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 Post subject: Questions
PostPosted: Tue Oct 11, 2005 3:23 pm 

Joined: Thu Sep 15, 2005 9:23 am
Posts: 1194
Location: Behind you with a knife!
Here are some questions that I have. Thanks in advance for answering them.

1. Why is FCE Ultra so highly rated? It has a poor GUI and many bugs. For instance it can't run Clu Clu Land or Spy vs Spy, and they are basic NROM games.

2. Many emulators get a Dr. PC jr. pass in a PPU palette test in NEStress. My emulator gets a NES pass. Since the documentation claims that the NES does not have the palette value passed into the pipe, would it be better for a NES emulator to get a NES pass instead?

3. Since the PAL PPU renders 3.2 pixels every CPU cycle does that mean an extra pixel is rendered every 5 PPU pixels?

4. In NEStress there are 3 sprite tests that everyone fails. Does anyone know what these are for?

5. In Arkanoid it seems that you have an infinite amount of lives. Is this an emulation bug or a bug within the game?

6. Can the memory registers be modified by a different instruction that STx? i.e. ASL 2001h

7. The following is extracted from loopy's scrolling doc;

scanline start (if background and sprites are enabled):
frame start (line 0) (if background and sprites are enabled):

Does scanline start refer to the start of every scanline? Does frame start refer to the dummy scanline, the first scanline, or the start of the VBlank?

8. According to Brad Taylor's document, 2 tiles are prefetched during the HBlank period for the next scanline. The document also says that during the first 256 PPU cc's 32 tiles worth of data is fetched. Shouldn't that be 30 tiles?


 Post subject:
PostPosted: Tue Oct 11, 2005 4:25 pm 
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Joined: Wed Nov 10, 2004 6:47 pm
Posts: 1849
1) It was one of the originals that stood up above the rest... along with being very complete. Nowadays... several other emulators have caught up (and perhaps even surpassed it), but it still has the backing of being around longer than those other emus.. .which is why it's still favored by many.

Personally, I consider it one of the higher-end emus, but it by no means is the end-all of all NES emulators.

2) I believe that on $2007 read, the palette value gets returned, and the mirrored nametable goes into the $2007 read buffer (so if the PPU address is $3F00, the palette color $3F00 is returned, and the nametable byte at $2F00 is put in the read buffer). As far as I can tell... proper NES behavior will give you a Dr PC Jr. return on NEStress -- which is why they say... "don't trust NEStress".

3) I'm not 100% sure what you mean.... but I think the answer you're looking for is yes. Every 1 PAL CPU cycle means 3.2 PPU cycles (note PPU cycles does not necessarily mean pixels!!!!! There are 341 cycles per scanline but only 256 rendered pixels!). After 5 PAL CPU cycles, 16 PPU cycles will have passed. And After 5 NTSC CPU cycles, 15 PPU cycles will have passed. So yeah, I suppose you could think of it as an extra ppu cycle every 5 cpu cycles.

4) No idea... i have similar problems with NEStress as well.

5) Bad dump. There are zillions of bad Arkanoid dumps floating around. Almost as much as SMB.

6) Absolutly. While that's not common for $2xxx or $4xxx registers... several MMC1 games do something like "INC $FFF9" to do a reset write.

7) 'Scanline Start' actually occurs on ppu cycle 257 of the scanline. This is done on EVERY scanline when the PPU is on (including the pre-render scanline). It resets the X scroll for the next scanline.

'Frame Start' actually occurs on cycle 304 of the pre-render scanline.

8) No. 34 tiles are actually loaded for each scanline. You'd need at least 33 because when the fine horizontal scroll is nonzero, you will see part of the 33rd tile. The 34th is never drawn to the screen, however it is still loaded... and I believe MMC2 games (Mike Tyson's Punch Out) use it to CHR swap... so it's important to load it even though it's never drawn.

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