android系统开发(七)-背光模块

 

1,总论
背光模块属于HAL层开发,HAL层开发,用一句话来概括就是定义一个hardware.h中定义的名称为宏HAL_MODULE_INFO_SYM的hw_module_t结构体,
然后实现结构体的相关内容

2,驱动方面的准备
简单的嵌入式linux驱动,编写LCD背光驱动,并提供接口给上层修改,我所用的是直接修改接口文件,接口如下:
/sys/class/backlight/pwm-backlight/brightness  这个是亮度调节
/sys/class/backlight/pwm-backlight/max_brightness 这个是最大亮度,按照android系统的要求应该设置成255
控制亮度直接写brightness文件即可
背光驱动主要是通过PWM来完成,这里不详细说明。

3,需要包含的头文件
/hardware/libhardware/include/hardware目录下的hardware.h和lights.h
其中hardware.h中定义了通用硬件模块,lights.h中定义了背光设备相关的内容

4,android已有的硬件模块在/hardware/libhardware/modules目录下,为了区分,我们开发的背光模块放置在如下的目录:
vendor/ardent/merlin/lights目录下,编译成lights.default.so放置到/system/lib/hw目录下,模块命名规则可以
参考上一节的内容。

5,修改vendor/ardent/merlin目录下AndroidBoard.mk文件,添加如下内容:
include $(LOCAL_PATH)/lights/Mdroid.mk

6,lights目录新建Mdroid.mk文件,内容如下:
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
LOCAL_SRC_FILES:= lights.c

LOCAL_SHARED_LIBRARIES := /
    libutils /
    libcutils /
    libhardware

LOCAL_PRELINK_MODULE := false

LOCAL_MODULE := lights.default

include $(BUILD_SHARED_LIBRARY)

7,lights目录下新建一个lights.c文件,如下:
const struct hw_module_t HAL_MODULE_INFO_SYM = {
    .tag = HARDWARE_MODULE_TAG,
    .version_major = 1,
    .version_minor = 0,
    .id = LIGHTS_HARDWARE_MODULE_ID,
    .name = "lights module",
    .author = "allen",
    .methods = NULL,
};

8,上面的内容可以直接编译通过,但是因为我将其methods部分指向了空指针,因此没有任何功能,下面来实现此部分
hw_module_t机构体的methods成员是一个指向hw_module_methods_t结构体的一个指针,hw_module_methods_t结构体定义如下:
typedef struct hw_module_methods_t {
    int (*open)(const struct hw_module_t* module, const char* id,struct hw_device_t** device);
} hw_module_methods_t;
据此我们定义一个hw_module_methods_t类型的参数lights_module_methods如下:
struct hw_module_methods_t lights_module_methods = {
    .open = lights_device_open
};
然后将上面的methods由NULL改成lights_module_methods

9,接下来就是定义lights_device_open函数了,此函数的参数和返回值由hw_module_methods_t结构体的open成员决定,此函数定义如下:
static int lights_device_open(const struct hw_module_t *module,const char *id, struct hw_device_t **device)
从lights_device_open函数的参数来看,第一个参数和第二个参数是常量,第三个参数是 一个指向hw_device_t结构体的指针,因此可以断定
实现此函数也就是要完成第三个参数的内容,详细的内容我们可以参考直接调用该函数的内容,在frameworks/base/services/jni目录下的
com_android_server_LightsService.cpp文件中,内容如下:
static light_device_t* get_device(hw_module_t* module, char const* name)
{
    int err;
    hw_device_t* device;
    err = module->methods->open(module, name, &device);
    if (err == 0) {
        return (light_device_t*)device;//device由hw_device_t指针强制转换成light_device_t指针
    } else {
        return NULL;
    }
}

static jint init_native(JNIEnv *env, jobject clazz)
{
    int err;
    hw_module_t* module;
    Devices* devices;
   
    devices = (Devices*)malloc(sizeof(Devices));

    err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
    if (err == 0) {
        devices->lights[LIGHT_INDEX_BACKLIGHT]
                = get_device(module, LIGHT_ID_BACKLIGHT);
        devices->lights[LIGHT_INDEX_KEYBOARD]
                = get_device(module, LIGHT_ID_KEYBOARD);
        devices->lights[LIGHT_INDEX_BUTTONS]
                = get_device(module, LIGHT_ID_BUTTONS);
        devices->lights[LIGHT_INDEX_BATTERY]
                = get_device(module, LIGHT_ID_BATTERY);
        devices->lights[LIGHT_INDEX_NOTIFICATIONS]
                = get_device(module, LIGHT_ID_NOTIFICATIONS);
        devices->lights[LIGHT_INDEX_ATTENTION]
                = get_device(module, LIGHT_ID_ATTENTION);
        devices->lights[LIGHT_INDEX_BLUETOOTH]
                = get_device(module, LIGHT_ID_BLUETOOTH);
        devices->lights[LIGHT_INDEX_WIFI]
                = get_device(module, LIGHT_ID_WIFI);
    } else {
        memset(devices, 0, sizeof(Devices));
    }

