Android模拟器学framework和driver之battery & backlight-----6. backlight in hal

这里我们来介绍下backlight hal层，和之前一样，跟之前我们介绍的temperature的hal差不多，比sensor的hal还简单，这里我就不多说hal的介绍了，之前都有介绍的比较详细了，不清楚的可以参考前面的文章：

http://blog.csdn.net/zhangjie201412/article/details/7225617

首先要明确我们的目标，这里主要是封装一些方法，然后给android framework层使用（jni layer），打开一个sysfs中的节点，然后read/write，

明白这点就够了，直接贴代码：

/hardware/libhardware/module/lights/android_light.c

#define LOG_TAG "light"#include <hardware/lights.h>#include <fcntl.h>#include <errno.h>#include <stdlib.h>#include <cutils/log.h>#include <cutils/atomic.h>#include <cutils/properties.h>#define MAX_BRIGHTNESS255#define DEF_BACKLIGHT_DEV"android-backlight"#define DEF_BACKLIGHT_PATH"/sys/class/backlight/"/***************************************************************/struct lights_module_t{struct hw_module_t common;};static int lights_device_open(const struct hw_module_t* module,const char* name,struct hw_device_t** device);static struct hw_module_methods_t lights_module_methods = {.open=lights_device_open};const struct lights_module_t HAL_MODULE_INFO_SYM = {    .common= {        .tag= HARDWARE_MODULE_TAG,        .version_major= 1,        .version_minor= 0,        .id= LIGHTS_HARDWARE_MODULE_ID,        .name= "Lights module",        .author= "Freescale Semiconductor",        .methods= &lights_module_methods,    }};static char max_path[256], path[256];// ****************************************************************************// module// ****************************************************************************static int set_light_backlight(struct light_device_t* dev,                               struct light_state_t const* state){    int result = -1;    unsigned int color = state->color;    unsigned int brightness = 0, max_brightness = 0;    FILE *file;    brightness = ((77*((color>>16)&0x00ff)) + (150*((color>>8)&0x00ff)) +                 (29*(color&0x00ff))) >> 8;    LOGV("set_light, get brightness=%d", brightness);    file = fopen(max_path, "r");    if (!file) {        LOGE("can not open file %s\n", max_path);return result;    }    fread(&max_brightness, 1, 3, file);    fclose(file);    max_brightness = atoi((char *) &max_brightness);    brightness = brightness * max_brightness / MAX_BRIGHTNESS;    LOGV("set_light, max_brightness=%d, target brightness=%d",        max_brightness, brightness);    file = fopen(path, "w");    if (!file) {        LOGE("can not open file %s\n", path);        return result;    }    fprintf(file, "%d", brightness);    fclose(file);    result = 0;    return result;}static int light_close_backlight(struct hw_device_t *dev){    struct light_device_t *device = (struct light_device_t*)dev;    if (device)        free(device);    return 0;}/*****************************************************************************/static int lights_device_open(const struct hw_module_t* module,                              const char* name, struct hw_device_t** device){    int status = -EINVAL;    LOGV("lights_device_open\n");    if (!strcmp(name, LIGHT_ID_BACKLIGHT)) {        struct light_device_t *dev;        char value[PROPERTY_VALUE_MAX];        dev = malloc(sizeof(*dev));        /* initialize our state here */        memset(dev, 0, sizeof(*dev));        /* initialize the procs */        dev->common.tag = HARDWARE_DEVICE_TAG;        dev->common.version = 0;        dev->common.module = (struct hw_module_t*) module;        dev->common.close = light_close_backlight;        dev->set_light = set_light_backlight;*device = &dev->common;//        property_get("hw.backlight.dev", value, DEF_BACKLIGHT_DEV);//        strcpy(path, DEF_BACKLIGHT_PATH);//        strcat(path, value);//        strcpy(max_path, path);//        strcat(max_path, "/max_brightness");//        strcat(path, "/brightness");strcpy(path, "/sys/devices/platform/android-backlight.0/backlight/android-backlight.0/brightness");strcpy(max_path, "/sys/devices/platform/android-backlight.0/backlight/android-backlight.0/max_brightness");LOGI("max backlight file is %s\n", max_path);        LOGI("backlight brightness file is %s\n", path);        status = 0;    }    /* todo other lights device init */    return status;}

接下来是android.mk

LOCAL_PATH := $(call my-dir)# HAL module implemenation, not prelinked and stored in hw/include $(CLEAR_VARS)LOCAL_MODULE_TAGS := optionalLOCAL_PRELINK_MODULE := falseLOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hwLOCAL_SHARED_LIBRARIES := liblog libcutilsLOCAL_SRC_FILES := android_light.cLOCAL_MODULE := lights.default#LOCAL_MODULE_TAGS := enginclude $(BUILD_SHARED_LIBRARY)

这里我要声明的是，在读写之前先把文件的权限打开，在init.rc中去做

#add by Jay    chmod 777 /sys/bus/iio/devices/device0/lux    chmod 777 /sys/bus/iio/devices/device1/value    chmod 777 /sys/bus/iio/devices/device1/active    chmod 777 /sys/class/backlight/android-backlight.0/brightness    chmod 777 /sys/class/backlight/android-backlight.0/max_brightness

好了，hal层我们就添加到这边，我们来重新编译，然后打开我们的模拟器，

打开setting中的display，然后调节屏幕亮度，然后再cat brightness会发现节点中的值改变了

把亮度调到最高，值变成了255.

结束！！！！下面会分析android framework中jni去实现lightService。