Search found 10 matches

by wbrian
Mon Jan 21, 2019 8:34 pm
Forum: NESemdev
Topic: Looking for clarification on bg shifts and output pixels
Replies: 0
Views: 9547

Looking for clarification on bg shifts and output pixels

I'm looking at the PPU rendering docs and am looking for some clarification. The first point of clarification is during which cycles the background shift registers shift: Every cycle, a bit is fetched from the 4 background shift registers in order to create a pixel on screen. https://wiki.nesdev.com...
by wbrian
Sat Jun 16, 2018 9:54 pm
Forum: NESemdev
Topic: Question about emulating UxROM mapper (mapper 002)
Replies: 3
Views: 3518

Question about emulating UxROM mapper (mapper 002)

I have a few questions about emulating mapper 002. I've been looking at https://wiki.nesdev.com/w/index.php/UxROM as a reference. - The documentation lists the address for the bank select register as "($8000-$FFFF)". This is confusing because it lists an address range. How should this be interpreted...
by wbrian
Sat Apr 22, 2017 11:34 am
Forum: NESemdev
Topic: Confusing byte format in APU docs
Replies: 3
Views: 2208

Confusing byte format in APU docs

I'm reading through the triangle generator docs here and I had a question about the following snippet: DPCM samples must begin in the memory range $C000-FFFF at an address set by register $4012 (address = %11AAAAAA.AA000000). The length of the sample in bytes is set by register $4013 (length = %LLLL...
by wbrian
Sun Apr 09, 2017 10:05 am
Forum: NESemdev
Topic: Sprite evaluation timing clarification
Replies: 2
Views: 2918

Re: Sprite evaluation timing clarification

Much appreciated! One more thing I could use clarification on: if eight in-range sprites have been found so far, the sprite evaluation logic continues to scan the primary OAM looking for one more in-range sprite to determine whether to set the sprite overflow flag. Does this imply that once sprite o...
by wbrian
Thu Apr 06, 2017 10:17 pm
Forum: NESemdev
Topic: Sprite evaluation timing clarification
Replies: 2
Views: 2918

Sprite evaluation timing clarification

I'm reading the wiki page on sprite timing here , and just wanted to clarify something quickly. Cycles 65-256: Sprite evaluation On odd cycles, data is read from (primary) OAM On even cycles, data is written to secondary OAM (unless secondary OAM is full, in which case it will read the value in seco...
by wbrian
Sun Mar 26, 2017 3:59 pm
Forum: NESemdev
Topic: "If rendering is enabled..." clarification
Replies: 5
Views: 2405

Re: "If rendering is enabled..." clarification

Much appreciated! Thanks for the quick responses.
by wbrian
Sun Mar 26, 2017 2:53 pm
Forum: NESemdev
Topic: "If rendering is enabled..." clarification
Replies: 5
Views: 2405

Re: "If rendering is enabled..." clarification

Per https://wiki.nesdev.com/w/index.php/Glossary Forced blanking Turning off the rendering circuitry by writing zero to $2001, giving the CPU the same access to VRAM through the PPU ports that the CPU normally has during vertical blanking. I guess this is where I'm getting confused since it implies ...
by wbrian
Sun Mar 26, 2017 1:49 pm
Forum: NESemdev
Topic: "If rendering is enabled..." clarification
Replies: 5
Views: 2405

"If rendering is enabled..." clarification

I've been reading the scrolling docs on the wiki and the phrase "If rendering is enabled..." is encountered a lot. I'm just trying to clarify what it means for rendering to be considered "enabled." I'm interpreting it as: - Either bit 3 or 4 is set on PPUMASK - Not in Vlank or Forced blank Am I corr...
by wbrian
Thu Feb 16, 2017 9:32 am
Forum: NESemdev
Topic: Undefined opcodes in PRG rom
Replies: 9
Views: 4780

Re: Undefined opcodes in PRG rom

Thanks for the replies everyone, I have to digest some of this but it's mostly making sense. One thing I'm clearly doing wrong in my emulator is starting execution with PC = 0x8000, where instead it should start at 0xC000. Am in incorrect in believing that this should be mostly equivalent, though? F...
by wbrian
Wed Feb 15, 2017 6:55 pm
Forum: NESemdev
Topic: Undefined opcodes in PRG rom
Replies: 9
Views: 4780

Undefined opcodes in PRG rom

I'm writing a NES emulator and the CPU is fully implemented, and I'm currently implementing memory mapping to all the other components (PPU, APU, etc), initially only mapping with NROM in mind. I'm not at the point where I'm actually drawing pixels, but I'm able to load and execute NES roms, and it'...