Android Camera HAL V3参数传递

最近一直在调试Android 4.4.3的Camera HAL层，对framework层到HAL的参数传递方法一直不明白，导致调试无从下手，今天总算是有点启发，也不知道对不对，但是要写出来给，一是给自己做个笔记，二是可能会对后来的朋友有些启发；

在调试Camera HAL的过程中发现，HAL层调用的许多framework层的很多回调函数，这点要注意，以前我一直以为都是只能framework向下调用HAL层的函数，而HAL层不能调用到framework层的函数，所以导致我在追踪代码的过程中有很多迷糊的地方；后来知道了这些豁然开朗；

              首先第一个很关键的头文件：myandroid/system/media/camera/include/system/camera_metadata_tags.h，这个头文件中有一个很关键的enum类型camera_metadata_tag；camera_metadata_tag 中很很多tag，每个tag后面的注释部分意思是你要定义一个相应类型的enum或int32[
]类型的数据，并把数据的值注册到系统list中，以后framework和HAL就可以通过tag中的ID匹配相应的参数值；framework层和HAL层通过查找这个tag id找到buffer list中相应的惨值；

typedef enum camera_metadata_tag {
ANDROID_COLOR_CORRECTION_MODE =                   // enum         | public
ANDROID_COLOR_CORRECTION_START,
ANDROID_COLOR_CORRECTION_TRANSFORM,               // rational[]   | public
ANDROID_COLOR_CORRECTION_GAINS,                   // float[]      | public
ANDROID_COLOR_CORRECTION_END,

ANDROID_CONTROL_AE_ANTIBANDING_MODE =             // enum         | public
ANDROID_CONTROL_START,
ANDROID_CONTROL_AE_EXPOSURE_COMPENSATION,         // int32        | public
ANDROID_CONTROL_AE_LOCK,                          // enum         | public
ANDROID_CONTROL_AE_MODE,                          // enum         | public
ANDROID_CONTROL_AE_REGIONS,                       // int32[]      | public<span style="white-space:pre">	</span>//要定义一个public权限的int32[]数据，并把它注册到系统中；
ANDROID_CONTROL_AE_TARGET_FPS_RANGE,              // int32[]      | public
ANDROID_CONTROL_AE_PRECAPTURE_TRIGGER,            // enum         | public
<span style="color:#ff0000;">ANDROID_CONTROL_AF_MODE</span>,                          // enum         | public<span style="white-space:pre">	</span>//自动对焦相关?
ANDROID_CONTROL_AF_REGIONS,                       // int32[]      | public
ANDROID_CONTROL_AF_TRIGGER,
<span style="color:#3333ff;"><strong>ANDROID_CONTROL_AF_AVAILABLE_MODES</strong></span>,               // byte[]       | public<span style="white-space:pre">	</span>//AF控制相关
<span style="color:#ff0000;">ANDROID_FLASH_MODE</span>,                               // enum         | public<span style="white-space:pre">	</span>//闪光灯相关?
//.......................省略部分代码.............................<pre name="code" class="cpp"><span style="font-family: Arial, Helvetica, sans-serif;">ANDROID_BLACK_LEVEL_LOCK =                        // enum         | public</span>

ANDROID_BLACK_LEVEL_START, ANDROID_BLACK_LEVEL_END, //在枚举空间层次结构中的位置。所有供应商的扩展标签必须定义在标签 >=vendor_section_start 后} camera_metadata_tag_t;

上面那些camera_metadata_tag_t中有些enum类型，有些事int32类型，他们具体指什么呢？在myandroid/hardware/imx/mx6/libcamera2/MetadaManager.cpp文件中MetadaManager::createStaticInfo(camera_metadata_t **info, bool sizeRequest)函数中；

status_t MetadaManager::createStaticInfo(camera_metadata_t **info, bool sizeRequest)
{
//.......................................
static const uint8_t <span style="color:#ff0000;">availableAfModes</span>[] = {
ANDROID_CONTROL_AF_MODE_OFF ,				// new add
ANDROID_CONTROL_AF_MODE_AUTO,				// new add
ANDROID_CONTROL_AF_MODE_MACRO,				// new add
//ANDROID_CONTROL_AF_MODE_CONTINUOUS_VIDEO,	// new add
//ANDROID_CONTROL_AF_MODE_CONTINUOUS_PICTURE	// new add
};
//添加对自动对焦模式的支持
ADD_OR_SIZE(<span style="color:#3333ff;"><strong>ANDROID_CONTROL_AF_AVAILABLE_MODES</strong></span>,
<span style="color:#ff0000;">availableAfModes</span>, sizeof(<span style="color:#ff0000;">availableAfModes</span>));
//.......................................
}

Camera HAL层是怎么获得Framework层传下来的参数呢？通过调用myandroid/system/media/camera/src/camera_metadata.c文件中的ANDROID_API接口find_camera_metadata_entry();find_camera_metadata_entry()函数的entry参数是输出指针，得到entry值；entry是一个camera_metadata_entry结构体；通过camera_metadata_entry的union指针传递参数值；

typedef struct camera_metadata_entry {
size_t   index;
uint32_t tag;
uint8_t  type;
size_t   count;
union {
uint8_t *u8;			//trigger
int32_t *i32;			//trigger_id
float   *f;
int64_t *i64;			//timestamp
double  *d;
camera_metadata_rational_t *r;		//帧率相关
} data;
} camera_metadata_entry_t;

myandroid/hardware/imx/mx6/libcamera2/MetadaManager.cpp

status_t MetadaManager::getFrameRate(int *value)
{

camera_metadata_entry_t <span style="color:#ff0000;"><strong>streams</strong></span>;
int res = <span style="color:#3333ff;"><strong>find_camera_metadata_entry</strong></span>(mCurrentRequest,
ANDROID_CONTROL_AE_TARGET_FPS_RANGE, &<span style="color:#ff0000;"><strong>streams</strong></span>);
if (res != NO_ERROR) {
ALOGE("%s: error reading fps range tag", __FUNCTION__);
return BAD_VALUE;
}

int v[2];
for (uint32_t i = 0; i < streams.count && i < 2; i++) {
v[i] = <strong><span style="color:#ff0000;">streams</span></strong>.data.i32[i];<span style="white-space:pre">			</span>//得到framework层的值；
}

if (v[0] > 15 && v[1] > 15) {
*value = 30;
}
else {
*value = 15;
}
return NO_ERROR;
}

framework层是怎么得到HAL层返回的值呢？

myandroid/frameworks/av/services/camera/libcameraservice/device3/Camera3Device.cpp

void Camera3Device::processCaptureResult(const camera3_capture_result *result) {
//.............................................
// Check that there's a timestamp in the result metadata
<span style="white-space:pre">	</span><strong><span style="color:#ff0000;">CameraMetadata </span></strong><span style="color:#3366ff;"><strong>captureResult</strong></span>;<span style="white-space:pre">		</span>//<span style="color: rgb(255, 0, 0); font-weight: bold; font-family: Arial, Helvetica, sans-serif;">CameraMetadata.find(tag)返回</span><span style="color: rgb(51, 102, 255); font-weight: bold; font-family: Arial, Helvetica, sans-serif;">camera_metadata_entry 就得到了HAL层传上来的参数；</span><span style="color: rgb(255, 0, 0); font-weight: bold; font-family: Arial, Helvetica, sans-serif;">
</span>        <strong><span style="color:#3366ff;">camera_metadata_entry </span></strong>entry =
<span style="color:#3333ff;"><strong>captureResult</strong></span>.find(<span style="color:#ff0000;">ANDROID_SENSOR_TIMESTAMP</span>);
if (entry.count == 0) {
SET_ERR("No timestamp provided by HAL for frame %d!",
frameNumber);
gotResult = false;
} else if (timestamp != entry.data.i64[0]) {
SET_ERR("Timestamp mismatch between shutter notify and result"
" metadata for frame %d (%lld vs %lld respectively)",
frameNumber, timestamp, entry.data.i64[0]);
gotResult = false;
}
//.............................................
}

其实myandroid/frameworks/av/include/camera/CameraMetadata.h是framework和HAL参数的中间class；类似个中间变量；以上内容全是个人理解，有错的地方还希望大家指正；一起进步；