Did it! – Mostly – But now I MUST do some family stuff :-).
Major stepping stones. –
Build environment – I run a debian Linux in a VM and do everything there, but this makes shuffling stuff to USB devices not any easier…
– Mode switch of GPIO done to soon after booting seems to HALT the Pi permanently – didn’t find any documentation on this.But just wait enough and it works for me.
– Slow as hell -> I had to activate the MMU unit and caching and jump prediction – MAJOR speedup (times 20-30)
Difficulties:- no debugging whatsoever, I did not have a mini UARTcable or anything else.- all I had was the green LED. I think I learned Morse code, the last hours!
TODO:- the version is again about 1/3 of the speed of the non bare metal, this mainly is due to compiler settings. For whatever reasons -O3 produces bad output, I suspect the „other” bcm library implementation – but I just tried once, just have to find the time…
– I still use „busy” waits, I might now try timers…- Further bettering of the output to Vectrex, now „undisturbed”