本节主要是完善上一篇没有写入实际的寄存器操作。
写LED驱动程序步骤：
① 看原理图确定引脚，确定引脚输出什么电平才能点亮/熄灭LED
② 看主芯片手册，确定寄存器操作方法：哪些寄存器？哪些位？地址是？
③ 编写驱动：先写框架，再写硬件操作的代码
注意：在芯片手册中确定的寄存器地址被称为物理地址，在Linux内核中无法直接使用。
??????需要使用内核提供的ioremap把物理地址映射为虚拟地址，使用虚拟地址。
ioremap函数的使用：
把物理地址phys_addr开始的一段空间(大小为size)，映射为虚拟地址；返回值是该段虚拟地址的首地址。
virt_addr ?=? ioremap(phys_addr, size);
实际上，它是按页(4096字节)进行映射的，是整页整页地映射的。
假设phys_addr = 0x10002，size=4，ioremap的内部实现是：
a. phys_addr按页取整，得到地址0x10000
b. size按页取整，得到4096
c. 把起始地址0x10000，大小为4096的这一块物理地址空间，映射到虚拟地址空间，
???假设得到的虚拟空间起始地址为0xf0010000
d. 那么phys_addr = 0x10002对应的virt_addr = 0xf0010002
不再使用该段虚拟地址时，要iounmap(virt_addr)：
以下是具体单板的代码：
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <asm/io.h>
#include "led_opr.h"
//使用指针进行操作
static volatile unsigned int *CCM_CCGR1 ;
static volatile unsigned int *IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3;
static volatile unsigned int *GPIO5_GDIR ;
static volatile unsigned int *GPIO5_DR ;
static int board_demo_led_init (int which) /* 初始化LED, which-哪个LED */
{
unsigned int val;
//printk("%s %s line %d, led %d\n", __FILE__, __FUNCTION__, __LINE__, which);
if (which == 0) //使用对某个LED使能
{
if (!CCM_CCGR1)
{
CCM_CCGR1 = ioremap(0x20C406C, 4);
IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3 = ioremap(0x2290014, 4);
GPIO5_GDIR = ioremap(0x020AC000 + 0x4, 4);
GPIO5_DR = ioremap(0x020AC000 + 0, 4);
}
/* GPIO5_IO03 */
/* a. 使能GPIO5
* set CCM to enable GPIO5
* CCM_CCGR1[CG15] 0x20C406C
* bit[31:30] = 0b11
*/
*CCM_CCGR1 |= (3<<30);
/* b. 设置GPIO5_IO03用于GPIO
* set IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3
* to configure GPIO5_IO03 as GPIO
* IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3 0x2290014
* bit[3:0] = 0b0101 alt5
*/
val = *IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3;
val &= ~(0xf);
val |= (5);
*IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3 = val;
/* b. 设置GPIO5_IO03作为output引脚
* set GPIO5_GDIR to configure GPIO5_IO03 as output
* GPIO5_GDIR 0x020AC000 + 0x4
* bit[3] = 0b1
*/
*GPIO5_GDIR |= (1<<3);
}
return 0;
}
static int board_demo_led_ctl (int which, char status) /* 控制LED, which-哪个LED, status:1-亮,0-灭 */
{
//printk("%s %s line %d, led %d, %s\n", __FILE__, __FUNCTION__, __LINE__, which, status ? "on" : "off");
if (which == 0)
{
if (status) /* on: output 0*/
{
/* d. 设置GPIO5_DR输出低电平
* set GPIO5_DR to configure GPIO5_IO03 output 0
* GPIO5_DR 0x020AC000 + 0
* bit[3] = 0b0
*/
*GPIO5_DR &= ~(1<<3);
}
else /* off: output 1*/
{
/* e. 设置GPIO5_IO3输出高电平
* set GPIO5_DR to configure GPIO5_IO03 output 1
* GPIO5_DR 0x020AC000 + 0
* bit[3] = 0b1
*/
*GPIO5_DR |= (1<<3);
}
}
return 0;
}
static struct led_operations board_demo_led_opr = {
.num = 1, //对多少个LED进行初始化，在drv中为其创建设备节点
.init = board_demo_led_init,
.ctl = board_demo_led_ctl,
};
struct led_operations *get_board_led_opr(void)
{
return &board_demo_led_opr;
}
以下是drv代码
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include "led_opr.h"
/* 1. 确定主设备号 */
static int major = 0;
static struct class *led_class;
struct led_operations *p_led_opr;
#define MIN(a, b) (a < b ? a : b)
/* 3. 实现对应的open/read/write等函数，填入file_operations结构体 */
static ssize_t led_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
return 0;
}
/* write(fd, &val, 1); */
static ssize_t led_drv_write (struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
int err;
char status;
struct inode *inode = file_inode(file);
int minor = iminor(inode);
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
err = copy_from_user(&status, buf, 1);
/* 根据次设备号和status控制LED */
p_led_opr->ctl(minor, status);
return 1;
}
static int led_drv_open (struct inode *node, struct file *file)
{
int minor = iminor(node);
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
/* 根据次设备号初始化LED */
p_led_opr->init(minor);
return 0;
}
static int led_drv_close (struct inode *node, struct file *file)
{
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
return 0;
}
/* 2. 定义自己的file_operations结构体 */
static struct file_operations led_drv = {
.owner = THIS_MODULE,
.open = led_drv_open,
.read = led_drv_read,
.write = led_drv_write,
.release = led_drv_close,
};
/* 4. 把file_operations结构体告诉内核：注册驱动程序 */
/* 5. 谁来注册驱动程序啊？得有一个入口函数：安装驱动程序时，就会去调用这个入口函数 */
static int __init led_init(void)
{
int err;
int i;
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
major = register_chrdev(0, "100ask_led", &led_drv); /* /dev/led */
led_class = class_create(THIS_MODULE, "100ask_led_class");
err = PTR_ERR(led_class);
if (IS_ERR(led_class)) {
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
unregister_chrdev(major, "led");
return -1;
}
p_led_opr = get_board_led_opr();
for (i = 0; i < p_led_opr->num; i++)
device_create(led_class, NULL, MKDEV(major, i), NULL, "100ask_led%d", i); /* /dev/100ask_led0,1,... */
return 0;
}
/* 6. 有入口函数就应该有出口函数：卸载驱动程序时，就会去调用这个出口函数 */
static void __exit led_exit(void)
{
int i;
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
for (i = 0; i < p_led_opr->num; i++)
device_destroy(led_class, MKDEV(major, i)); /* /dev/100ask_led0,1,... */
device_destroy(led_class, MKDEV(major, 0));
class_destroy(led_class);
unregister_chrdev(major, "100ask_led");
}
/* 7. 其他完善：提供设备信息，自动创建设备节点 */
module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");
以下是led.h
#ifndef _LED_OPR_H
#define _LED_OPR_H
struct led_operations {
int num; //有多少个LED
int (*init) (int which); /* 初始化LED, which-哪个LED */
int (*ctl) (int which, char status); /* 控制LED, which-哪个LED, status:1-亮,0-灭 */
};
struct led_operations *get_board_led_opr(void);
#endif