Search found 311 matches

by Petruza
Sun May 24, 2015 8:31 am
Forum: NESemdev
Topic: Do 2002.7 = 1 and NMI occur at the same time?
Replies: 7
Views: 3401

Do 2002.7 = 1 and NMI occur at the same time?

Is it correct to wait for 262x341* PPU cycles have passed and then set 2002.7 to 1 and immediately start NMI?
Should one of them start earlier? how much?

*: I'm not accounting for the 340 cycle scanline odd frames yet, and this is NTSC only of course.
by Petruza
Mon May 18, 2015 9:02 am
Forum: NESemdev
Topic: Data to pull for drawing pixels
Replies: 5
Views: 3415

Re: Data to pull for drawing pixels

For example, to draw pixel 0: I look at 0x0000 and 0x0008 to get the least significant bits of the color for pixel 0. Yes, that's for pixel 0 of tile 0 of a given pattern table. Then you have to look up the nametable entries or sprites that use that tile, figure out which palette they use from the ...
by Petruza
Tue May 05, 2015 9:06 am
Forum: NESemdev
Topic: Is there an illegal opcodes list with lengths and cycles?
Replies: 8
Views: 2371

Re: Is there an illegal opcodes list with lengths and cycles

rainwarrior wrote:If the instructions aren't implemented, a warning to the user when the first bad opcode is hit at least would let them know that behaviour past this point is not expected to be correct.
Oh yes, totally.
by Petruza
Tue May 05, 2015 7:26 am
Forum: NESemdev
Topic: Is there an illegal opcodes list with lengths and cycles?
Replies: 8
Views: 2371

Re: Is there an illegal opcodes list with lengths and cycles

http://www.oxyron.de/html/opcodes02.html Byte length is determined solely by addressing mode, so... Right, thanks! In your emulator, you should implement this as a toggleable feature to stop/halt the emulator if an invalid opcode is encountered, or to skip them. Good idea. There'd be zero expectati...
by Petruza
Mon May 04, 2015 6:25 pm
Forum: NESemdev
Topic: Is there an illegal opcodes list with lengths and cycles?
Replies: 8
Views: 2371

Is there an illegal opcodes list with lengths and cycles?

Is there an undocumented opcodes list with byte lengths and cycle count? I don't need to know how the actual instructions work or what status flags it affects, as I don't plan to implement any undocumented opcodes, but In the case that an undocumented opcode is found I want my emulator be able to ju...
by Petruza
Mon May 04, 2015 8:12 am
Forum: NESemdev
Topic: Do Mapper 0 games use illegal opcodes? (no, a bit, a lot?)
Replies: 14
Views: 3868

Re: Do Mapper 0 games use illegal opcodes? (no, a bit, a lot

rainwarrior wrote:1. I would highly suspect that they were forbidden in documentation given by Nintendo to licensed developers, and of course, also undocumented.
Is such a documentation available somewhere? Is there any Nintendo official programming reference for the NES?
by Petruza
Sat May 02, 2015 11:57 pm
Forum: NESemdev
Topic: Do Mapper 0 games use illegal opcodes? (no, a bit, a lot?)
Replies: 14
Views: 3868

Do Mapper 0 games use illegal opcodes? (no, a bit, a lot?)

I've compared my emulator's disassembly to nestest's log and fixed every difference until I hit an illegal opcode, of which I haven't implemented any yet. Since my phase 1 goal is making the emulator work with mapper 0 games, I'd like to know if implementing all the illegal codes is a must or if I c...
by Petruza
Thu Apr 30, 2015 7:01 am
Forum: NESdev International
Topic: Comunidad nesdev hispana
Replies: 94
Views: 89937

Re: Comunidad nesdev hispana

Paso a presentarme por aca. Soy Pablo de Argentina y me registre mas que nada para ver si alguien me da una mano con un proyecto que tenemos con un amigo para convertir famiclones de Pal-N a NTSC sin cambiar el ppu, descubrimos que con puentear un pin en los ppu de estos andan a 60hz pero no logram...
by Petruza
Thu Jan 01, 2015 8:29 pm
Forum: NESemdev
Topic: Famicom/NES Remix emulation core?
Replies: 10
Views: 4304

Re: Famicom/NES Remix emulation core?

LocalH, I.m developing an emu in the same line. Have you done something yet? where are you at?
by Petruza
Wed Aug 13, 2014 9:06 am
Forum: NESemdev
Topic: nemulator source code released
Replies: 1
Views: 3246

Re: nemulator source code released

Hi James, I know this is a very old post, but nemulator sources are not anymore on your site, are they available to download anywhere else?
Does anybody else have the source?
I would like to take a look at it.
Thanks!

edit: James told me it's closed source now.
by Petruza
Thu Jun 26, 2014 8:33 pm
Forum: NESemdev
Topic: AND Immediate, opcode $29, takes 2 or 3 cycles?
Replies: 7
Views: 2296

Re: AND Immediate, opcode $29, takes 2 or 3 cycles?

Opcode $29 is not LDA. (It's AND) You're right, I thought of AND but wrote LDA. I have no reason to doubt this favorite page for 6502 instructions: http://www.obelisk.demon.co.uk/6502/reference.html Me neither, in fact I based my CPU emulator on that page. Also, where exactly in FCEUX's source do y...
by Petruza
Thu Jun 26, 2014 4:42 pm
Forum: NESemdev
Topic: AND Immediate, opcode $29, takes 2 or 3 cycles?
Replies: 7
Views: 2296

AND Immediate, opcode $29, takes 2 or 3 cycles?

Marat fayzullin's emulator source code says 2.
FCEUX source code says 3.
I have an old note on my emu source saying Bregalad said it takes 3 cycles.
But according to http://nesdev.com/6502_cpu.txt, all immediates take 2 cycles.

So what is it, 2 or 3?

Edit: it's 2 cycles, not 3.
by Petruza
Thu Jan 23, 2014 11:26 am
Forum: NESdev
Topic: rNES - a NES library for cc65 - version 0.1 released
Replies: 67
Views: 42296

Re: rNES - a NES library for cc65 - version 0.1 released

Hi, it's been around 5 years since I stopped development on rNES, so have that in mind, I barely remember any technical details about it. But some people asked about it since the download links stopped working, so I put it up again in case anyone wants to take a look. The source is a bit of a mess, ...
by Petruza
Fri Nov 25, 2011 5:58 am
Forum: NESdev International
Topic: Comunidad nesdev hispana
Replies: 94
Views: 89937

ah porque las pusieron abajo, pero arriba no creo que quede muy mal.

Image

Sólo una sugerencia.