Linux: AM335x USB issue with DVFS

Ravikiran HV

Tool/software: Linux

Hello experts,

We are using AM335x with latest 4.9.x linux kernel release from TI.
We enabled "ONDEMAND" frequency governor to scale the frequency between 300MHZ-800MHz. Entire system works well with this configuration except USB.

We have a USB camera connected to AM335x to capture video using V4L2 application. @300MHz,@600MHz,@720MHz & @800MHz we are able to capture and playback the recorded video (Video @VGA resolution).
However, when frequency scaling enabled "ONDEMAND", frequency dynamically changes b/w 300MHz to 800MHz and randomly some video frames are lost in the middle. This leads to some "break" in the video.

On inspecting ADPLLLJ & ADPLLS, USB phy clock and OCP clocks have no bypass clock. So, during frequency change, we can't force USB to bypass mode. Please can you suggest a better alternate here?

Thanks

over 7 years ago

0 Bin Liu over 7 years ago

TI__Guru**** 177101 points

Ravikiran,

Can you please elaborate the "break" in the video? Is this any full video frame drop which causes the non-smooth video streaming or corrupted video frames for example video tearing?

I doubt it is the clock rate transitioning which directly causes the issue, you would have to debug the usb driver stack to understand the abnormal usb transfers.

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

Hi Bin,

This is the video tearing. Couple of frames are corrupted partially in the middle of the frame.

I suspected USB clocking during transition with governor because, we never saw this problem when "ondemand" governor is Disabled !
Video is perfectly fine in All DDR/ARM clocks. However, on the go "on-demand" governor causes this problem.

Thanks

0 Bin Liu over 7 years ago in reply to Ravikiran HV

TI__Guru**** 177101 points

Ravikiran,

What application do you use to stream the video from the usb webcam? If it is gstreamer, what is the gst pipeline?

Do you directly stream the video on LCD or external display? or save the video to a file and review it offline? If former, can you please try to save the video to a file and play it back on PC to see if the tearing still happens? I am trying to see if we can isolate the issue is in v4l2 or usb layer.

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

I am using this application.
github.com/.../capture-example.c

0 Bin Liu over 7 years ago in reply to Ravikiran HV

TI__Guru**** 177101 points

I am not familiar with this capture application. How do you use it to review the webcam video stream? I asked you more questions in my previous post, but you only answered one...

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

HI Bin,

This is a V4L2 based application.
We store the video data to DDR (queue) first and then write it to file.

For inspection, we transferred theses videos to PC and played in VLC. VLC playback shows video tear down issue

Thanks

0 Bin Liu over 7 years ago in reply to Ravikiran HV

TI__Guru**** 177101 points

Ravikiran,

What camera do you use, such as model number and VID/PID?
I will be out of office for two week. I will try to reproduce it once I am back.

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

BIN,

We used different variants of USB camera's such as logitech C130/C170 and observed similar behaviour.

Thanks

0 Bin Liu over 7 years ago in reply to Ravikiran HV

TI__Guru**** 177101 points

Ravikiran,

Sorry for my late response. I am unable to replicate the tearing issue. Can you not use the on-demand scaling to avoid this issue?

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

Hi Bin,

For now, we have disabled on demand. But, it will be great if you can help us to enable this feature.

Thanks

0 Bin Liu over 7 years ago in reply to Ravikiran HV

TI__Guru**** 177101 points

Ravikiran,

There is nothing much I can do at this moment as I am unable to replicate the issue.

Can you please test the community newer kernel for example v4.14 or v4.17? You can download it from kernel.org, and build with omap2plus_defconfig, it will boot on am335x board.

0 Bin Liu over 7 years ago in reply to Bin Liu

TI__Guru**** 177101 points

Hi, I haven’t heard back from you, I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out). thanks.

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

Hi Bin,

Thanks for the followup.

I haven't tested with new kernels as it is not TI official release, which may end up in new set of unknown issues.
However, I can confirm that the issue exists on 4.9.x kernel still (TI official release).

As indicated in last email, we are using fixed freq to get rid of the problem for now. But that is not the solution we are looking for :)

0 Ravikiran HV over 7 years ago in reply to Bin Liu

Mastermind 8715 points

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Linux: AM335x USB issue with DVFS