0RaymondJiang0

0RaymondJiang0

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0RaymondJiang0 issue comment hzeller/rpi-rgb-led-matrix

0RaymondJiang0
0RaymondJiang0

--led-slowdown-gpio=5 not enough on Pi 4 with long chain

Hi @hzeller, first off thank you for creating this excellent library. The documentation is fantastic and has been very useful to get started.

I'm having an issue running a long-ish chain of 32x64 P5 panels from a Pi 4 + active-3 hat where --led-slowdown-gpio=5 produces tearing in the final panels. Running a chain of 12 panels from a single output, I get ~500Hz refresh with the final 4 panels showing bad artifacts:

https://user-images.githubusercontent.com/6807187/143264894-b5440046-e7bf-44b3-8610-5f26286d9e60.mp4

If I modify led-matrix.cc line 621 to allow for gpio_slowdown > 6 and then run the demo with --led-slowdown-gpio=6 it resolves the tearing issues in all panels, however I'm then limited to ~60Hz:

https://user-images.githubusercontent.com/6807187/143265414-48ec6965-09c0-4f4d-bbc2-c57b96fc0bc0.mp4

Given that slowdown =5 runs fine for the first 8 panels at 500Hz I assume there's some middle ground to be found here? I haven't had a chance to dig into the library further to see how you're implementing gpio_slowdown in the runtime options struct, but is there something you recommend testing next? Limiting the refresh rate using --led-limit-refresh=x while running --led-slowdown-gpio=5 doesn't change anything, even if I drop it down to 60Hz.

Thanks!

0RaymondJiang0
0RaymondJiang0

@ntwallace Thank you very much! I meet the same problem, modify led-matrix.cc line 621 to allow for gpio_slowdown > 6. It works for me.

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