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相关知识：Linux设备驱动开发

insmod 编译好的.ko文件后再运行beep_app.c编译完成的可执行文件即可使板子蜂鸣。

beep_drv.c:

#include <linux/module.h> //包含了加载模块时需要使用的大量符号和函数声明
#include <linux/kernel.h> //包含了printk内核打印函数等函数声明
#include <linux/init.h>  //包含了模块加载函数和模块释放函数的宏定义
#include <linux/errno.h>
#include <linux/cdev.h>
#include<linux/fs.h>
#include <linux/device.h>
#include <linux/ioport.h>
#include <linux/io.h>
#include <linux/uaccess.h>int devno_major=0;//beep的主设备号
int devno_minor=0;//beep的次设备号
struct class *beep_class;
struct device *beep_device;
struct resource *beep_resource;
void __iomem *gpioc_base_va;
void __iomem *gpiocout_va;    
void __iomem *gpiocoutenb_va; 
void __iomem *gpiocaltfn0_va; 
void __iomem *gpiocaltfn1_va; 
void __iomem *gpiocpad_va;    module_param(devno_major,int,0660);
module_param(devno_minor,int,0660);enum beep_state{BEEP_OFF,BEEP_ON};int beep_state=BEEP_OFF;/*1、定义一个字符设备 ---> struct cdev*/
struct cdev beep_cdev;/*2、定义并初始化字符设备的文件操作集 ---> struct file_operations*/
int gec6818_beep_open(struct inode *inode, struct file *filp)
{printk("beep have been opened!\n");return 0;
}
ssize_t gec6818_beep_read (struct file *filp, char __user *user_buf,size_t size, loff_t *off)
{int r = copy_to_user(user_buf, (void*)&beep_state, size);if(r != 0)return EINVAL;return size;
}
ssize_t gec6818_beep_write (struct file *filp, const char __user *user_buf, size_t size, loff_t *off)
{int r = copy_from_user((void*)&beep_state, user_buf, size);if(r != 0)return EINVAL;if(beep_state == BEEP_ON)writel(readl(gpiocout_va)|(0x01<<14),gpiocout_va);elsewritel(readl(gpiocout_va)&(~(0x01<<14)),gpiocout_va);return size;
}
int gec6818_beep_release (struct inode *inode, struct file *filp)
{printk("beep have been closed!\n");return 0;
}static const struct file_operations gec6818_beep_fops = {.owner = THIS_MODULE,.open = gec6818_beep_open,.read = gec6818_beep_read,.write = gec6818_beep_write,.release = gec6818_beep_release
};//入口函数 -->安装驱动
static int  __init gec6818_beep_init(void)
{dev_t devno;//beep的设备号int ret=0;/*3、给字符设备申请一个设备号 ---> 设备号=主设备号<<20 + 次设备号*/if(devno_major != 0){devno = MKDEV(devno_major,devno_minor);if(register_chrdev_region(devno, 1, "gec6818_beep")){printk("register_chrdev_region error!\n");if(alloc_chrdev_region(&devno, devno_minor, 1, "gec6818_beep")){printk("alloc_chrdev_region error!\n");ret = EINVAL;goto alloc_chrdev_region_err;}}}else{if(alloc_chrdev_region(&devno, devno_minor, 1, "gec6818_beep")){printk("alloc_chrdev_region error!\n");ret = EINVAL;goto alloc_chrdev_region_err;}}devno_major = MAJOR(devno);devno_minor = MINOR(devno);/*4、初始化字符设备*/cdev_init(&beep_cdev, &gec6818_beep_fops);/*5、将字符设备加入内核*/if(cdev_add(&beep_cdev, devno, 1)<0){ret = EINVAL;goto cdev_add_err;	}/*6、创建class*/beep_class = class_create(THIS_MODULE, "gec6818_beep");if(beep_class == NULL){ret = EBUSY;goto class_create_err;}/*7、创建device*/beep_device = device_create(beep_class, NULL,devno, NULL, "gec6818_beep");if(beep_device == NULL){ret = EBUSY;goto device_create_err;}/*8、申请物理内存区*/beep_resource = request_mem_region(0xC001C000, 0x1000, "GPIOC_MEM");if(beep_resource == NULL){ret = EBUSY;goto request_mem_region_err;}/*9、IO内存动态映射，得到虚拟地址*/gpioc_base_va = ioremap(0xC001C000, 0x1000);if(gpioc_base_va == NULL){ret = EBUSY;goto ioremap_err;}/*10、使用虚拟地址，把beep进行初始化*/gpiocout_va    = gpioc_base_va + 0x00;gpiocoutenb_va = gpioc_base_va + 0x04;gpiocaltfn0_va = gpioc_base_va + 0x20;gpiocaltfn1_va = gpioc_base_va + 0x24;gpiocpad_va    = gpioc_base_va + 0x18;//GPIOCALTFN0 &= ~(0x03<<28);//把GPIOC14设置为GPIO功能writel(readl(gpiocaltfn0_va)&(~(0x03<<28)),gpiocaltfn0_va);//GPIOCALTFN0 |= (0x01<<28);writel(readl(gpiocaltfn0_va)|((0x01<<28)),gpiocaltfn0_va);//GPIOCOUTENB |= 1<<14;//把GPIOC14设置为输出模式writel(readl(gpiocoutenb_va)|((0x01<<14)),gpiocoutenb_va);//GPIOCOUT &= ~(1<<14);//把GPIOC14输出低电平，默认beep不响writel(readl(gpiocout_va)&(~(0x01<<14)),gpiocout_va);printk("gec6818 beep init success!\n");return 0;
ioremap_err:release_mem_region(0xC001C000, 0x1000);
request_mem_region_err:device_destroy(beep_class, devno);
device_create_err:class_destroy(beep_class);
class_create_err:
cdev_add_err:unregister_chrdev_region(devno, 1);//注销设备号
alloc_chrdev_region_err:return ret;
}//出口函数 -->卸载驱动
static void __exit gec6818_beep_exit(void)
{iounmap(gpioc_base_va);release_mem_region(0xC001C000, 0x1000);device_destroy(beep_class, MKDEV(devno_major,devno_minor));class_destroy(beep_class);unregister_chrdev_region(MKDEV(devno_major,devno_minor), 1);//注销设备号printk("6818gec beep exit\n ");
}//驱动程序的入口: #insmod hello.ko ==> module_init() ==> gec6868_hello_init();
module_init(gec6818_beep_init);
//驱动程序的出口: #rmmod hello.ko ==> module_exit() ==> gec6818_hello_exit();
module_exit(gec6818_beep_exit);
//module的描述： #modinfo  hello.ko
MODULE_AUTHOR("[e-mail]");
MODULE_DESCRIPTION("beep driver for GEC6818");
MODULE_LICENSE("GPL");
MODULE_VERSION("V1.0");

 beep_app.c:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int beep_state;
int readbuf;int main()
{int fd = open("/dev/gec6818_beep",O_RDWR);if(fd == -1){printf("open failed!\n");return -1;}while(1){beep_state=1;int r = write(fd,&beep_state,4);if(r !=4 ){printf("write error!\n");}read(fd,&readbuf,4);printf("read buf is %d\n",readbuf);sleep(2);beep_state=0;write(fd,&beep_state,4);read(fd,&readbuf,4);printf("read buf is %d\n",readbuf);sleep(2);}
}

makefile:

#KERNELRELEASE这个变量，在内核源码的根目录下面的Makefile会初初始化的ifeq ($(KERNELRELEASE),)KERN_DIR := /home/china/6818GEC/kernel#在Makefile中可以调用shell的命令，调用方法如下:
# $(shell  shell命令) -> 整个这个表达式，表示调用该shell命令的输出结果
PWD := $(shell pwd)CROSS_COMPILE := /home/china/6818GEC/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/bin/arm-eabi-modules:make -C $(KERN_DIR)  M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE)  modules
clean:rm -rf *.orm -rf  modules.order  .tmp_versions *.ko  Module.symversrm -f  *.cmd .*.cmd  *.mod.celseobj-m += beep_drv.oendif