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news 2025/7/16 15:42:13

简单查看流程，如有错误请指出。

CameraNativePreview.ets--> 这里开始进入uvc_camera库

(CameraDevice.ets/CameraManager.ets) --> CameraUtils.ets-->

-->CameraNativeMethods(index.d.ts文件，路径:

uvc_camera\src\main\cpp\types\libuvc_camera\index.d.ts)

-->camera_uvc.cpp-->(camera_factory_helper.h,camera->getUserStream())

其中camera->getUserStream()在ICameraDevice 中，是base类，有俩实现：

class CameraDeviceUsbImpl : public ICameraDevice

在camera_device_usb.h中，路径camera/usb，实现camera_device_usb.cpp

class CameraDeviceV4L2Impl : public ICameraDevice

在camera_device_v4l2.h中，路径camera/v4l2

这里分析camera_device_usb.cpp

-->CameraStreamUsbImpl(camera_stream_usb.cpp)-->(prepare_preview,do_preview):

prepare_preview-->(uvc_get_stream,uvc_get_frame_desc，这俩方法都指向stream.c，路径:

uvc_camera\src\main\cpp\libuvc\src\stream.c)

do_preview-->uvc_start_streaming-->stream.c-->uvc_start_streaming-->

(uvc_stream_open_ctrl,uvc_stream_start):

uvc_stream_open_ctrl-->(_uvc_get_stream_if,uvc_claim_if,uvc_stream_ctrl)

uvc_stream_start-->(uvc_find_frame_desc_stream,

libusb_fill_iso_transfer/libusb_fill_bulk_transfer,

pthread_create(&strmh->cb_thread, NULL, _uvc_user_caller, (void *)strmh);

libusb_submit_transfer)

-------------------------------------------------------------------------------------------------------------

这里根据红绿蓝三颜色分别分析：

一：

libusb_fill_iso_transfer-->_uvc_stream_callback-->(

_uvc_process_payload 或者

(pthread_cond_broadcast(&strmh->cb_cond);

pthread_mutex_unlock(&strmh->cb_mutex);))

这里根据LIBUSB_TRANSFER_XXX状态不同会走不同的路径，而libusb_fill_bulk_transfer和libusb_fill_iso_transfer一样都会走_uvc_stream_callback，路径一致

二:

pthread_create(&strmh->cb_thread, NULL, _uvc_user_caller, (void*)strmh

-->_uvc_user_caller--->(_uvc_populate_frame,

pthread_mutex_unlock(&strmh->cb_mutex);
strmh->user_cb(&strmh->frame, strmh->user_ptr);

)。

三：libusb_submit_transfer-->io.c-->libusb_submit_transfer

其中:_uvc_process_payload-->_uvc_swap_buffers

-->(pthread_cond_broadcast(&strmh->cb_cond);
pthread_mutex_unlock(&strmh->cb_mutex);)

数据是从linux_usbfs.c 中来的，从打开流到关闭流的整个过程，这里都会不停地打印：

op_submit_transfer:2

submit_bulk_transfer

handle_bulk_completion

op_submit_transfer:2

submit_bulk_transfer

_uvc_user_caller

而在获取参数的过程中：

就会开始不停地打印：

op_submit_transfer:0

submit_control_transfer

handle_control_completion

直到打开后突然就变成：

op_submit_transfer:2

submit_bulk_transfer

然后: _uvc_user_caller

而_uvc_user_caller方法见下：

do {
    LOG_D("_uvc_user_caller");
    pthread_mutex_lock(&strmh->cb_mutex);
    while (strmh->running && last_seq == strmh->hold_seq) {
        pthread_cond_wait(&strmh->cb_cond, &strmh->cb_mutex);
    }
    if (!strmh->running) {
        pthread_mutex_unlock(&strmh->cb_mutex);
        break;
    }
    last_seq = strmh->hold_seq;
    _uvc_populate_frame(strmh);
    pthread_mutex_unlock(&strmh->cb_mutex);
    strmh->user_cb(&strmh->frame, strmh->user_ptr);
} while (1);

这里能否继续执行取决于&strmh->cb_cond，搜索&strmh->cb_cond发现多出调用了：

pthread_cond_broadcast(&strmh->cb_cond);
pthread_mutex_unlock(&strmh->cb_mutex);

如：_uvc_swap_buffers

_uvc_stream_callback

uvc_stream_stop

而在linux_usbfs.c中的执行是：

op_handle_events-->reap_for_handle-->r = ioctl(hpriv->fd, IOCTL_USBFS_REAPURBNDELAY, &urb);

-->handle_bulk_completion(itransfer, urb);-->usbi_mutex_unlock(&itransfer->lock);

或者是

op_submit_transfer-->submit_bulk_transfer-->ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urb);

然后通过itransfer的数据和状态变化，或者唤醒？调用_uvc_stream_callback ?? 这样就会和下面这段连接起来

而在stream.c中一般是通过：uvc_stream_start(开始执行一次)-->

_uvc_stream_callback

-->_uvc_process_payload

(_uvc_process_payload(strmh, transfer->buffer, transfer->actual_length);)-->

(

        if (header_info & UVC_STREAM_EOF || strmh->got_bytes == strmh->cur_ctrl.dwMaxVideoFrameSize) {
            //来交换缓冲区，表示已接收完整帧
            _uvc_swap_buffers(strmh);
        }