OK6410A学习笔记三：嵌入式Linux驱动之LED驱动

开发环境：
Windows7 + vmware workstation 6.5 + Ubuntu9.10
Linux Source Code: FORLINX_linux-3.0.1.tar.gz
ARM CROSS GCC: arm-linux-gcc v4.3.2

源码：
//s3c6410_led.c – driver file
#include#include#include#include#include
#define DEV_MAJOR 176
#define DEV_NAME “s3c6410_leds”


#define GPMCON 0x7F008820
#define GPMDAT 0x7F008824
#define GPMPUD 0x7F008828


volatile unsigned long *gpmcon = NULL;
volatile unsigned long *gpmdat = NULL;
volatile unsigned long *gpmpud = NULL;


static int s3c6410_led_open(struct inode *inode, struct file *filp)
{
//int ret;

printk(KERN_ALERT “This is open function of s3c6410 led driver.\n”);

*gpmpud &= 0xffffffaa; //set GPM0~3 as pull up enabled
*gpmcon &= 0xffff1111; //set GPM0~3 as output
*gpmdat &= 0xfffffff0; //set GPM0~3 to low level, which turn on leds

return 0;

}

static ssize_t s3c6410_led_write(struct file *filp,const char __user *buf,size_t count,loff_t *ppos)
{
int val;

//copy_from_user(&val,buf,count);

printk(KERN_ALERT “This is write function of s3c6410 led driver.\n”);

return count;
}


struct file_operations s3c6410_led_flops = {
.owner = THIS_MODULE,
.open = s3c6410_led_open,
.write = s3c6410_led_write,
};

static int __init s3c6410_led_init(void)
{
int ret;

//register led device driver into kernel
ret = register_chrdev(DEV_MAJOR,DEV_NAME,&s3c6410_led_flops);

//retriver the vritual address by ioremap
gpmcon = (volatile unsigned long *)ioremap(GPMCON,4); //32-bit reg
gpmdat = gpmcon + 1;
gpmpud = gpmcon + 2;

return 0;
}

static void __exit s3c6410_led_exit(void)
{
//unregister led device dirver from kernel
unregister_chrdev(DEV_MAJOR,DEV_NAME);

//iounmap
iounmap(gpmcon);
}

module_init(s3c6410_led_init);
module_exit(s3c6410_led_exit);

MODULE_DESCRIPTION(“This is led driver sample for OK6410A board.”);
MODULE_VERSION(“1.0”);
MODULE_AUTHOR(“”);
MODULE_LICENSE(“Dual BSD/GPL”);

//s3c6410_led_test.c – test file
#include
#include

int main(int argc,char* argv[])
{
int fd;

fd = open(“/dev/s3c6410_led”,0);

if(!fd){
printf(“open s3c6410 led failed.\n”);
}else{
printf(“open s3c6410 led succeed.\n”);
}
return 0;
}

解析：
1. 检查OK6410A开发板原理图，4个LED灯接在GPM0~3四个GPIO上。
2. 检查Samsung S3C6410X User’s Manual.pdf ，检查GPm端口操作阐明，包含GPMCON，GPMDAT，GPMPUD三个寄存器的基地址以及装备信息，然后确认点亮LED灯和平息LED灯的操作。
3. 编写源代码，包含驱动源码和测验源码。这儿比较重要的当地是，Linux驱动是作业在保护模式下，无法直接操作寄存器，因而必须将过程二中找到的寄存器基地址经过IO地址重映射，然后得到虚拟地址进行操作，在驱动程序进口函数中运用ioremap()函数进行地址重映射，在退出函数中运用iounmap()完毕地址重映射。别的，假如想在加载驱动的一起，让体系主动新建造备节点，则要将设备信息供给给体系内核，Linux体系支撑的mdev机制会依据驱动程序供给的信息新建造备节点。在上述源码中并没有完成这一功用。
4. 编译源码
驱动程序Makefile如下：
obj-m:=s3c6410_led.o
KERNELDIR?=/usr/src/linux-3.0.1

default:
$(MAKE) -C $(KERNELDIR) M=$(shell pwd) modules

clean:
rm -rf *.o *~ *.ko *.mod.c *.order *.symvers

在终端下履行如下指令:
#make //编译驱动程序，得到s3c6410_led.ko文件
#arm-linux-gcc s3c6410_led_test.c –o s3c6410_led_test //编译测验源码

5. 复制s3c6410_led.ko和s3c6410_led_test到SD卡中，给开发板上电