使用linux内核hrtimer高精度定时器实现GPIO口模拟PWM,【原创】

关键词：Android  linux hrtimer 蜂鸣器  等待队列 信号量 字符设备

平台信息:
内核：linux3.4.39 
系统：android/android5.1
平台：S5P4418 

作者：庄泽彬(欢迎转载，请注明作者)

邮箱：2760715357@qq.com

程序描述：本文控制的设备是无源蜂鸣器，由于无源蜂鸣器是需要产生一定的频率的PWM才能够控制蜂鸣器，不像有源蜂鸣器，只需要提供高低电平就可以控制蜂鸣器。linux内核普通的定时器，由于具有一定的局限性，不能达到纳秒级别的定时，使用普通的定时器模拟GPIO口产生PWM会导致蜂鸣器出现杂音，因此要使用hrtimer高精度定时器模拟GPIO口产生PWM可以极大的改善性能。使用信号量sem只是为了避免多个应用程序打开设备，使用等待队列是为了让程序可以按照指定的方式去运行，如果不加等待队列，在启动hrtimer定时器之后就会不会等待定时器完成之后在关闭设备，因此需要加入等待队列，等待定时器定时的工作完成之后再唤醒等待队列。虽然程序可以使用GPIO模拟PWM产生一定频率的信号去控制无源蜂鸣器，但是还是存在一定的局限性，因为定时器也是加入内核进行调度，所以有可能杂定时的时候会导致输出的PWM被打断，导致杂音的出现。因此严格来说不能完整的输出一段不被打断模拟PWM信号。如果有什么好方法可以实现的话，可以共同探讨。好吧不说了上代码吧。

无源蜂鸣器的驱动程序(代码写的一般般如有不对，欢迎指点)

buzzer_driver.c

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/device.h>
 #include <linux/slab.h>
 #include <linux/cdev.h>
 #include <linux/interrupt.h>
 #include <linux/gpio.h>
 #include <linux/input.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/delay.h>
 #include <linux/semaphore.h>

 #include <asm/uaccess.h>
 #include <asm/io.h>

 #include <mach/platform.h>

 #define BUZZER_DEVICE_NAME   "mybuzzer"
 #define BUZZER_CLASS_NAME   "mybuzzer"    //sys/class/mybuzzer
 #define BUZZER_DEVICE_NUM     1         //设备节点的编号最终生成节点的名字为/dev/buzzer-1

 #define BUZZER_GPIO_SWITCH  1    //是否设置buzzer的gpio的初始化，另一个驱动已经初始化GPIO
 #define BUZZER_DELAY_TIME_HIGHT (190000) //2.7KHZ
 #define BUZZER_DELAY_TIME_LOW (190000) //2.7KHZ
 #define DE_BUG 1

 #if DE_BUG
 #define prdebug(fmt,arg...)      printk("zbzhuang"KERN_ERR fmt"\n",##arg)
 #else
 #define prdebug(fmt,arg...)      do{}while(0);
 #endif

 typedef enum {
     BUZZER_DISABLE = ,
     BUZZER_ENABLE,
 }BUZZER_STATUS_t;

 //buzzer的设备对象
 struct buzzer_chip{
     dev_t devno;
     struct cdev *cdev;
     struct class *cls;
     struct device *dev;
     unsigned long count; //从应用空间读取的数据
     struct semaphore sem;
     struct hrtimer mytimer;
     ktime_t kt;     //设置定时时间
     wait_queue_head_t wait_queue;
     BUZZER_STATUS_t status;
 };

 static int count = ;
 struct buzzer_chip *buzzer_dev;

 static void buzzer_test(void);
 static void buzzer_gpio_start(void);
 static enum hrtimer_restart    hrtimer_handler(struct hrtimer *timer);

 int buzzer_drv_open (struct inode * inode, struct file *filp)
 {
     int minor;
     int major;

     prdebug("--------------%s----------------",__func__);

     minor = iminor(inode);
     major = imajor(inode);

     prdebug("\r\nmajor = %d minor = %d\rn",major,minor);
     filp->private_data = (void *)minor;

     if(down_interruptible(&buzzer_dev->sem))
         return -ERESTARTSYS;

     return ;
 }
 ssize_t buzzer_drv_read (struct file *filp, char __user *userbuf, size_t count, loff_t *fpos)
 {
     int ret;

     prdebug("--------------%s----------------",__func__);

     if(filp->f_flags & O_NONBLOCK){
         return -EAGAIN;
     }

     ret = copy_to_user(userbuf,&buzzer_dev->count,count);
     if(ret > ){
         prdebug("error copy_to_user");
         return -EFAULT;
     }
     prdebug("%s :read count = %ld",__func__,buzzer_dev->count);

