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Author Topic: TLP and FCEUXDSP Questions  (Read 1 times)
Roth
Guest
« on: March 22, 2008, 09:23:47 am »
If I view an NES ROM in TLP, and there is mainly CHR viewable with very little "garbage" data, is it possible that the PRG is compressed? Also, if I use the nametable viewer in FCEUXDSP, and the tiles in the viewer look extremely different, can it also be assumed that those background graphics are compressed? Thanks for any insight.
KingMike
Guest
« Reply #1 on: March 22, 2008, 01:07:36 pm »
PRG cannot be compressed. Data in CHR *ROM* cannot be compressed. However, if the graphics are stored in the PRG ROM they can be compressed.
It is possible for some games to store non-graphics data in CHR-ROM and transfer it to CPU RAM.
(the Super Mario Bros. title screen is probably the best known example of this)
If I remember, TLP actually hides the PRG ROM if it detects an NES game that uses PRG and CHR, as they would not be able to store graphics data in PRG (well, they could STORE it, but wouldn't be able to USE it Tongue).
(though I've heard of some pirate mapper that had both CHR-ROM and CHR-RAM, but I suppose that's beside the point)
Roth
Guest
« Reply #2 on: March 22, 2008, 02:13:44 pm »
Quote from: KingMike on March 22, 2008, 01:07:36 pm
PRG cannot be compressed. Data in CHR *ROM* cannot be compressed. However, if the graphics are stored in the PRG ROM they can be compressed.
It is possible for some games to store non-graphics data in CHR-ROM and transfer it to CPU RAM.
(the Super Mario Bros. title screen is probably the best known example of this)
If I remember, TLP actually hides the PRG ROM if it detects an NES game that uses PRG and CHR, as they would not be able to store graphics data in PRG (well, they could STORE it, but wouldn't be able to USE it Tongue).
(though I've heard of some pirate mapper that had both CHR-ROM and CHR-RAM, but I suppose that's beside the point)

Whoa, I didn't know that CHR-ROM data couldn't be compressed. As an aside, what is the reason that it can't be compressed?
Karatorian
Guest
« Reply #3 on: March 23, 2008, 07:30:06 am »
CHR-ROM cannot be compressed because it's accessed directly by the PPU, which wants it uncompressed. If it was compressed, the PPU would read it as though it wasn't and it'd display as garbage.
Roth
Guest
« Reply #4 on: March 23, 2008, 12:12:19 pm »
Alright, thanks for the explanation : )

I'm currently using Parasyte's doc to lead me in the right direction of finding compression routines. I also plan on checking out this doc by Jay, though I haven't even peaked inside the file yet. Let me know if there are any other docs that I'm not seeing that could be helpful.
Parasyte
Guest
« Reply #5 on: April 01, 2008, 06:49:58 pm »
I'm not sure what you mean by "PRG cannot be compressed ..." Of course it can. That's why we have projects like this and this and this.
Karatorian
Guest
« Reply #6 on: April 02, 2008, 07:58:01 pm »
I think what he meant was that you cannot compress executeable code in PRG-ROM. Which, of course, itsn't strictly true, but due to the relatively small ammount of RAM in the NES, I doubt anyone would bother. Hmm, can you run code in SRAM? Sounds like a fun little project. He he he.
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