Realsense: Handling USB Connection Errors and Ensuring Program Stability

[wataru-okumura]

I have always used realsense. Thanks for the daily updates.
I would like to discuss one point.

When using librealsense, you may keep getting the following error. It is probably caused by a bad USB connection.

[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135208000456256] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 69 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135208000456256] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 69 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135208000456256] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 69 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device
[realsense2_camera_node-1]  20/06 06:22:51,398 ERROR [135207783220800] (backend-v4l2.cpp:2970) xioctl(VIDIOC_QBUF) failed when requesting new frame! fd: 75 error: No such device

In this case, command operations on the console will be disabled and recovery will take time.
So, when such an error occurs (or continues to occur for a certain period of time), is it possible to change the code so that it throws an exception or otherwise terminates abnormally and appropriately without running out of control?

[MartyG-RealSense]

Hi @wataru-okumura xioctl errors are typically related to a conflict between the librealsense SDK and the Linux kernel.

I have seen an example of C++ code that tries to catch this error and handle it.

if (-1 == Xioctl(VIDIOC_QBUF, &mCurBuf))
ErrnoExit("VIDIOC_QBUF during mainloop");

https://stackoverflow.com/questions/29704406/is-it-possible-to-get-good-fps-using-raspberry-pi-camera-v4l2-in-c

An alternative to using a catch would be to build librealsense from source code with CMake with the flag -DFORCE_RSUSB_BACKEND=TRUE included in the CMake build instruction. An RSUSB build of the SDK bypasses the kernel.
Instructions for an RSUSB build can be found at #9931 (comment)

[wataru-okumura]

Sorry for the late reply.
I am currently using the camera via your realsense-ros package.
Do you have any plans to implement code that would allow the realsense-ros package to detect xioctl errors emitted by the librealsense SDK?

[MartyG-RealSense]

It's no problem at all.

xioctl errors are kernel messages, so if you need to check if they have occurred then you could examine the kernel log using the information at the RealSense troubeshooting documentation link below.

https://dev.intelrealsense.com/docs/troubleshooting#general-linux-kernel-log