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 = 0,
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 = 1000;
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 0;
}
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 > 0){
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 > 0){
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 0;

}

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 = -1;

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

}else{
gpio_direction_output(BUZZER_IO, 1);
gpio_set_value(BUZZER_IO, 1);
buzzer_dev->status = BUZZER_DISABLE;
}

return 0;

}

static void buzzer_gpio_exit(void)
{
gpio_set_value(BUZZER_IO, 1);
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(0, 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 = 0;i < 10000;i ++){
gpio_set_value(BUZZER_IO, 0);
udelay(150);
gpio_set_value(BUZZER_IO, 1);
udelay(150);
}
prdebug("-----------end test buzzer------------");
}

static enum hrtimer_restart    hrtimer_handler(struct hrtimer *timer)
{

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

if(buzzer_dev->count != 1){

if (gpio_get_value(BUZZER_IO) == 1) {
gpio_set_value(BUZZER_IO, 0);

buzzer_dev->kt = ktime_set(0, BUZZER_DELAY_TIME_LOW);
hrtimer_forward_now(&buzzer_dev->mytimer, buzzer_dev->kt);

} else {
gpio_set_value(BUZZER_IO, 1);

buzzer_dev->kt = ktime_set(0, 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,0,1,BUZZER_DEVICE_NAME);
if(ret != 0){
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,1);

//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,1);

init_waitqueue_head(&buzzer_dev->wait_queue);

#if BUZZER_GPIO_SWITCH
//初始化Buzzer的GPIO
ret = buzzer_gpio_init();
if(ret !=0){
prdebug("error buzzer_gpio_init");
goto err_device_create;
}

#endif

return 0;

#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,1);

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,1);
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-4.5.1-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_5.1/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 = -1;
unsigned long  on = -1;

fd = open("/dev/buzzer-1",O_RDWR);
if(fd < 0){
perror("open");
exit(1);
}

on = atol(argv[1]);
write(fd,&on,4);

close(fd);

return 0;
}

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。