Nes
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aprentice
Moderator
Surely I could
If i remember correctly, last time i made an nes emu it ran more commercial than yours >
You should give it a go, im getting kinda lonely being the only one on this forum working on one, im not doing crazy optimizations this time because i want to focus more on accuracy and everyones cpu has a few cores nowadays so it doesnt matter lol
hap
New member
For the PPU area, I don't know if I'm 100% correct at that, but I return the last value on the PPU databus, this includes reading the PPU status register unused bits. So.. if a game reads or writes to a PPU register, I set a variable to the value written/read. If a game reads an undefined PPU location, like $2000, I return that value.
For any other area, it's the CPU databus, simply the high byte of the address read, like reading from $4000 returns $40, reading from $6000-$7FFF if the game doesn't have a RAM chip returns $60-$7F (I think Low G Man relies on that). The unused bits of the game controller register returns part of the previous databus value too, so if a game reads from $4016/$4017, simply OR with $40, Paperboy is uncontrollable otherwise.
For any other area, it's the CPU databus, simply the high byte of the address read, like reading from $4000 returns $40, reading from $6000-$7FFF if the game doesn't have a RAM chip returns $60-$7F (I think Low G Man relies on that). The unused bits of the game controller register returns part of the previous databus value too, so if a game reads from $4016/$4017, simply OR with $40, Paperboy is uncontrollable otherwise.
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aprentice
Moderator
thanks for the info, got almost all sprite and ppu io done, just kind of stuck on 2005h and 2006h, my implamentation is poor since i don't really understand loopys doc. are there any better docs for these registers? I know these registers arent critical to get games running but im gonna need scrolling eventually
hap
New member
loopy's docs are explained by Disch here: http://nesdev.parodius.com/bbs/viewtopic.php?t=664
hey
Yea I understand loopy's doc fine now days, but originally I had no clue, hehe.
Anyhows I can handle $2005/$2006/$2007 fine on the cpu side of things, just when it comes to rendering a scanline... I can't figure out what I'm meant todo with them, and how to update them.
Well all my attempts at implementing tile scrolling and such have had issues, so I dunno :\.
BTW, in loopy's doc, the 1's represent the affected bits.
edit
Ohh, I just remembered that the rom I used for testing scrolling used a mapper that I didn't support. But I didn't realise cause it was working to a point, hehe. Anyhows might have to find another rom for testing scrolling or something, or maybe I already did and don't remember.
another...
Well I read through that forum post, and things make more sense when it comes to rendering now.
Anyhows I see that between rendering each pixel I think it would be possible to change the scroll value and such? so I think I will make an array for each pixel of a scanline, and record the scroll values and such when each pixel is to be drawn (hmm, I guess I'd have to simulate a read from ppu to update the scroll values or whatever between each pixel also), so when it comes to rendering I can still render a complete scanline at a time, and refer to my array for the true scroll values.
Hmm, or maybe I could use some sorta stack instead, I dunno.
cyas
Yea I understand loopy's doc fine now days
, but originally I had no clue, hehe.Anyhows I can handle $2005/$2006/$2007 fine on the cpu side of things, just when it comes to rendering a scanline... I can't figure out what I'm meant todo with them, and how to update them.
Well all my attempts at implementing tile scrolling and such have had issues, so I dunno :\.
BTW, in loopy's doc, the 1's represent the affected bits.
edit
Ohh, I just remembered that the rom I used for testing scrolling used a mapper that I didn't support. But I didn't realise cause it was working to a point, hehe. Anyhows might have to find another rom for testing scrolling or something, or maybe I already did and don't remember.
another...
Well I read through that forum post, and things make more sense when it comes to rendering now
.Anyhows I see that between rendering each pixel I think it would be possible to change the scroll value and such? so I think I will make an array for each pixel of a scanline, and record the scroll values and such when each pixel is to be drawn (hmm, I guess I'd have to simulate a read from ppu to update the scroll values or whatever between each pixel also), so when it comes to rendering I can still render a complete scanline at a time, and refer to my array for the true scroll values.
Hmm, or maybe I could use some sorta stack instead, I dunno.
cyas
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hey
I read in that forum post (and maybe simular things elsewhere) that $2005/$2006/loopyV is constantly updated as the ppu fetches tiles to render.
But it's not very specific about things...
Anyhows I find that there are at least 5 reads from memory to draw a tile. Firstly 1 to read the background tile index, then 2 to read the pattern data, then 1 to read the attribute byte, and finally 1 more to lookup the color.
Hmm, and there could be more depending on whether there are sprites within the scanline/pixel.
So won't all these reads screw things? as for each read $2005/$2006/loopV is incremented by 1.
Another thing I don't get, is where does looking up the name table address and such from $2000 come into play?
cyas
I read in that forum post (and maybe simular things elsewhere) that $2005/$2006/loopyV is constantly updated as the ppu fetches tiles to render.
But it's not very specific about things...
Anyhows I find that there are at least 5 reads from memory to draw a tile. Firstly 1 to read the background tile index, then 2 to read the pattern data, then 1 to read the attribute byte, and finally 1 more to lookup the color.
Hmm, and there could be more depending on whether there are sprites within the scanline/pixel.
So won't all these reads screw things? as for each read $2005/$2006/loopV is incremented by 1.
Another thing I don't get, is where does looking up the name table address and such from $2000 come into play?
cyas
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aprentice
Moderator
ok heres an updated shot from the emu, this is probably the only game that shows this much gfx but hopefully im not far off from commercial
Congratulations :>
I don't think so, I only do emulators when I think there's a need for a new one somewhere. Almost every platform that can do NES well already is. I released my PC-Engine emulator though. Maybe I should post this in that thread no one cared about ;D