Vibrator function support in Android

Android application connect to HAL by JNI interface, for vibrator, the JNI interface is defined very simple.


JNI: frameworks/base/services/jni/com_android_server_VibratorService.cpp


static jboolean vibratorExists(JNIEnv *env, jobject clazz)
{
    return vibrator_exists() > 0 ? JNI_TRUE : JNI_FALSE;
}


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[] = {
{ "vibratorExists", "()Z", (void*)vibratorExists },
{ "vibratorOn", "(J)V", (void*)vibratorOn },
{ "vibratorOff", "()V", (void*)vibratorOff }
};

vibratorOn, vibratorOff and vibratorExists just simple wrapper of vibrator_on, vibrator_off and vibrator_exists, which is provide by device maker, through HAL interface.

HAL: hardware/libhardware_legacy/vibrator/vibrator.c


#define THE_DEVICE "/sys/class/timed_output/vibrator/enable"


int vibrator_exists()
{
    int fd;


#ifdef QEMU_HARDWARE
    if (qemu_check()) {
        return 1;
    }
#endif


    fd = open(THE_DEVICE, O_RDWR);
    if(fd < 0)
        return 0;
    close(fd);
    return 1;
}



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


int vibrator_off()
{
    return sendit(0);
}

HAL call into kernel space by sysfs, path at "/sys/class/timed_output/vibrator/enable"
It's a Android designed feature, a timed_output or timed_gpio device.

If you echo 10000 into this sysfs, then it will vibrate for ten seconds :

$ echo 10000 > /sys/class/timed_output/vibrator/enable 

If you cat it during the vibration, you will saw how many ms before it back to quiet :

$ cat /sys/class/timed_output/vibrator/enable

315

Inside kernel space, Android defined two new platform driver to be use for vibrator : timed_gpio and timed_output.

By grab HC kernel source that released by Acer/ASUS, found that they are using different of implementation.

Acer use a gpio pin, config with a timed_gpio driver, hook up with platform_device driver, and also to timed_output driver to provide vibrator interface from sysfs.

ASUS use an IC max1749, directly register a timed_output interface to provide vibrator interface from sysfs.

PS. Beside kernel source, above source code is trace from AOSP 4.0.1.