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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。转载地址:http://ngfsi.baihongyu.com/