UVC摄像头USB批量传输BULK数据传输方式的打开与关闭StreamOn StreamOff

USB的批量传输和中断传输是一样的简单，但经常发现有人在问批量传输的UVC摄像头的打开与半闭问题的边界问题，特别是摄像头关闭的判断。

BULK摄像头的打开

我们通过BUSHOUND抓包的内容如下：

Device  Length    Phase  Data                                                                                                    Description   
------  --------  -----  ------------------------------------------------------------------------------------------------------  --------------
  42.0            CTL    a1 81 00 01  01 00 22 00                                                                                GET CUR       
  42.0        34  IN     01 00 01 01  15 16 05 00  00 00 00 00  00 00 00 00  00 00 00 a4  1f 00 0c 48  3f 00 00 00  00 00 03 01  ..............
  42.0            CTL    21 01 00 01  01 00 22 00                                                                                SET CUR       
  42.0        34  OUT    01 00 02 02  15 16 05 00  00 00 00 00  00 00 00 00  00 00 00 a4  1f 00 00 00  00 00 00 00  00 00 03 01  ..............
  42.0            CTL    a1 81 00 01  01 00 22 00                                                                                GET CUR       
  42.0        34  IN     01 00 02 02  15 16 05 00  00 00 00 00  00 00 00 00  00 00 00 90  7e 00 0c c8  00 00 00 00  00 00 03 01  ..............
  42.0            CTL    a1 83 00 01  01 00 22 00                                                                                GET MAX       
  42.0        34  IN     00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  ..............
  42.0            CTL    a1 82 00 01  01 00 22 00                                                                                GET MIN       
  42.0        34  IN     00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  00 00 00 00  ..............
  42.0            CTL    21 01 00 02  01 00 22 00                                                                                SET CUR       
  42.0        34  OUT    01 00 02 02  15 16 05 00  00 00 00 00  00 00 00 00  00 00 00 90  7e 00 0c c8  00 00 00 00  00 00 03 01  ..............
  42.0            CTL    01 0b 00 00  01 00 00 00                                                                                SET INTERFACE 
  42.1     51200  IN     0c 80 00 00  00 00 00 00  00 00 00 00  00 00 00 01  40 01 0c 01  ff ff 01 60  00 00 03 00  00 03 00 00  ..............

可以看到，通过复杂的UVC特定类请求GET_CUR,SET_CUR等，最终VS_PROBE_CONTROLL/VS_COMMIT_CONTROL之后，然后SET_INTERFACE之后，通过BULK端点0x81获取到了数据。
关于其具体的类似分析可参见：https://www.usbzh.com/article/detail-105.html

而通过南京沁恒的USB总线分析仪USB2.0 Monior抓到的数据类示：

BULK摄像头的关闭

通过BUSHOUND抓到的BULK数据传输的关闭摄像头的内容如下：

42.1     45388  IN     0c 83 00 00  00 00 00 00  00 00 00 00  00 00 00 01  02 01 d0 00  2d c4 0e e0  8b 42 8e f3  ef d8 f2 2f 
42.0            CTL    01 0b 00 00  01 00 00 00                                                                                SET INTERFACE

可以看到就是简单的SET_INTERFACE,但是通过USB总线分析仪就是再是这么简单了：

可以看到，这里的关键点其实是:

02 01 00 00 81 00 00 00

通过USB标准请求及描述符在线分析解析为：

0x02,        // bmRequestType: Dir: H2D, Type: Standard, Recipient: Endpoint
0x01,        // bRequest (Clear Feature)
0x00, 0x00,  // wValue Feature Selector: 0
0x81, 0x00,  // wIndex Endpoint: 0x81 (IN/D2H)
0x00, 0x00,  // wLength = 0

// 8 bytes

可以看到，其对应的是CLEAR_FEATURE,对比USB 清除特性请求ClearFeature https://www.usbzh.com/article/detail-89.html 一文可知:
这是对于端点的停止特性ENDPOINT_HALT.

所以这也证明了,BUSHOUND抓到的包并不一定是USB总线上的数据包，但大部分是。只是因为其所在的层次不同，故数据不同。