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JSIGA.1
JSIGA.1
Associate II
December 15, 2021
Question

Interprocess communication buffer swapping

  • December 15, 2021
  • 4 replies
  • 1829 views

Hello,

I am working on IPC between M4 and A7 and it works properly using the "logic analyzer" example. I changed it according to my needs but not the buffers.

1 . I could read the data from 3 buffers, but often buffers are swapping. I would like to what causes this problem and how to solve it?

2. When I start IPC, one of the CPU processes goes into 100%. Is it normal for the IPC? and is there anything that I could change to reduce the CPU processes?

Thank you in advance

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4 replies

Olivier GALLIEN
Olivier GALLIEN
ST Technical Moderator
December 16, 2021

Hi @JSIGA.1​ ,

Can you please provide some more context ?

Which OpenSTLinux version ?

Custom or ST board ?

I understand that default logic analyze was working properly and reported issues comes only with your 'changed it according to my needs' right ?

Could you share details of those changes ?

Thx

Olivier

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JSIGA.1
JSIGA.1Author
Associate II
December 17, 2021

Hello Olivier,

I have a custom board which is based on stm32mp157A.

I am using openSTLinux Dunfell but i don't know which version exactly.

I am trying to send around 50kilobytes of data with frame numbers for every buffer from M4 to A7 in every 100ms. I have not touched the Sending part in logic analyze code of M4.

In A7, I haven't touched the reading part . When the buffer filled event occurred, I read the data and process those. (processing time of the 50kb data is 8 milliseconds in A7)

I am successfully reading the data without any frame loss or frame swapping from A7 for around 15 minutes. after that, the buffer swapping problem arises for a couple of buffers and disappeared, again in the next 2 or 3 mins, it appears again and disappeared.

Regarding my second question, I found a small bug in my code, which consumes a lot of CPU resources. after changing that the CPU usage has been reduced. but still, I have a buffer swapping problem.

JS

Olivier GALLIEN
Olivier GALLIEN
ST Technical Moderator
December 20, 2021

Hi @JSIGA.1​ ,

No evidence here.

I guess it deserve a careful system debug to try to catch the root cause.

Anyway, maybe one clue to evacuate would be a potential cache coherency issue as per already faced in this post :

https://community.st.com/s/question/0D53W00000uXp2hSAC/rpmsg-sdb-cached-buffer

I attached the recommended patch to apply in rpmsg_sdb driver.

Let us know.

Thx

Olivier

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JSIGA.1
JSIGA.1Author
Associate II
December 21, 2021

Hai,

I have tried changing to DMA coherent, but it didn't help me in my case. Still, the problem persists.

JS

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