关键词： 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：/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
1 #include2 #include 3 #include 4 #include 5 #include 6 #include 7 #include 8 #include 9 #include 10 #include 11 #include 12 #include 13 #include 14 15 #include 16 #include 17 18 #include 19 20 #define BUZZER_DEVICE_NAME "mybuzzer" 21 #define BUZZER_CLASS_NAME "mybuzzer" //sys/class/mybuzzer 22 #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 23 24 25 #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 26 #define BUZZER_DELAY_TIME_HIGHT (190000) //2.7KHZ 27 #define BUZZER_DELAY_TIME_LOW (190000) //2.7KHZ 28 #define DE_BUG 1 29 30 #if DE_BUG 31 #define prdebug(fmt,arg...) printk("zbzhuang"KERN_ERR fmt"\n",##arg) 32 #else 33 #define prdebug(fmt,arg...) do{}while(0); 34 #endif 35 36 37 38 typedef enum { 39 BUZZER_DISABLE = 0, 40 BUZZER_ENABLE, 41 }BUZZER_STATUS_t; 42 43 //buzzer的设备对象 44 struct buzzer_chip{ 45 dev_t devno; 46 struct cdev *cdev; 47 struct class *cls; 48 struct device *dev; 49 unsigned long count; //从应用空间读取的数据 50 struct semaphore sem; 51 struct hrtimer mytimer; 52 ktime_t kt; //设置定时时间 53 wait_queue_head_t wait_queue; 54 BUZZER_STATUS_t status; 55 }; 56 57 58 59 60 static int count = 1000; 61 struct buzzer_chip *buzzer_dev; 62 63 static void buzzer_test(void); 64 static void buzzer_gpio_start(void); 65 static enum hrtimer_restart hrtimer_handler(struct hrtimer *timer); 66 67 68 int buzzer_drv_open (struct inode * inode, struct file *filp) 69 { 70 int minor; 71 int major; 72 73 74 prdebug("--------------%s----------------",__func__); 75 76 minor = iminor(inode); 77 major = imajor(inode); 78 79 prdebug("\r\nmajor = %d minor = %d\rn",major,minor); 80 filp->private_data = (void *)minor; 81 82 if(down_interruptible(&buzzer_dev->sem)) 83 return -ERESTARTSYS; 84 85 return 0; 86 } 87 ssize_t buzzer_drv_read (struct file *filp, char __user *userbuf, size_t count, loff_t *fpos) 88 { 89 int ret; 90 91 prdebug("--------------%s----------------",__func__); 92 93 if(filp->f_flags & O_NONBLOCK){ 94 return -EAGAIN; 95 } 96 97 ret = copy_to_user(userbuf,&buzzer_dev->count,count); 98 if(ret > 0){ 99 prdebug("error copy_to_user");100 return -EFAULT;101 }102 prdebug("%s :read count = %ld",__func__,buzzer_dev->count);103 104 return count;105 }106 ssize_t buzzer_drv_write (struct file *filp, const char __user *userbuf, size_t count, loff_t *fpos)107 {108 int ret;109 110 prdebug("--------------%s----------------",__func__);111 prdebug("task pid[%d] context[%s]",current->pid,current->comm);112 113 ret = copy_from_user(&buzzer_dev->count,userbuf,count);114 if(ret > 0){115 prdebug("error copy_from_user");116 return -EFAULT;117 }118 119 prdebug("%s :write count = %ld",__func__,buzzer_dev->count);120 121 122 123 124 if(buzzer_dev->count){125 if(buzzer_dev->status == BUZZER_DISABLE){126 //启动定时器 127 prdebug("-----------start hrtimer timer-------------");128 buzzer_dev->status = BUZZER_ENABLE;129 buzzer_gpio_start();130 wait_event(buzzer_dev->wait_queue, buzzer_dev->status == BUZZER_DISABLE);131 prdebug("------------wake up queue-------------------------------");132 }else{133 prdebug("buzzer_aready work");134 }135 136 }else{137 138 }139 140 141 return count;142 143 }144 int buzzer_drv_close (struct inode *inode, struct file *filp)145 {146 147 prdebug("--------------%s----------------",__func__);148 up(&buzzer_dev->sem);149 150 return 0;151 152 }153 154 const struct file_operations buzzer_fops = {155 .open = buzzer_drv_open,156 .write = buzzer_drv_write,157 .read = buzzer_drv_read,158 .release = buzzer_drv_close,159 160 };161 162 static int buzzer_gpio_init(void)163 {164 int ret = -1;165 166 if(gpio_request(BUZZER_IO, "BUZZER_GPIO")){167 prdebug("error buzzer_gpio_init");168 return ret;169 170 }else{171 gpio_direction_output(BUZZER_IO, 1);172 gpio_set_value(BUZZER_IO, 1);173 buzzer_dev->status = BUZZER_DISABLE;174 }175 176 return 0;177 178 }179 180 static void buzzer_gpio_exit(void)181 {182 gpio_set_value(BUZZER_IO, 1);183 gpio_free(BUZZER_IO);184 }185 186 static void buzzer_gpio_start(void)187 {188 prdebug("-----------buzzer_gpio_start------------");189 190 191 192 //高精度定时器193 hrtimer_init(&buzzer_dev->mytimer,CLOCK_MONOTONIC,HRTIMER_MODE_REL);194 