述驱动程序的一些信息，不是必须的 */
MODULE_AUTHOR("Xilinx XUP");             // 驱动程序的作者
MODULE_DESCRIPTION("PWM moudle dirver"); // 一些描述信息
MODULE_VERSION("v1.0");
MODULE_LICENSE("GPL");                   // 遵循的协议

static int pwm_driver_major;
static struct class* pwm_driver_class = NULL;
static struct device* pwm_driver_device = NULL;

unsigned long pwm_fre_addr = 0;		//pwm moulde's frequency visual address
unsigned long pwm_duty_addr = 0;	//pwm moulde's duty visual address
static long frequency=0;

/*这个结构是字符设备驱动的核心*/

static struct file_operations pwm_driver_fops = {
    .owner = THIS_MODULE,               /* 这是一个宏，推向编译模块时自动创建的__this_module变量 在Export.h (c:usersadministratordesktoplinux-3.3-digilentincludelinux):#define THIS_MODULE (&__this_module)*/
};

static ssize_t sys_pwm_frequency_set (struct device* dev, struct device_attribute* attr, const char* buf, size_t count)
{
    long value = 0;
    int i;
    frequency=0;
    outl(value,  pwm_fre_addr); //close pwm moudle before we modfiy the frequency

    for (i = 0; i < count-1; i++){
        frequency  *= 10;
        frequency += buf[i] - '0';
    }
    if(value>100000000) value=100000000;
    value=100000000/frequency;  // 100Mhz/frequency 100Mhz is set by XPS
	
    outl(value,  pwm_fre_addr);
    return count;
} 

static ssize_t sys_pwm_duty_set (struct device* dev, struct device_attribute* attr, const char* buf, size_t count) //duty cycle 
{
    long value = 0;
    int i;
//
	outl(value,  pwm_duty_addr); //close pwm moudle before we modfiy the duty cycle

    for (i = 0; i < count-1; i++){
        value  *= 10;
        value += buf[i] - '0';
    }
	if (value>100) value=100;
	value=100000000/frequency*value/100;
   
    if (value!= 0)
        value = value | 0x80000000;
    	outl(value,  pwm_duty_addr);

    return count;
} 

static DEVICE_ATTR(pwm_frequency, S_IWUSR, NULL, sys_pwm_frequency_set);
static DEVICE_ATTR(pwm_duty, S_IWUSR, NULL, sys_pwm_duty_set);

/* 执行insmod xxx.ko时就会执行pwm_driver_module_init（）函数 *

static int __init pwm_driver_module_init(void)
{
    int ret;
    /* 注册字符设备驱动程序
     * 参数为主设备号、设备名字、file_operations结构；
     * 这样，主设备号就和具体的file_operations结构联系起来了，
     * 操作主设备为BUTTON_MAJOR的设备文件时，就会调用s3c24xx_buttons_fops中的相关成员函数
     * BUTTON_MAJOR可以设为0，表示由内核自动分配主设备号
     */
    pwm_driver_major=register_chrdev(0, DEVICE_NAME, &pwm_driver_fops);//内核注册设备驱动
    if (pwm_driver_major < 0){
        printk("failed to register device.
");
        return -1;
    }

    pwm_driver_class = class_create(THIS_MODULE, "pwm_driver");        //创建PWM设备类
    if (IS_ERR(pwm_driver_class)){
        printk("failed to create pwm moudle class.
");
        unregister_chrdev(pwm_driver_major, DEVICE_NAME);
        return -1;
    }

    pwm_driver_device = device_create(pwm_driver_class, NULL, MKDEV(pwm_driver_major, 0), NULL, "pwm_device"); //利用pwm_driver设备类创建一个pwm_device
    if (IS_ERR(pwm_driver_device)){
        printk("failed to create device .
");
        unregister_chrdev(pwm_driver_major, DEVICE_NAME);
        return -1;
    }
   
    ret = device_create_file(pwm_driver_device, &dev_attr_pwm_frequency);       //在pwm_device设备中创建frequency与duty两个文件
    if (ret < 0)
        printk("failed to create pwm_frequency endpoint
");
    
    ret = device_create_file(pwm_driver_device, &dev_attr_pwm_duty);
    if (ret < 0)                                                                //将pwm模块的物理地址映射到虚拟地址上 也就是EDK中分配的地址
        printk("failed to create pwm_duty endpoint
");
   
   	pwm_fre_addr = (unsigned long)ioremap(PWM_MOUDLE_PHY_ADDR, sizeof(u32));//To get Custom IP--PWM moudle's virtual address
	pwm_duty_addr = pwm_fre_addr+4;		
        			
    printk(" pwm driver initial successfully!
");
    return 0;
}

/*
执行rmmod xxx.ko时就会执行pwm_driver_module_exit（）函数
*/

static void __exit pwm_driver_module_exit(void)
{
    device_remove_file(pwm_driver_device, &dev_attr_pwm_frequency);
    device_remove_file(pwm_driver_device, &dev_attr_pwm_duty);
    device_destroy(pwm_driver_class, MKDEV(pwm_driver_major, 0));
    class_unregister(pwm_driver_class);
    class_destroy(pwm_driver_class);
    unregister_chrdev(pwm_driver_major, DEVICE_NAME);
    printk("pwm module exit.
");
}

/* 这两行指定驱动程序的初始化函数和卸载函数 */

module_init(pwm_driver_module_init);
module_exit(pwm_driver_module_exit);

2驱动程序的编译

 makefile编写

  ifneq ($(KERNELRELEASE),)
  obj-m := pwm_driver.o
  else
  KERNEL_DIR := <YOUR_DIR>/ZedBoard/Kernel/Digilent-linux-3.3
  PWD := $(shell pwd)
  all:
	$(MAKE) -C $(KERNEL_DIR) SUBDIRS=$(PWD) modules ARCH=arm
  clean:
	rm *.o *.ko *.mod.c
  endif

<YOUR_DIR>/ZedBoard/Kernel/Digilent-linux-3.3 是你的路径
最后make 生成pwm_driver.ko 拷贝到zedboard文件系统上

3 驱动程序的测试

   加载驱动

   insmod pwm_driver.ko在/dev/ 下可以找到我们注册的设备 pwm_device

  进入/sys/class/..目录  

  在zedboard 的shell上执行 echo 1000 > pwm_frequency  

                             echo 50    > pwm_duty