Troubleshooting artifacts after exhausting options for an 128x64 ABC panel

[taintedkernel]

Hello, I'm having difficulty getting an 128x64 ABC panel to function without artifacts/glitches. I've also been testing a chain of 4 64x32 displays and after identifying a number of issues I finally have these working without problems, but the native 128x64 panel still has problems.

I'm using an Adafruit RGB Matrix Bonnet on a new RPi 4 with the anti-flicker hardware mod. Recorded 2 videos, one of the artifacts on the native panel and one with the 4 panel combo working flawlessly - https://photos.app.goo.gl/5c3Et18sRQHtYzeq8

Things I've tried:

• Larger 5V PSU @ 10A
• Soldered low-ESR caps to the 5V power lines at the connector to PCB
• Tried older v4 kernels since I was aware of other issues with GPIO speed on newer kernels (https://github.com/raspberrypi/linux/issues/3381)
• Moved from Raspbian to DietPi (this helped a great deal)
• Tinkered with all available options in the software (led-pwm-lsb-nanoseconds=50 had the best results)
• Other tips also done (disabled sound, no GUI, isolcpus=3, etc)

The only other thing that stuck out to me was the mention of a low logic level voltage, but the Adafruit adapter says it has level shifters onboard. The HUB75 data cable is only about 5" long.

As mentioned, the hardware works flawlessly (now) with a set of 4 displays giving me a combined 128x64, so I think the problem is with the larger panel or limitations with the ABC addressing.

Thanks for this project and your time! Appreciate any suggestions :smile: