Explanation of Android Vibrator System

Platform MTK6573

Android Vibrator System Architecture

I. Driver Layer

Modify and add Linux kernel files for Android

/kernel/drivers/staging/android/timed_output.h/kernel/drivers/staging/android/timed_output.c

Timed_output.h defines the timed_output_dev struct.

 
 

  
  
struct timed_output_dev { 
  
  
    const char  *name; 
  
  
 
  
  
    /* enable the output and set the timer */ 
  
  
    void    (*enable)(struct timed_output_dev *sdev, int timeout); 
  
  
 
  
  
    /* returns the current number of milliseconds remaining on the timer */ 
  
  
    int     (*get_time)(struct timed_output_dev *sdev); 
  
  
 
  
  
    /* private data */ 
  
  
    struct device   *dev; 
  
  
    int     index; 
  
  
    int     state; 
  
  
}; 
 
 

Timed_output.c implements this struct. The timed_output_dev_register function is used for registration and timed_output_dev_unregister is used for cancellation.

 
 

  
  
int timed_output_dev_register(struct timed_output_dev *tdev) 
  
  
{ 
  
  
    int ret; 
  
  
 
  
  
    if (!tdev || !tdev->name || !tdev->enable || !tdev->get_time) 
  
  
        return -EINVAL; 
  
  
 
  
  
    ret = create_timed_output_class(); 
  
  
    if (ret < 0) 
  
  
        return ret; 
  
  
 
  
  
    tdev->index = atomic_inc_return(&device_count); 
  
  
    tdev->dev = device_create(timed_output_class, NULL, 
  
  
        MKDEV(0, tdev->index), NULL, tdev->name); 
  
  
    if (IS_ERR(tdev->dev)) 
  
  
        return PTR_ERR(tdev->dev); 
  
  
 
  
  
    ret = device_create_file(tdev->dev, &dev_attr_enable); 
  
  
    if (ret < 0) 
  
  
        goto err_create_file; 
  
  
 
  
  
    dev_set_drvdata(tdev->dev, tdev); 
  
  
    tdev->state = 0; 
  
  
    return 0; 
  
  
 
  
  
err_create_file: 
  
  
    device_destroy(timed_output_class, MKDEV(0, tdev->index)); 
  
  
    printk(KERN_ERR "timed_output: Failed to register driver %s\n", 
  
  
            tdev->name); 
  
  
 
  
  
    return ret; 
  
  
} 
  
  
EXPORT_SYMBOL_GPL(timed_output_dev_register); 
  
  
 
  
  
void timed_output_dev_unregister(struct timed_output_dev *tdev) 
  
  
{ 
  
  
    device_remove_file(tdev->dev, &dev_attr_enable); 
  
  
    device_destroy(timed_output_class, MKDEV(0, tdev->index)); 
  
  
    dev_set_drvdata(tdev->dev, NULL); 
  
  
} 
  
  
EXPORT_SYMBOL_GPL(timed_output_dev_unregister); 
 
 

Driver implementation porting

Take MTK 6573 as an Example

./Mediatek/platform/mt6573/kernel/drivers/vibrator. c

Operation Device

First open the mobile phone debugging, connect to the USB, execute the adb shell, and enter/sys/devices/timed_output/vibrator/

Execute echo "10000" enable to find that the mobile phone is shaking

 
 

  
  
# echo "10000" enable 
  
  
echo "10000" enable 
  
  
10000 enable 
 
 

Run cat enable to view the remaining number of current vibration time:

 
 

  
  
# cat enable 
  
  
cat enable 
  
  
0 
 
 

Ii. Hardware Abstraction Layer

Android encapsulates calls to the underlying driver and becomes the hardware abstraction layer.

/Hardware/libhardware_legacy/vibrator. c

 
 

  
  
int vibrator_on(int timeout_ms) 
  
  
{ 
  
  
    /* constant on, up to maximum allowed time */ 
  
  
    return sendit(timeout_ms); 
  
  
} 
  
  
 
  
  
int vibrator_off() 
  
  
{ 
  
  
    return sendit(0); 
  
  
} 
 
 

Iii. JNI framework layer

The Android JNI framework layer facilitates Java to call the C/C ++ method.

./Frameworks/base/services/jni/com_android_server_VibratorService.cpp

 
 

  
  
namespace android 
  
  
 { 
  
  
  
  
  
 static void vibratorOn(JNIEnv *env, jobject clazz, jlong timeout_ms) 
  
  
 { 
  
  
     // LOGI("vibratorOn\n"); 
  
  
     vibrator_on(timeout_ms); 
  
  
 } 
  
  
 static void vibratorOff(JNIEnv *env, jobject clazz) 
  
  
 { 
  
  
     // LOGI("vibratorOff\n"); 
  
  
     vibrator_off(); 
  
  
 } 
  
  
 static JNINativeMethod method_table[] = { 
  
  
     { "vibratorOn", "(J)V", (void*)vibratorOn }, 
  
  
     { "vibratorOff", "()V", (void*)vibratorOff } 
  
  
 }; 
  
  
 int register_android_server_VibratorService(JNIEnv *env) 
  
  
 { 
  
  
     return jniRegisterNativeMethods(env, "com/android/server/VibratorService", 
  
  
             method_table, NELEM(method_table)); 
  
  
 } 
  
  
}; 
 
 

Iv. Java Application Layer

This layer includes Java application calls and Android system service Java Layer

./Frameworks/base/services/java/com/android/server/VibratorService. java