驱动程序中调用的内核函数，在 4.x 版本的内核里都是一样的
LED驱动编写详细步骤如下：

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

需要注意的是：
- 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。

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

即使传入的是4byte大小也将会映射成4096一页的大小
不再使用该段虚拟地址时，要 iounmap(virt_addr)：
- 为什么需要ioremap？
运行程序两次，那么在内存中必定会由两份代码
同一个程序，运行时打印的全局变量的地址应该是一样的才对；但是运行两次实际内存保存的是两份代码，即两者全局变量在内存中的物理地址是不同的；显然，程序中打印的不是物理地址，而是CPU看到的虚拟地址
CPU使用同一个地址来访问同时运行的两个程序；根据不同的pid进程号进而访问不同的物理地址
使用MMU来实现虚拟地址到物理地址的转换
内核发出一个地址，能不能访问到硬件也是由MMU来决定的；mmu需要把物理地址映射成虚拟地址，内核才能使用虚拟地址来访问硬件
- volatile的使用
为了避免编译器自动优化，需要加上 volatile，告诉它“这是容易出错的，别乱优化”

volatile int *p = ioremap(xxxx, 4); // GPIO 寄存器的地址

每个单板所使用的Linux内核、头文件可能不一样，在编写makefile时需指定对应board内核的目录，在对应的内核中编译

修改board结构体

struct led_operations {
int num;                                /* LED灯的数量 */
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 */
int (*exit) (int which);                /* 退出LED */
};

修改board的LED操作代码 ```c
include

include “led_opr.h”

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)
{
    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;

}

         * 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;

}

/ 自己添加的 / static int board_demo_led_exit(int which) { if (which == 0) { board_demo_led_ctl(which, 0); / 将相关寄存器的值恢复为默认 / //不去设置 b[31:30]，GPIO5 也是默认使能的

    /* 取消映射 */
    iounmap( CCM_CCGR1                                );
    iounmap( IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3  );
    iounmap( GPIO5_GDIR                               );
    iounmap( GPIO5_DR                                 );
}
return 0;

} static struct led_operations board_demo_led_opr = { .num = 1, .init = board_demo_led_init, .ctl = board_demo_led_ctl, .exit = board_demo_led_exit, };

struct led_operations *get_board_led_opr(void) { return &board_demo_led_opr; }


- 在leddrv.c的open函数中调用led_operations的init，close函数中调用led_operations的exit
```c
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)
{
       int minor = iminor(node);
    printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
    p_led_opr->exit(minor);
    return 0;
}

使用 QEMU 模拟的硬件，它的硬件资源可以随意扩展。
IMX6ULL-QEMU代码 ```c struct iomux { volatile unsigned int unnames[23]; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO00; / offset 0x5c/ volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO01; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO02; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO04; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO05; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO06; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO07; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO08; volatile unsigned int IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO09; };

struct imx6ull_gpio { volatile unsigned int dr; volatile unsigned int gdir; volatile unsigned int psr; volatile unsigned int icr1; volatile unsigned int icr2; volatile unsigned int imr; volatile unsigned int isr; volatile unsigned int edge_sel; };

/ enable GPIO1,GPIO5 / static volatile unsigned int *CCM_CCGR1;

/ set GPIO5_IO03 as GPIO / static volatile unsigned int *IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3;

static struct iomux *iomux;

static struct imx6ull_gpio gpio1; static struct imx6ull_gpio gpio5;

static int board_demo_led_init (int which) / 初始化LED, which-哪个LED /
{ if (!CCM_CCGR1) { CCM_CCGR1 = ioremap(0x20C406C, 4); IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3 = ioremap(0x2290014, 4);

    iomux = ioremap(0x20e0000, sizeof(struct iomux));
    gpio1 = ioremap(0x209C000, sizeof(struct imx6ull_gpio));
    gpio5 = ioremap(0x20AC000, sizeof(struct imx6ull_gpio));
}
if (which == 0)
{
    /* 1. enable GPIO5 
     * CG15, b[31:30] = 0b11
     */
    *CCM_CCGR1 |= (3<<30);
    /* 2. set GPIO5_IO03 as GPIO 
     * MUX_MODE, b[3:0] = 0b101
     */
    *IOMUXC_SNVS_SW_MUX_CTL_PAD_SNVS_TAMPER3 = 5;
    /* 3. set GPIO5_IO03 as output 
     * GPIO5 GDIR, b[3] = 0b1
     */
    gpio5->gdir |= (1<<3);
}
else if(which == 1)
{
    /* 1. enable GPIO1 
     * CG13, b[27:26] = 0b11
     */
    *CCM_CCGR1 |= (3<<26);
    /* 2. set GPIO1_IO03 as GPIO 
     * MUX_MODE, b[3:0] = 0b101
     */
    iomux->IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03 = 5;
    /* 3. set GPIO1_IO03 as output 
     * GPIO1 GDIR, b[3] = 0b1
     */
    gpio1->gdir |= (1<<3);
}
else if(which == 2)
{
    /* 1. enable GPIO1 
     * CG13, b[27:26] = 0b11
     */
    *CCM_CCGR1 |= (3<<26);
    /* 2. set GPIO1_IO05 as GPIO 
     * MUX_MODE, b[3:0] = 0b101
     */
    iomux->IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO05 = 5;
    /* 3. set GPIO1_IO05 as output 
     * GPIO1 GDIR, b[5] = 0b1
     */
    gpio1->gdir |= (1<<5);
}
else if(which == 3)
{
    /* 1. enable GPIO1 
     * CG13, b[27:26] = 0b11
     */
    *CCM_CCGR1 |= (3<<26);
    /* 2. set GPIO1_IO06 as GPIO 
     * MUX_MODE, b[3:0] = 0b101
     */
    iomux->IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO06 = 5;
    /* 3. set GPIO1_IO06 as output 
     * GPIO1 GDIR, b[6] = 0b1
     */
    gpio1->gdir |= (1<<6);
}
//printk("%s %s line %d, led %d\n", __FILE__, __FUNCTION__, __LINE__, which);
return 0;

}

static int boarddemoledctl (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 / gpio5->dr &= ~(1<<3); else /* on : output 1 */ gpio5->dr |= (1<<3); } else if (which == 1) { if (status) /* on : output 0 */ gpio1->dr &= ~(1<<3); else /* on : output 1 */ gpio1->dr |= (1<<3); } else if (which == 2) { if (status) /* on : output 0 */ gpio1->dr &= ~(1<<5); else /* on : output 1 */ gpio1->dr |= (1<<5); } else if (which == 3) { if (status) /* on : output 0 */ gpio1->dr &= ~(1<<6); else /* on : output 1 */ gpio1->dr |= (1<<6); } return 0; }

static struct led_operations board_demo_led_opr = { .num = 4, .init = board_demo_led_init, .ctl = board_demo_led_ctl, };

struct led_operations *get_board_led_opr(void) { return &board_demo_led_opr; } ```

嵌入式

IMX6ULL的LED驱动程序

include

include “led_opr.h”