Today was a crazy day, and I really did not have time to work on this... But I still took an hour...

My analysis from yesterday is flawed - TI ROMs do not write to ROM area, instead something else must be wrong, and that could be very many things. Whatever it is, it causes the system go berserk and corrupt memory.

So the pepino FPGA board I'm using has one tactile switch. I made it behave as TI keyboard button "1" and expanded my test ROM app to show that indeed again here behaviour matches the classic99 emulator: when the button is pressed the CRU I/O space keyboard selection works properly, the appropriate bit follows my button. So I push the button with Basic ROMs and GROMs loaded - and no go. Screen becomes blank after the initial welcome screen. Okay, this could be a million things still. For example I don't have proper interrupts yet. Working backwards on what has been the least tested area of my FPGA functionality - the GROMs. And VDP reading. If one of them fails ever so slightly, especially GROM handling, the GPL interpreter is going to get very confused and may write all over the place, including the ROM. So I need to write a test app to really test GROM access, more that a few bytes, it needs to process and test through them a million times. VDP reading I have tested a bit more, so that might work.