Right now this is still hacky. I had to fix many aspects of Marcel's CardBoot program, and because I am out of AT27C1024 write-once ROMs, I am using a SD card that is bizarrely formatted to work around the limitations of the CardBoot burnt in my last ROM. Also CardBoot is very slow (it takes about 20 seconds. I cut the video). But this is on a good track. The browser code (https://github.com/lb3361/gigatron-os/tree/master/sys1, to be documented) needs to be computed with the very last version of GLCC (to be documented as well) and you need the latest v5a DEVROM to have the proper SYS_CopyMemoryExt and CardBoot.gt1.
The reason for my early post is in fact a hardware mystery. See how my VGA screen flickers and woobles around 0:30 when I am loading at67's Boing demo. This happens whenever I am quickly switching banks or maybe merely accessing different banks in quick succession. It is worse when accessing the SD, but also happens to a lesser extent when copying things across banks. Yet everything seems to work fine. I would be grateful if people more experienced in hardware could help me prune the list of possible culprits. These are much harder to debug than software (for me at least.)
- Timing error in SYS_CopyMemoryExt. Running them in at67's emulator doesnt show timing issues.
- Power issues. I tried a stronger power supply to no effect.
- Decoupling issues. My expansion card has 33nF capacitors near each chip. I noticed Hans61's card has 100nf capacitors. Could that be the problem?
- GAL glitches or excessive power requirements?
- Interferences with the VGA cable. The Gigatron is not exactly RF friendly ?
- Something else?