Search found 4453 matches

by Dwedit
Sat Jun 19, 2021 12:06 pm
Forum: NESdev
Topic: MMC3 on FPGA?
Replies: 3
Views: 692

Re: MMC3 on FPGA?

Try looking at an FPGA NES project, it would have an implementation of the MMC3 as part of supporting mappers. Also make sure the author is okay with you using their Verilog code, check the software license, etc...
by Dwedit
Sat Jun 19, 2021 11:58 am
Forum: NESemdev
Topic: Sprite 0 hit test corrupts my PPU
Replies: 1
Views: 65

Re: Sprite 0 hit test corrupts my PPU

I haven't written such a PPU yet, but my design would be to only perform rendering at times when the CPU and PPU need to be synchronized. Examples of times when the CPU and PPU need synchronization: CPU affects what PPU draws: * Scrolling * CHR Bankswitching * PPU control bit changes * PPU mask bit ...
by Dwedit
Thu Jun 10, 2021 11:11 am
Forum: NESemdev
Topic: Mesen - NES Emulator
Replies: 963
Views: 577148

Re: Mesen - NES Emulator

It is notably hard to find mkwong98's repository using the Network feature on Github. If you start at the SourMesen repository, and look at "Network", it picks the name of the most recent person who imported changes from that repository. mesen-active-github2.png When I looked a couple days ago, it l...
by Dwedit
Wed Jun 09, 2021 7:42 pm
Forum: NESdev
Topic: Problem with palette discoloration when PPU is turned off during rendering.
Replies: 15
Views: 1962

Re: Problem with palette discoloration when PPU is turned off during rendering.

Maybe multiple bootups to get the right PPU/CPU sync?
by Dwedit
Wed Jun 09, 2021 9:57 am
Forum: NESemdev
Topic: Handling Illegal Opcodes
Replies: 10
Views: 1199

Re: Handling Illegal Opcodes

You should not be encountering illegal opcodes. Real games uses these very rarely (but a few do). If you encounter illegal instructions, it usually means you are doing something wrong. First thing to confirm is that you are starting the program at where the Reset Vector says to begin, and not the fi...
by Dwedit
Tue Jun 08, 2021 6:24 pm
Forum: NESemdev
Topic: Mesen revival (attempt)
Replies: 2
Views: 784

Re: Mesen revival (attempt)

There's already a thread for Mesen on this forum here. I know that monstrously big threads are hard to read. But people are mainly looking at the new posts there. https://forums.nesdev.com/viewtopic.php?f=3&t=13844 Github's "Network" view is not doing a good job of pointing to the active forks which...
by Dwedit
Thu Jun 03, 2021 3:53 pm
Forum: NESdev
Topic: Scanlines to CPU cycles
Replies: 4
Views: 816

Re: Scanlines to CPU cycles

341 PPU dots per scanline, or about 113 CPU cycles.
Is the approximation (128 * X) - (16 * X) for 114 CPU cycles per scanline fast and simple enough?
Or (128 * X) - (16 * X) - X for 113 cycles per scanline.
by Dwedit
Wed Jun 02, 2021 10:18 am
Forum: NESdev
Topic: NES trainers
Replies: 9
Views: 1020

Re: NES trainers

It's just like any other NES rom hacking.
Find some empty space in the ROM, write your code, and find some existing code to modify to call or jump to your new code.
The debugger feature of emulators can help here.
by Dwedit
Tue Jun 01, 2021 7:28 pm
Forum: NESdev
Topic: NES dev on retro pc
Replies: 20
Views: 2209

Re: NES dev on retro pc

A two-pass assembler doesn't need to keep everything in RAM.
It can stream the input source files and output binary file.
Symbol Table could either be in RAM, or if RAM is really tight, even be on the disk.
by Dwedit
Tue Jun 01, 2021 4:39 pm
Forum: NESemdev
Topic: FCEUX palette origins?
Replies: 4
Views: 769

Re: FCEUX palette origins?

Where do NES colors come from? They come from a 12-step square wave that alternates between two voltages, and being interpreted in the YIQ color space. I would say that the Nintendulator palette is pretty much the perfect NES palette. It looks nice and colorful, and it's based on the actual math a T...
by Dwedit
Mon May 31, 2021 9:59 am
Forum: NESdev
Topic: What are ROM Nametables useful for?
Replies: 15
Views: 5446

Re: What are ROM Nametables useful for?

For ROM Nametables to be useful, you need to have a static screen that will never change, and a need to switch between multiple static screens quickly. Thus, they were used for Flight-Sim type games like After Burner, or Racing games. I think one of the Street Fighter bootlegs also uses ROM Nametabl...
by Dwedit
Sun May 30, 2021 8:20 am
Forum: NESemdev
Topic: Cheap Highpass Filter? (just add/subtract and bitshifts)
Replies: 7
Views: 1045

Re: Cheap Highpass Filter? (just add/subtract and bitshifts)

Can the constant 1024 be doubled to cut the corner frequency in half?
by Dwedit
Sat May 29, 2021 7:18 pm
Forum: NESemdev
Topic: Cheap Highpass Filter? (just add/subtract and bitshifts)
Replies: 7
Views: 1045

Cheap Highpass Filter? (just add/subtract and bitshifts)

I remember reading about a really cheap Highpass/DC cancellation filter that used only addition/subtraction and bit shifts. But I can't remember what the formula was, or where I heard about it from. I think emulators used this formula. Does anyone know it?
by Dwedit
Fri May 28, 2021 12:35 pm
Forum: NESdev
Topic: NES dev on retro pc
Replies: 20
Views: 2209

Re: NES dev on retro pc

ASM6 has source code available, you may be able to build it with a C compiler that targets such a system, but I haven't tested it on the 286 with 640K of RAM.

And no, there is no benefit to using an old PC, unless you need to connect peripherals to obsolete buses (Parallel, Serial, ISA slot, etc...)