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。
本文来自CSDN博客,转载请标明出处:http://blog.csdn.net/jiajie961/archive/2010/11/23/6030405.aspx