     return count;
 }
 ssize_t buzzer_drv_write (struct file *filp, const char __user *userbuf, size_t count, loff_t *fpos)
 {
     int ret;

     prdebug("--------------%s----------------",__func__);
     prdebug("task pid[%d] context[%s]",current->pid,current->comm);

     ret = copy_from_user(&buzzer_dev->count,userbuf,count);
     if(ret > ){
         prdebug("error copy_from_user");
         return -EFAULT;
     }

     prdebug("%s :write count = %ld",__func__,buzzer_dev->count);

     if(buzzer_dev->count){
         if(buzzer_dev->status == BUZZER_DISABLE){
             //启动定时器
             prdebug("-----------start hrtimer timer-------------");
             buzzer_dev->status = BUZZER_ENABLE;
             buzzer_gpio_start();
             wait_event(buzzer_dev->wait_queue, buzzer_dev->status == BUZZER_DISABLE);
             prdebug("------------wake up queue-------------------------------");
         }else{
             prdebug("buzzer_aready work");
         }

     }else{

     }

     return count;

 }
 int buzzer_drv_close (struct inode *inode, struct file *filp)
 {

     prdebug("--------------%s----------------",__func__);
     up(&buzzer_dev->sem);

     return ;

 }

 const struct file_operations buzzer_fops = {
     .open = buzzer_drv_open,
     .write = buzzer_drv_write,
     .read = buzzer_drv_read,
     .release = buzzer_drv_close,

 };

 static int buzzer_gpio_init(void)
 {
     int ret = -;

     if(gpio_request(BUZZER_IO, "BUZZER_GPIO")){
         prdebug("error buzzer_gpio_init");
         return ret;

     }else{
         gpio_direction_output(BUZZER_IO, );
         gpio_set_value(BUZZER_IO, );
         buzzer_dev->status = BUZZER_DISABLE;
     }

     return ;

 }

 static void buzzer_gpio_exit(void)
 {
     gpio_set_value(BUZZER_IO, );
     gpio_free(BUZZER_IO);
 }

 static void buzzer_gpio_start(void)
 {
     prdebug("-----------buzzer_gpio_start------------");

     //高精度定时器
     hrtimer_init(&buzzer_dev->mytimer,CLOCK_MONOTONIC,HRTIMER_MODE_REL);
     buzzer_dev->mytimer.function = hrtimer_handler;
     buzzer_dev->kt = ktime_set(, BUZZER_DELAY_TIME_LOW);
     hrtimer_start(&buzzer_dev->mytimer,buzzer_dev->kt,HRTIMER_MODE_REL);

 }

 static void buzzer_test(void)
 {
     unsigned long i;

     prdebug("-----------start test buzzer------------");
         for(i = ;i < ;i ++){
             gpio_set_value(BUZZER_IO, );
             udelay();
             gpio_set_value(BUZZER_IO, );
             udelay();
         }
     prdebug("-----------end test buzzer------------");
 }

 static enum hrtimer_restart    hrtimer_handler(struct hrtimer *timer)
 {

     //prdebug("--------------%s----------------",__func__);

     if(buzzer_dev->count != ){

         if (gpio_get_value(BUZZER_IO) == ) {
             gpio_set_value(BUZZER_IO, );

             buzzer_dev->kt = ktime_set(, BUZZER_DELAY_TIME_LOW);
             hrtimer_forward_now(&buzzer_dev->mytimer, buzzer_dev->kt);

         } else {
             gpio_set_value(BUZZER_IO, );

             buzzer_dev->kt = ktime_set(, BUZZER_DELAY_TIME_HIGHT);
             hrtimer_forward_now(&buzzer_dev->mytimer, buzzer_dev->kt);
         }
         buzzer_dev->count --;
         return HRTIMER_RESTART;
     }else{
         buzzer_dev->count --;
         buzzer_dev->status = BUZZER_DISABLE;
         prdebug("buzzer_dev->count = %d",buzzer_dev->count);
         prdebug("-----------finsh hrtimer timer-------------");
         wake_up(&buzzer_dev->wait_queue);
         return HRTIMER_NORESTART;
     }

 }

 static int __init buzzer_drv_init(void)
 {
     int ret;

     prdebug("--------------%s----------------",__func__);

     buzzer_dev = kzalloc(sizeof(struct buzzer_chip),GFP_KERNEL);
     if(buzzer_dev == NULL){
         prdebug("kzalloc error");
         return -ENOMEM;
     }

