Question on Golden Axe II
Posted: Fri Apr 02, 2021 8:04 pm
I notice my emulator is getting a garbled "Sega" logo screen, and partially garbled intro screen immediately after it.
Looking at the trace, it loads d0 with #$ffffffe3, and then shortly after just starts spamming loop: move.l (a0)+,($c00000); dbf loop; instructions for big ~64K loops from ROM to VRAM, filling it with pure junk basically.
I confirmed via Mednafen that it really does do this. Source+target address is correct, it really does spam hundreds of thousands of writes to the data port to send to VRAM. The VRAM address it's writing to loops around back to the beginning a few times even, so it's clearly nonsensical. I thought at first it'd be VDP FIFO limiting how much data it could get across, but Mednafen doesn't seem to emulate the FIFO. If I try to simulate 16-18 transfers per active display line, 85-105 transfers per blanking line, it just slows down how long before the garbled "Sega" screen appears, and doesn't really affect the result much.
I must be missing something here. Anyone here wrestle with this game before by chance? ^-^;
Looking at the trace, it loads d0 with #$ffffffe3, and then shortly after just starts spamming loop: move.l (a0)+,($c00000); dbf loop; instructions for big ~64K loops from ROM to VRAM, filling it with pure junk basically.
I confirmed via Mednafen that it really does do this. Source+target address is correct, it really does spam hundreds of thousands of writes to the data port to send to VRAM. The VRAM address it's writing to loops around back to the beginning a few times even, so it's clearly nonsensical. I thought at first it'd be VDP FIFO limiting how much data it could get across, but Mednafen doesn't seem to emulate the FIFO. If I try to simulate 16-18 transfers per active display line, 85-105 transfers per blanking line, it just slows down how long before the garbled "Sega" screen appears, and doesn't really affect the result much.
I must be missing something here. Anyone here wrestle with this game before by chance? ^-^;