Search found 1851 matches

by Quietust
Sat Feb 04, 2023 12:55 pm
Forum: NESemdev
Topic: is nestest infallible?
Replies: 5
Views: 217

Re: is nestest infallible?

My advice would be to start looking here for other CPU test programs - nestest is known to not cover certain types of errors, and some of Blargg's individual CPU tests are more thorough.
by Quietust
Sat Feb 04, 2023 8:19 am
Forum: NESemdev
Topic: APU Emulation
Replies: 5
Views: 252

Re: APU Emulation

The CPU's clock is divided into two phases, each one running at half speed, and those phases are used to run most of the APU. Some operations are driven by the first phase while other operations are driven by the second phase, and this is what results in the "half APU cycles" in various pl...
by Quietust
Fri Feb 03, 2023 5:39 pm
Forum: NESemdev
Topic: scanline test happen exception
Replies: 1
Views: 231

Re: scanline test happen exception

Based on your screenshot and some experiments I just did, it looks like your emulation of Sprite DMA (i.e. handling writes to $4014) isn't consuming the correct number of cycles - once the STA instruction finishes, it needs to consume an additional 512 cycles (since it's performing 256 reads and 256...
by Quietust
Wed Jan 11, 2023 5:23 pm
Forum: NESemdev
Topic: Nestest Accumulator missmatch
Replies: 4
Views: 344

Re: Nestest Accumulator missmatch

realoS wrote: Wed Jan 11, 2023 9:20 am This is because the Lda instruction loads a value from $0180 (a stack adress) which i verified in the debugger is zero at the time of execution.
But it shouldn't be zero, because at address $CE06 (which is a PHA instruction) it gets set to #$33 (because A=$33 and SP=$80).
by Quietust
Sun Jan 08, 2023 1:22 pm
Forum: phpBB Issues
Topic: Weird smiley in some thread title
Replies: 9
Views: 748

Re: Weird smiley in some thread title

Drag wrote: Wed Jan 04, 2023 4:23 pm B) That thread was posted without using the UI at posting.php, when you click the [new thread] button.
Combined with the rather peculiar thread title, it's probably worth keeping an eye on that user's account to make sure it doesn't turn out to be yet another sleeper spambot.
by Quietust
Fri Dec 30, 2022 5:56 pm
Forum: NESdev
Topic: Game Genie sound pitch shifting, possible? (Question)
Replies: 21
Views: 747

Re: Game Genie sound pitch shifting, possible? (Question)

I can definitely tell the difference just by hearing the Pal version on an NTSC system uncompared, maybe it's because i know the Mega Man 1 and 2 soundtrack very well but the second it started playing it sounded off, funny as i saw a list online that stated both Mega Man 1 and 2 were exactly the sa...
by Quietust
Fri Dec 30, 2022 10:15 am
Forum: NESdev
Topic: Game Genie sound pitch shifting, possible? (Question)
Replies: 21
Views: 747

Re: Game Genie sound pitch shifting, possible? (Question)

I'm mainly referring to Mega Man and Mega Man 2 here, exactly the same as all other versions except the pitch of the music, even the speed is the same. I think your emulator is misconfigured and is running the games in NTSC mode - when I run them in PAL mode, the music plays back in the correct key...
by Quietust
Thu Dec 15, 2022 4:13 pm
Forum: Newbie Help Center
Topic: Crazy project by newbie, what can go wrong?
Replies: 4
Views: 501

Re: Crazy project by newbie, what can go wrong?

There's exactly two instructions that you could stuff the data bus with to keep the CPU busy until you can override it. They are both jumps. If you stuffed the data bus with constant "$40", the 2A03 would see that as "JMP $4040" and as long as it kept fetching $4040 the address ...
by Quietust
Sat Oct 29, 2022 9:22 am
Forum: NESemdev
Topic: I'm creating a NES emulator.
Replies: 34
Views: 4128

Re: I'm creating a NES emulator.

Well, my friend, the log from Donkey Kong appears to be the right one. I've tested thru VB's debugger, and it appears that the latest called opcode $B1 at address $F215 is LDA, and it uses the IndirectY addressing mode to add register Y to the next PC. That's not how indirect addressing works. The ...
by Quietust
Sat Oct 29, 2022 6:29 am
Forum: NESemdev
Topic: I'm creating a NES emulator.
Replies: 34
Views: 4128

Re: I'm creating a NES emulator.

Thanks! It was a bug with the relative addressing mode. This is now fixed. I have other issues with the JSR instruction. In Super Mario Bros. ROM, and other ROMs, it's calling the JSR instruction, and then the PC register lands somewhere else, leading to unknown opcode errors. Here's a piece of the...
by Quietust
Sat Oct 29, 2022 4:43 am
Forum: NESemdev
Topic: I'm creating a NES emulator.
Replies: 34
Views: 4128

Re: I'm creating a NES emulator.

However, when it's about running SMB or cpu_dummy_reads, after ~120.000 cycles, my emulator starts finding unknown opcodes. I don't know if there are missing ones, or if the PC register is messed up because of wrong mem reads. But here is a log of the latest 8192 called opcodes by my emulator befor...
by Quietust
Sun Oct 23, 2022 5:46 am
Forum: Newbie Help Center
Topic: when can i change the palette?
Replies: 12
Views: 1163

Re: when can i change the palette?

You can only update the palette while the PPU is not busy rendering the screen, so that only leaves you two options: 1. Update it during VBLANK (along with your other VRAM updates). 2. Disable rendering mid-screen, perform the update, then re-enable rendering. The second technique is generally only ...
by Quietust
Sun Oct 23, 2022 5:35 am
Forum: NESemdev
Topic: I'm creating a NES emulator.
Replies: 34
Views: 4128

Re: I'm creating a NES emulator.

You should probably start by adding a CPU trace log of some sort - each time it executes an instruction, write a line to a text file indicating the exact details of that instruction (i.e. the address, the opcode bytes, a text representation of the instruction, and the contents of all CPU registers a...
by Quietust
Sun Oct 09, 2022 6:05 am
Forum: NES Hardware and Flash Equipment
Topic: Help collecting pictures of CPU and PPU packages
Replies: 72
Views: 4789

Re: Help collecting pictures of CPU and PPU packages

It's interesting how one of them has that middle column of characters blocked off with a single box. Also, there appear to be faint characters before the 7s (looks like a 6) and the Ds (looks like a C or G). Each column represents a layer during the fabrication process - 2 is Diffusion, the invisib...
by Quietust
Fri Oct 07, 2022 4:50 pm
Forum: NESemdev
Topic: I'm creating a NES emulator.
Replies: 34
Views: 4128

Re: I'm creating a NES emulator.

I have yet another question, I don't know when the PPU redraws a scanline on screen, is it like every 30 instructions executed? Plus I saw that even while the PPU draws a scanline, it can execute a single CPU instruction. Is it linked to the VBlank instruction, or NMI interruption, or something lik...