Mord's Blog - Maria/Sally split rom?

RSS Bot · November 18, 2006

Just a random thought I had while procrastinating on the display half-asleep. (I will work on the kernel again this weekend darnit!!)

The halt line controlled by Maria on the 7800 extends out to the cartridge. So what if that line was tied to the highest address line on a 17-address-line rom? Since the HALT line effectively identifies which CPU is in control, it would automate the task of changing between a rom that Sally saw (filled with data tables, sound info, and algorithms/routines) and a rom that Maria saw that was filled completely with graphics data.

It would potentially be a headache to organize pointers to the graphics data, but I'm sure it'd be doable.

With my limited skillz at hardware, that should work just fine... although it would become a lot trickier if you tried to bankswitch the split roms as well. Bankswitching itself could be easily done, but Maria and Sally would always change their banks to look at the same thing. (Well, more accurately, when Sally changes her bank, Maria's will be changed as well.) This could be a Bad Thing if Sally needed to change banks often for some reason (Maria could be trying to display the screen on different scanlines and be looking at different banks on different lines!) so ideally Sally's active bank should be independantly selectable from Maria's active bank, unless bankswitching is kept to a minimum (to limit excessive data/graphics duplication) or used intelligently. At which point having them tied would be fine.

Ok time to sleep. I'll work on the display when I wake up. I've been reading over skipdraw and vdel for the last couple of days and I think I know how I can use them properly. Now it's just matter of trying to write it up, then spend a week debugging the monstrosity I'll end up with.

http://www.atariage.com/forums/index.php?a...;showentry=2368