    return (jint)devices;
}
从上面的内容我们可以看出lights_device_open的第一个参数是JNI层用hw_get_module所获得,第二个参数根据设备的不同有很多种情况
该参数的内容定义在lights.h中,全部情况如下:
#define LIGHT_ID_BACKLIGHT          "backlight"
#define LIGHT_ID_KEYBOARD           "keyboard"
#define LIGHT_ID_BUTTONS            "buttons"
#define LIGHT_ID_BATTERY            "battery"
#define LIGHT_ID_NOTIFICATIONS      "notifications"
#define LIGHT_ID_ATTENTION          "attention"
#define LIGHT_ID_BLUETOOTH          "bluetooth"
#define LIGHT_ID_WIFI               "wifi"
lights调节有背光,键盘,按键,电池,通知,提醒,蓝牙和WIF
第三个参数是一个指向一个hw_device_t的指针,但是com_android_server_LightsService.cpp文件中的背光调节函数定义如下:
static void setLight_native(JNIEnv *env, jobject clazz, int ptr,
        int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)
{
    Devices* devices = (Devices*)ptr;
    light_state_t state;

    if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {
        return ;
    }

    memset(&state, 0, sizeof(light_state_t));
    state.color = colorARGB;
    state.flashMode = flashMode;
    state.flashOnMS = onMS;
    state.flashOffMS = offMS;
    state.brightnessMode = brightnessMode;

    devices->lights[light]->set_light(devices->lights[light], &state);
}
get_device函数中将hw_device_t指针强制转换成light_device_t指针给调节背光用,而light_device_t定义如下:
struct light_device_t {
    struct hw_device_t common;
    int (*set_light)(struct light_device_t* dev,
            struct light_state_t const* state);
};
因此在实现lights_device_open的第三个参数的时候,我们应该定义一个light_device_t类型结构体,然后
将起common域的指针地址传递过去。这样虽然传递的是一个hw_device_t指针地址,但是JNI层可以将其强制转换
成light_device_t指针地址用,否则devices->lights[light]->set_light就会起不到作用了。实现如下:
static int lights_device_open(const struct hw_module_t *module,const char *id, struct hw_device_t **device)
{
    struct light_device_t *dev = NULL;
    int resvalue = -1;
    dev = calloc(sizeof(struct light_device_t),1);
    dev->common.tag = HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = (struct hw_module_t *)module;
    dev->common.close = lights_device_close;
    if(!strcmp(id, LIGHT_ID_BACKLIGHT))
    {
        dev->set_light = lcd_set_light;
        resvalue = 0;
    }
    else
    {
        dev->set_light = other_set_light;
        resvalue = 0;
    }
    *device = &dev->common;
    return resvalue;
}

10,实现lights_device_close,lcd_set_light和other_set_light,这个主要是调用驱动提供的接口直接控制硬件,举例如下:
static int lights_device_close(struct hw_device_t* device)
{
    struct light_device_t *m_device = (struct light_device_t *)device;
    if(m_device)
        free(m_device);
    return 0;
}
static int lcd_set_light(struct light_device_t* dev,struct light_state_t const* state)
{
    int fd = -1;
    int bytes = 0;
    int rlt = -1;
    unsigned char brightness = ((77*((state->color>>16)&0x00ff))
                               + (150*((state->color>>8)&0x00ff))
                               + (29*(state->color&0x00ff))) >> 8;
    fd = open("/sys/class/backlight/pwm-backlight/brightness", O_RDWR);
    if(fd>0)
    {
        char buffer[20];
     memset(buffer, 0, 20);
    bytes = sprintf(buffer, "%d", brightness);
    rlt = write(fd, buffer, bytes);
        if(rlt>0)
        {
           close(fd);
           return 0;
        }
    }
    close(fd);
    return -1;
}

static int other_set_light(struct light_device_t* dev,struct light_state_t const* state)
{
    return 0;
}

11,因为上面调节背光是通过写/sys/class/backlight/pwm-backlight/brightness文件来完成,因此一定要设置该文件的权限,
在init.xxx.rc文件中添加如下的内容:
    # for control LCD backlight
    chown system system /sys/class/backlight/pwm-backlight/brightness
    chmod 0666 /sys/class/backlight/pwm-backlight/brightness

12,修改完成后经验证亮度调节可用,上面的例子只是实现了lights部分功能,如果需要完成所有的功能,请参考hardware.h, lights.h和com_android_server_LightsService.cpp文件中的内容。

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