     //动态的申请设备号
     ret = alloc_chrdev_region(&buzzer_dev->devno,,,BUZZER_DEVICE_NAME);
     if(ret != ){
         prdebug("error alloc_chrdev_region");
         goto err_free;
     }

     //分配cdev对象
     buzzer_dev->cdev = cdev_alloc();
     cdev_init(buzzer_dev->cdev,&buzzer_fops);
     cdev_add(buzzer_dev->cdev,buzzer_dev->devno,);

     //自动创建设备节点
     buzzer_dev->cls = class_create(THIS_MODULE,BUZZER_CLASS_NAME);
     if(IS_ERR(buzzer_dev->cls)){
         prdebug("error class_create");
         ret = PTR_ERR(buzzer_dev->cls);
         goto err_unregister;
     }

     buzzer_dev->dev = device_create(buzzer_dev->cls,NULL,buzzer_dev->devno,NULL,"buzzer-%d",BUZZER_DEVICE_NUM);
     if(IS_ERR(buzzer_dev->dev)){
         prdebug("error device_create");
         ret = PTR_ERR(buzzer_dev);
         goto err_class_error;
     }

     //信号量
     sema_init(&buzzer_dev->sem,);

     init_waitqueue_head(&buzzer_dev->wait_queue);

 #if BUZZER_GPIO_SWITCH
     //初始化Buzzer的GPIO
     ret = buzzer_gpio_init();
     if(ret !=){
         prdebug("error buzzer_gpio_init");
         goto err_device_create;
     }

 #endif

     return ;

 #if BUZZER_GPIO_SWITCH
 err_device_create:
     device_destroy(buzzer_dev->cls,buzzer_dev->devno);
 #endif

 err_class_error:
     class_destroy(buzzer_dev->cls);

 err_unregister:
     cdev_del(buzzer_dev->cdev);
     unregister_chrdev_region(buzzer_dev->devno,);

 err_free:
     kfree(buzzer_dev);
     return ret;

 }

 static void __exit buzzer_drv_exit(void)
 {
     prdebug("--------------%s----------------",__func__);
 #if BUZZER_GPIO_SWITCH
     buzzer_gpio_exit();
 #endif
     device_destroy(buzzer_dev->cls,buzzer_dev->devno);
     class_destroy(buzzer_dev->cls);
     cdev_del(buzzer_dev->cdev);
     unregister_chrdev_region(buzzer_dev->devno,);
     kfree(buzzer_dev);

 }

 module_init(buzzer_drv_init);
 module_exit(buzzer_drv_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("zhuang zebin@qq.com");

驱动程序对应的Makefile，自己修改交叉工具链还有内核的位置

CROSS_COMPILE = /home/zsf/u4209/s5p4418-5.1-android/trunk/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/bin/arm-eabi-
#CROSS_COMPILE = /home/zsf/book/toolchain-4.5.-farsight/bin/arm-none-linux-gnueabi-
CC = $(CROSS_COMPILE)gcc
#APP_NAME = led_app
MODULE_NAME = buzzer_driver

#内核源码路径
#KERNEL_DIR = /home/zsf/rk3188_5./android/kernel
KERNEL_DIR = /home/zsf/u4209/s5p4418-5.1-android/trunk/kernel

CUR_DIR = $(shell pwd)

all :
    make -C $(KERNEL_DIR) M=$(CUR_DIR) modules
    #$(CC) $(APP_NAME).c -o  $(APP_NAME)

clean :
    make -C $(KERNEL_DIR) M=$(CUR_DIR) clean
    #rm -rf $(APP_NAME) 

install:
    cp -raf  *.ko $(APP_NAME)  /opt/rootfs/drv_module/

#指定编译哪个源文件
obj-m = $(MODULE_NAME).o

~

写一个简单的APP去控制设备代码如下buzzer_write.c：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc,char **argv)
{
    int fd = -;
    unsigned long  on = -;

    fd = open("/dev/buzzer-1",O_RDWR);
    if(fd < ){
        perror("open");
        exit();
    }

    on = atol(argv[]);
    write(fd,&on,);

    close(fd);

    return ;
}

对应的Android.mk

 LOCAL_PATH := $(call my-dir)

 include $(CLEAR_VARS)

 LOCAL_MODULE_TAGS := optional

 LOCAL_MODULE := buzzer_write

 LOCAL_SRC_FILES := buzzer_write.cpp

 include $(BUILD_EXECUTABLE)

编译驱动：错误和警告可以忽略，之后使用adb工具将buzzer_driver.ko推送进板子。

编译应用程序

实验操作如下：

查看相应的LOG

这里无法展示你们看，蜂鸣器的叫声，经过测试改程序勉强还是可以使用的啊。