buzzer_dev->mytimer.function = hrtimer_handler;195 buzzer_dev->kt = ktime_set(0, BUZZER_DELAY_TIME_LOW);196 hrtimer_start(&buzzer_dev->mytimer,buzzer_dev->kt,HRTIMER_MODE_REL);197 198 199 200 }201 202 static void buzzer_test(void)203 {204 unsigned long i;205 206 prdebug("-----------start test buzzer------------");207 for(i = 0;i < 10000;i ++){208 gpio_set_value(BUZZER_IO, 0);209 udelay(150);210 gpio_set_value(BUZZER_IO, 1);211 udelay(150);212 }213 prdebug("-----------end test buzzer------------");214 }215 216 static enum hrtimer_restart hrtimer_handler(struct hrtimer *timer)217 {218 219 220 //prdebug("--------------%s----------------",__func__);221 222 if(buzzer_dev->count != 1){223 224 if (gpio_get_value(BUZZER_IO) == 1) {225 gpio_set_value(BUZZER_IO, 0);226 227 buzzer_dev->kt = ktime_set(0, BUZZER_DELAY_TIME_LOW);228 hrtimer_forward_now(&buzzer_dev->mytimer, buzzer_dev->kt);229 230 } else {231 gpio_set_value(BUZZER_IO, 1);232 233 buzzer_dev->kt = ktime_set(0, BUZZER_DELAY_TIME_HIGHT);234 hrtimer_forward_now(&buzzer_dev->mytimer, buzzer_dev->kt);235 }236 buzzer_dev->count --;237 return HRTIMER_RESTART;238 }else{239 buzzer_dev->count --;240 buzzer_dev->status = BUZZER_DISABLE;241 prdebug("buzzer_dev->count = %d",buzzer_dev->count);242 prdebug("-----------finsh hrtimer timer-------------");243 wake_up(&buzzer_dev->wait_queue);244 return HRTIMER_NORESTART;245 }246 247 248 }249 250 251 static int __init buzzer_drv_init(void)252 {253 int ret;254 255 256 prdebug("--------------%s----------------",__func__);257 258 buzzer_dev = kzalloc(sizeof(struct buzzer_chip),GFP_KERNEL);259 if(buzzer_dev == NULL){260 prdebug("kzalloc error");261 return -ENOMEM;262 }263 264 //动态的申请设备号265 ret = alloc_chrdev_region(&buzzer_dev->devno,0,1,BUZZER_DEVICE_NAME);266 if(ret != 0){267 prdebug("error alloc_chrdev_region");268 goto err_free;269 }270 271 //分配cdev对象272 buzzer_dev->cdev = cdev_alloc();273 cdev_init(buzzer_dev->cdev,&buzzer_fops);274 cdev_add(buzzer_dev->cdev,buzzer_dev->devno,1);275 276 //自动创建设备节点277 buzzer_dev->cls = class_create(THIS_MODULE,BUZZER_CLASS_NAME);278 if(IS_ERR(buzzer_dev->cls)){279 prdebug("error class_create");280 ret = PTR_ERR(buzzer_dev->cls);281 goto err_unregister;282 }283 284 buzzer_dev->dev = device_create(buzzer_dev->cls,NULL,buzzer_dev->devno,NULL,"buzzer-%d",BUZZER_DEVICE_NUM);285 if(IS_ERR(buzzer_dev->dev)){286 prdebug("error device_create");287 ret = PTR_ERR(buzzer_dev);288 goto err_class_error;289 }290 291 //信号量292 sema_init(&buzzer_dev->sem,1);293 294 init_waitqueue_head(&buzzer_dev->wait_queue);295 296 297 298 299 300 #if BUZZER_GPIO_SWITCH301 //初始化Buzzer的GPIO302 ret = buzzer_gpio_init();303 if(ret !=0){304 prdebug("error buzzer_gpio_init");305 goto err_device_create;306 }307 308 #endif309 310 311 312 return 0;313 314 #if BUZZER_GPIO_SWITCH315 err_device_create:316 device_destroy(buzzer_dev->cls,buzzer_dev->devno);317 #endif318 319 err_class_error:320 class_destroy(buzzer_dev->cls);321 322 err_unregister: 323 cdev_del(buzzer_dev->cdev);324 unregister_chrdev_region(buzzer_dev->devno,1);325 326 err_free:327 kfree(buzzer_dev);328 return ret;329 330 331 }332 333 static void __exit buzzer_drv_exit(void)334 {335 prdebug("--------------%s----------------",__func__);336 #if BUZZER_GPIO_SWITCH337 buzzer_gpio_exit();338 #endif339 device_destroy(buzzer_dev->cls,buzzer_dev->devno);340 class_destroy(buzzer_dev->cls);341 cdev_del(buzzer_dev->cdev);342 unregister_chrdev_region(buzzer_dev->devno,1);343 kfree(buzzer_dev);344 345 }346 347 module_init(buzzer_drv_init);348 module_exit(buzzer_drv_exit);349 MODULE_LICENSE("GPL");350 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_appMODULE_NAME = buzzer_driver#内核源码路径#KERNEL_DIR = /home/zsf/rk3188_5.1/android/kernelKERNEL_DIR = /home/zsf/u4209/s5p4418-5.1-android/trunk/kernelCUR_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#include #include #include #include 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
1 LOCAL_PATH := $(call my-dir) 2 3 include $(CLEAR_VARS) 4 5 LOCAL_MODULE_TAGS := optional 6 7 LOCAL_MODULE := buzzer_write 8 9 LOCAL_SRC_FILES := buzzer_write.cpp10 11 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。