在android车机上调试USB Camera录像拍照功能

USB Camera在上一篇文章中已经跑起来了，上次的情况是camera预览可以，拍照、录像不行。除了强制设置视频设备设备文件为/dev/video2，也就是这个usb camera插入系统后自动分配的设备文件，其他没有修改。一拍照或者录像，程序就死了，错误打印如下：

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01-01 09:33:59.490 V/CAM_FocusManager( 2990): Start autofocus.

01-01 09:33:59.580 V/CAM_PhotoModule( 2990): mAutoFocusTime = 87ms

01-01 09:33:59.650 V/CAM_PhotoModule( 2990): onShutterButtonClic[ 263.837941] uvcvideo: Trying format 0x56595559 (YUYV): 960x720.

[ 263.837964] uvcvideo: Using default frame interval 66666.6 us (15.0 fps).

k: mCameraState=1

01-01 09:33:59.650 D/V4L2CameraDevice( 1077): in V4L2Camera::TryFmtSize: w: 960, h: 720

01-01 09:33:59.700 D/V4L2CameraDevice( 1077): out V4L2Camera::TryFmtSize: w: 960, h: 720

[ 263.897491] uvcvideo: Trying format 0x56595559 (YUYV): 640x480.

01-01 09:33:59.710 D/V4L2CameraDevice( 1077): in V4L2Camera::Try[ 263.904745] uvcvideo: Using default frame interval 33333.3 us (30.0 fps).

FmtSize: w: 640, h: 480

01-01 09:33:59.750 D/V4L2CameraDevice( 1077): out V4L2Camera::TryFmtSize: w: 640, h: 480

[ 264.008038] Binder_2 used greatest stack depth: 5032 bytes left

01-01 09:33:59.870 D/CameraHardware( 1077): Starting camera for [ 264.056815] uvcvideo: Setting frame interval to 1/30 (333333).

picture: NV12(jpeg)[640x480]

01-01 09:33:59.870 D/V4L2CameraDevice( 1077): startDevice, wxh: 640x480, fmt: 0x3231564e

[ 264.101826] fuction=uvc_v4l2_do_ioctl, line=793

01-01 09:33:59.910 D/V4L2CameraDevice( 1077): v4l2SetVideoParams[ 264.106430] fuction=uvc_v4l2_set_format, line=300

, line: 903, w: 640, h: 480, pfmt: 0x3231564e

01-01 09:33:59.91[ 264.116702] fuction=uvc_v4l2_set_format, line=304

0 D/V4L2CameraDevice( 1077): v4l2SetVideoParams, line: 919, mCap[ 264.126906] uvcvideo: Trying format 0x56595559 (YUYV): 640x480.

tureFormat: 0x56595559, format.fmt.pix.pixelformat: 0X56595559, [ 264.138377] uvcvideo: Using default frame interval 33333.3 us (30.0 fps).

V4L2_PIX_FMT_YUYV: 0x56595559

[ 264.173788] uvcvideo: Setting frame interval to 1/15 (666666).

01-01 09:33:59.990 E/V4L2CameraDevice( 1077): VIDIOC_S_FMT Failed: Device or resource busy

[ 264.227065] uvcvideo: uvc_v4l2_mmap

01-01 09:34:00.040 E/sunxi_alloc( 1077): can not alloc size 0

[ 264.247304] uvcvideo: Device requested 3072 B/frame bandwidth.

[ 264.247322] uvcvideo: Selecting alternate setting 6 (3072 B/frame bandwidth).

[ 264.251846] uvcvideo: Allocated 5 URB buffers of 32x3072 bytes each.

01-01 09:34:00.080 W/V4L2CameraDevice( 1077): preview thread dose not started

01-01 09:34:00.170 W/V4L2CameraDevice( 1077): preview thread dose not started

01-01 09:34:00.270 W/V4L2CameraDevice( 1077): preview thread dose not started

01-01 09:34:00.380 W/V4L2CameraDevice( 1077): preview thread dose not started

01-01 09:34:00.480 W/V4L2CameraDevice( 1077): preview thread dose not started

01-01 09:34:00.580 W/V4L2CameraDevice( 1077): preview thread dose not started

跟了一下uvc的driver，头很大，代码一大堆，千丝万缕中找到错误出在uvc_v4l2_set_format函数里。又加了一些打印发现错误出在：

if (uvc_queue_allocated(&stream->queue)) {

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

ret = -EBUSY;

goto done;

}

看了一下uvc_queue_allocated这个接口，发现里面是判断这个queue的buffer size是否大于0，大于0的话就说明已经分配过了，调用uvc_queue_allocated这个接口就会返回true，从而出错出去，会造成camera hal层接着出错。

因为在android camera apk应用中一进去就是preview的状态，切到录像或者拍照要另外执行动作，整个处理会有变化，然而可能是因为UVC的设备打开后操作产生的stream的queue没有释放，造成在重现uvc_v4l2_set_format的时候，就会在中间出错跳出，所以笔者稍作了一下改动，在调用uvc_queue_allocated返回出错的地方屏蔽掉，也就是你有这个queue，我就继续用你，理论上应该是可行。重新编译一下，烧进去，一跑，果然可以拍照跟录像了。但是拍的照片有一点小问题，就是在照片中莫名的多了一些短的黑线，预览的时候没有这些短线，笔者还不知道是什么原因。另外笔者还需要研究的是多个usb camera在android中看看是否能同时工作，预计这里面有很多工作，还是继续朝着这个方向前进。下面贴修改的代码以及排的一张照片：

static int uvc_v4l2_set_format(struct uvc_streaming *stream,

struct v4l2_format *fmt)

{

struct uvc_streaming_control probe;

struct uvc_format *format;

struct uvc_frame *frame;

int ret;

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

if (fmt->type != stream->type)

return -EINVAL;

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

ret = uvc_v4l2_try_format(stream, fmt, &probe, &format, &frame);

if (ret < 0)

return ret;

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

mutex_lock(&stream->mutex);

if (uvc_queue_allocated(&stream->queue)) {

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

//ret = -EBUSY;

//goto done;}

memcpy(&stream->ctrl, &probe, sizeof probe);

stream->cur_format = format;

stream->cur_frame = frame;

printk("fuction=%s, line=%d\n",__FUNCTION__, __LINE__);

done:

mutex_unlock(&stream->mutex);

return ret;

}