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Castlevania bug(?)
Posted: Sun Oct 23, 2011 8:33 pm
by James
I spent a bunch of time over the weekend trying to fix what I thought was a bug with my emulator, but I'm pretty sure it's a bug in Castlevania.
Right before the last level starts, after Simon walks across the map screen, a bunch of garbage will briefly appear on the screen. I first noticed this after changing NMI timing to fix another game. I assumed I had a bigger problem since this glitch doesn't appear in Nestopia or Nintendulator.
It does, however, appear in a couple of youtube videos recorded off of real systems:
http://www.youtube.com/watch?v=5bzkUlwH ... re=related @ 0:08
http://www.youtube.com/watch?v=cezc5uq2 ... re=related @ 5:08
Posted: Sun Oct 23, 2011 8:34 pm
by Dwedit
There's two different revisions of Castlevania, do they both behave the same way?
Posted: Sun Oct 23, 2011 8:37 pm
by James
yes, tested both PRG0 and PRG1.
Posted: Sun Oct 23, 2011 8:54 pm
by MottZilla
I don't recall it happening on my NES. Could it be as timing critical as to be affected by cpu/ppu relative sync? Maybe there is a recording of real hardware that won't have the glitch because of some sort of critical timing chance.
Posted: Sun Oct 23, 2011 9:00 pm
by 6T4
Just wanted to point out that it could be something to do with NTSC vs. PAL, I believe they have different refresh rates.
Posted: Sun Oct 23, 2011 9:04 pm
by James
MottZilla wrote:I don't recall it happening on my NES. Could it be as timing critical as to be affected by cpu/ppu relative sync? Maybe there is a recording of real hardware that won't have the glitch because of some sort of critical timing chance.
Maybe. Just found another one though:
http://www.youtube.com/watch?v=ONntlxVJS5g @ 21:19
Posted: Mon Oct 24, 2011 9:59 am
by MottZilla
I'm gonna have to try this on my NES.
Posted: Mon Oct 24, 2011 1:03 pm
by Zepper
I can only speculate it. SMB1 has a similar thing, just pay attention. Well, looks like the screen rendering seems to stay enabled for a few moments. Probably a programmer's error.
Posted: Mon Oct 24, 2011 1:17 pm
by Dwedit
Castlevania is PRG only, it uses VRAM. No bankswitching, just CHR writes. Maybe they left the screen on for an extra frame before updating the nametables.
Posted: Mon Oct 24, 2011 3:45 pm
by Zepper
Dwedit wrote:Castlevania is PRG only, it uses VRAM. No bankswitching, just CHR writes. Maybe they left the screen on for an extra frame before updating the nametables.
Right, my mistake here, I was with Castlevania
3 in mind. Sorry.
Posted: Mon Oct 24, 2011 5:27 pm
by MottZilla
If it is an error, curious why it apparently only happens when that particular stage begins.