Thank you for your answer.
I already read this document, but I’m more interested in the detailed one, describing for example the addresses of DMA channels and other stuff closer to the hardware bypassing the OS. For example I’d like to adapt this library https://github.com/metachris/RPIO to the Radxa Zero.
MRAA is nice, but isn’t fitted to my use. Ultimately, I’d like to recycle a Raspberry Pi daugther board which drives a set of ws281x leds and some other stuff.
Benoît