GXL

[dsx724]

1. Lock CPU Frequency sudo cpufreq-set -f 1GHz
2. Isolate CPUs 1, 2, and 3 and Assign Task via taskset -c
3. Disable nohz via cmdline by adding nohz=off to /etc/default/grub
4. Use a Schmitt-Trigger Inverter to handle level shifting, signal conditioning, and inversion for UART.

[guysoft]

What is this list?

[dsx724]

@guysoft This is the setup requirements for GXL based platforms including S805X, S905X, S905D. As Linux is not an RTOS, scheduling and context switching can result in UART buffer underrun which would cause glitching of the LEDs. The instructions here are requirements for glitch-free operation of the LEDs. The last one is an external hardware requirement for cleaning up the waveforms since LED signal has non-trivial capacitance.

[guysoft]

Ok, so for taskset -c you need to provide the command?
So something like this?:

taskset -c 1 bash -x ./run.sh ./config/ws2812-uart-gxl-aml6.ini

What do you mean by Isolate CPUs 1, 2, and 3?

[dsx724]

@guysoft In order for the signal to the LEDs to not glitch, you need to make sure the UART buffer never underrun. The buffers on GXL are either 64B or 128B. Context switches and other factors can affect the component step completion time. It's best to disable 2 or 3 CPUs from the kernel scheduler, making them completely idle, and manually assigning processes to run on those CPUs only. CPU DVFS also affects completion time.

[guysoft]

OK it works for me, it just load really really fast so I had to slow down the for loop. I think now rewriting rgb-bg-step in python and then it would be easier for friend who write in that to get more complex led patterns going

[dsx724]

Be aware that python is a much slower language than PHP.

[guysoft]

Well aware :)
For now I translated only rgb-bg-step. I could use some C++ bindigs to speed it up, but not sure python or PHP would be the best thing to write drivers in.

I think it might make sense to translate ws2812-uart and run.sh to something other than PHP to reduce dependencies. Something like C++ or go. But for now it works, and I can pass the python script. I am working on making a small Le Potato distribution that boots and lets you drive LEDs.