心怀浪漫宇宙，也珍惜人间日常。

这篇文章基于高通msm8937/msm8939平台，分下面几点内容展开：

一、主要硬件模块
二、Camera 预览数据流
三、Android Camera 软件架构 
四、HAL层dump Yuv 
五、Jepg Encoder dump YUV

01

主要硬件模块(Major Hardware Blocks Used)

1）Camera Control Interface (CCI)

Used for dedicated I2C for camera subsystem

2）Video Frontend (VFE4)

Image processing hardware for processing camera frame data MSM8939 VFE can support up to 21 MP

VFE4 maximum clock is 320 MHz in Normal mode and 600 MHz in Turbo mode

3）JPEG encoder/decoder

Hardware block for JPEG encoding

JPEG encoder maximum clock is 266 MHz in Normal mode

LIBJPEG software library is used for decoding

4）Camera Postprocessor (CPP)

Supports flip/rotate, denoise, smooth/sharpen, crop, and upscale features for full-size VFE output frames

--------- 我们经常说的翻转、旋转、降噪、裁剪、按比例缩放等操作就是放在cpp中进行出来。

02

Camera 预览数据量

MDP: (支持16bit总线以上LCD) lcd总线接口类型，支持高速刷屏。

03

Sortware Architechture - Android Camera

MCT ：Media Controller

04

HAL层dump Yuv

上面的文档是针对8939平台的，如果在其它平台上，可能有有点差异，具体值以实际代码为准。

我这边是在8937平台上看的调试代码：

persist.vendor.camera.dumpimg

//------ hardware/qcom/camera/QCamera2/HAL3/QCamera3Channel.cpp
void QCamera3Channel::dumpYUV(mm_camera_buf_def_t *frame, cam_dimension_t dim,
        cam_frame_len_offset_t offset, uint8_t dump_type)
{
    char buf[FILENAME_MAX];
    memset(buf, 0, sizeof(buf));
    static int counter = 0;
    char prop[PROPERTY_VALUE_MAX];
    property_get("persist.vendor.camera.dumpimg", prop, "0");
    mYUVDump = (uint32_t)atoi(prop);
    if (mYUVDump & dump_type) {
        mFrmNum = ((mYUVDump & 0xffff0000) >> 16);
        if (mFrmNum == 0) {
            mFrmNum = 10;
        }
        if (mFrmNum > 256) {
            mFrmNum = 256;
        }
        mSkipMode = ((mYUVDump & 0x0000ff00) >> 8);
        if (mSkipMode == 0) {
            mSkipMode = 1;
        }
        if (mDumpSkipCnt == 0) {
            mDumpSkipCnt = 1;
        }
        if (mDumpSkipCnt % mSkipMode == 0) {
            if (mDumpFrmCnt < mFrmNum) {
                /* Note that the image dimension will be the unrotated stream dimension.
                * If you feel that the image would have been rotated during reprocess
                * then swap the dimensions while opening the file
                * */
                switch (dump_type) {
                    case QCAMERA_DUMP_FRM_PREVIEW:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"p_%d_%d_%dx%d.yuv",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    case QCAMERA_DUMP_FRM_VIDEO:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"v_%d_%d_%dx%d.yuv",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    case QCAMERA_DUMP_FRM_INPUT_JPEG:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"s_%d_%d_%dx%d.yuv",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    case QCAMERA_DUMP_FRM_INPUT_REPROCESS:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"ir_%d_%d_%dx%d.yuv",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    case QCAMERA_DUMP_FRM_CALLBACK:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"c_%d_%d_%dx%d.yuv",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    case QCAMERA_DUMP_FRM_OUTPUT_JPEG:
                        snprintf(buf, sizeof(buf), QCAMERA_DUMP_FRM_LOCATION"j_%d_%d_%dx%d.jpg",
                            counter, frame->frame_idx, dim.width, dim.height);
                    break;
                    default :
                        LOGE("dumping not enabled for stream type %d",dump_type);
                    break;
                }
                counter++;
                int file_fd = open(buf, O_RDWR | O_CREAT, 0777);
                ssize_t written_len = 0;
                if (file_fd >= 0) {
                    void *data = NULL;
                    fchmod(file_fd, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
                    if( dump_type == QCAMERA_DUMP_FRM_OUTPUT_JPEG ) {
                        written_len = write(file_fd, frame->buffer, frame->frame_len);
                    }
                    else {
                        for (uint32_t i = 0; i < offset.num_planes; i++) {
                            uint32_t index = offset.mp[i].offset;
                            if (i > 0) {
                                index += offset.mp[i-1].len;
                            }
                            for (int j = 0; j < offset.mp[i].height; j++) {
                                data = (void *)((uint8_t *)frame->buffer + index);
                                written_len += write(file_fd, data,
                                        (size_t)offset.mp[i].width);
                                index += (uint32_t)offset.mp[i].stride;
                            }
                        }
                    }
                    LOGH("written number of bytes %ld\n", written_len);
                    mDumpFrmCnt++;
                    frame->cache_flags |= CPU_HAS_READ;
                    close(file_fd);
                } else {
                    LOGE("failed to open file to dump image");
                }
            }
        } else {
            mDumpSkipCnt++;
        }
    }
}

1）setprop persist.vendor.camera.dumping 4

值设为 1<<2,也就是4，这个dump的是送给Jepg Encode之前的yuv数据。如果需要查看拍照前的yuv数据，可以设置这个进行dump。

2) setprop persist.vendor.camera.dumping 8

值设为 1 << 3 也就是4，可以dump callback的yuv。比如第三方app 的hdr算法，拍照的时候，请求了3张不同ev值的yuv,这时就可以把3张yuv dump出来。

下面是使用第三方app，hdr模式下拍照的dump的例子。