Search found 159 matches

by gravelstudios
Mon Mar 20, 2023 6:24 am
Forum: SNESdev
Topic: SNES PPU Warmup Period?
Replies: 7
Views: 995

SNES PPU Warmup Period?

Does the SNES have a PPU warmup period like the NES, or is it ready to go as soon as the console is powered up?
by gravelstudios
Sun Mar 12, 2023 12:26 pm
Forum: NESdev
Topic: DPCM + $2007 reads
Replies: 22
Views: 1796

Re: DPCM + $2007 reads

DPCM glitches cause byte deletions, not incorrect bytes, so it's not going to be a matter of going back and fixing the single errors - it's going to be a matter of restarting where you detected the error. Ah, I see. thanks for the clarification. Other than being a lot slower, would there be an issu...
by gravelstudios
Sun Mar 12, 2023 10:16 am
Forum: NESdev
Topic: DPCM + $2007 reads
Replies: 22
Views: 1796

Re: DPCM + $2007 reads

Would it be unacceptable to just disable the DMC channel for the time it takes to copy the data? That seems like the simplest solution to me. If you really don't want to disable the DMC channel, then what I'd do is read all the data through $2007 that you want to preserve, then read it a second time...
by gravelstudios
Fri Mar 03, 2023 9:29 am
Forum: Other Retro Dev
Topic: Interesting Video about 6502 "broken" ROR
Replies: 4
Views: 1534

Interesting Video about 6502 "broken" ROR

An interesting YouTube video in which the narrator claims the ROR instruction on the first version of the 6502 was not broken as has long been assumed, but was left intentionally unimplemented as a design choice:

https://www.youtube.com/watch?v=Uk_QC1eU0Fg
by gravelstudios
Fri Mar 03, 2023 4:44 am
Forum: Newbie Help Center
Topic: 6502 Division Routine
Replies: 5
Views: 993

Re: 6502 Division Routine

Gilbert wrote: Thu Mar 02, 2023 10:29 pm There is a division routine in the Wiki:
https://www.nesdev.org/wiki/8-bit_Divide
This is the one I was referring to in my original post.
by gravelstudios
Thu Mar 02, 2023 1:52 pm
Forum: Newbie Help Center
Topic: 6502 Division Routine
Replies: 5
Views: 993

6502 Division Routine

I'm hoping other people may find this helpful. Performing division with arbitrary values is something I think a lot of beginner 6502 programmers struggle with (I know I did). There is code on the wiki for how to do it, but I had a hard time understanding what exactly that code was doing. I recently ...
by gravelstudios
Sun Feb 19, 2023 6:34 am
Forum: NESdev
Topic: Best way to detect NTSC or PAL
Replies: 59
Views: 14101

Re: Best way to detect NTSC or PAL

Thank you all for your feedback. I think now I'm leaning more strongly in the direction of making it a setting the player toggles. That seems like the easiest solution to me.
by gravelstudios
Fri Feb 17, 2023 9:37 am
Forum: NESdev
Topic: Best way to detect NTSC or PAL
Replies: 59
Views: 14101

Re: Best way to detect NTSC or PAL

Not a specific value, no. I'm incrementing X as a low byte, and then Y as a high byte on iterations where X=0. Then I only check the value of Y. So it gives a range but there's plenty of wiggle room: LDX #0 LDY #0 PPUWait2: INX BNE .NoYInc INY .NoYInc: BIT $2002 BPL PPUWait2 I did my math based on t...
by gravelstudios
Fri Feb 17, 2023 7:46 am
Forum: NESdev
Topic: Best way to detect NTSC or PAL
Replies: 59
Views: 14101

Re: Best way to detect NTSC or PAL

To detect the region, in my init code, I do the first poll on $2002, then clear memory as usual, and then measure the remainder of that frame with a $2002 poll. Because $2002 polling may miss a frame, I compare the resulting number against 5 thresholds to figure out which of the 6 possible ranges i...
by gravelstudios
Fri Feb 17, 2023 4:36 am
Forum: NESdev
Topic: Best way to detect NTSC or PAL
Replies: 59
Views: 14101

Re: Best way to detect NTSC or PAL

Thank you all for the advice. The only thing I want to do is run my music engine twice on every 5th frame on PAL machines to compensate for the slower framerate. So if the region doesn't get set properly, it's not the end of the world. I'm using the method of counting cycles between v-blanks during ...
by gravelstudios
Thu Feb 16, 2023 3:20 pm
Forum: NESdev
Topic: Best way to detect NTSC or PAL
Replies: 59
Views: 14101

Re: Best way to detect NTSC or PAL

Apologies for bumping this ancient thread, but I'm curious about this topic. I'm on the fence about whether I want to automatically detect the system a game is running on, or let the player toggle it for themselves. On one hand, I like the idea of it being handled automatically without the player ha...
by gravelstudios
Sun Feb 12, 2023 8:37 am
Forum: NESdev
Topic: Garbage Pail Kids Mapper?
Replies: 8
Views: 1258

Re: Garbage Pail Kids Mapper?

Thanks for the information!

I think what I would ideally like is something like UNROM with flashable memory (so the cart wouldn't need a battery), but also with some sort of IRQ capability for timing screen splits. Does that exist?
by gravelstudios
Sat Feb 11, 2023 1:22 pm
Forum: NESdev
Topic: Garbage Pail Kids Mapper?
Replies: 8
Views: 1258

Re: Garbage Pail Kids Mapper?

It's normal TKROM, and it has the usual scrolling glitches at the top and bottom of the screen, probably masked off by OP's TV or default emulator settings. You're right, the youtube video I was watching of it had the top and bottom 8 pixels masked off, and I didn't notice. I don't know what mapper...
by gravelstudios
Sat Feb 11, 2023 6:07 am
Forum: NESdev
Topic: Garbage Pail Kids Mapper?
Replies: 8
Views: 1258

Garbage Pail Kids Mapper?

Does anybody know what mapper Garbage Pail Kids uses? It seems to handle 4-way scrolling with no glitches, so I assume it has on-cart VRAM for all 4 nametables, but the game also contains multiple screen-splits for parallax scrolling, so it must also have IRQs. I'd love to use a mapper like that for...