Acmlm's Board - I2 Archive - Rom Hacking - Editing code after tracing it
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d4s
Posts: 246/325 |
Originally posted by Ringodoggie
I mean how do I change an address that is DMA'd to?
a dma transfer is initiated by writing to register $420B.
the individual bits correspond to the dma channels(0-7), eg writing $01 to
$420b will start a dma transfer on channel 0, $06 will start transfers on channels 1 and 2, you get the idea.
each dma channel is configured by writing to registers $43x0-$43x7 (x is the channel number).
the relevant registers for changing the dma transfer source are
$43x2-$43x4 (source adress+bank).
example:
if theres a dma transfer on channel 2 and you want to change the source adress to
$c6:0388 you'd have to write $0388 to register $4322 and $c6 to register $4324.
keep in mind that hdma and dma share the same channels when adding/changing dma transfer channels.
you can only dma from the a-bus to the b-bus (thats the ppu registers) or vice versa, but not from a to a or from b to b, mind you.
that means you can dma from rom to vram, but not from rom to wram, for example.
register $43x1 determines the b-bus target adress.
when writing to vram, it is used in conjunction with register $2116, wich contains the vram target adress.
keep in mind that vram adresses are always divided by 2 because theyre 16bit aligned.
heres how a typical dma transfer looks like:
;**********************************
;in: x,16bit: pointernumber of tilemap
;**********************************
CGIntroDMATileMapToVramBG2:
sep #$20
lda #(:BG2TileMap1+$c0) ;get source bank of tilemaps
sta.w $4304 ;Store the bank of the source data
rep #$30 ;accu/index 16bit
txa ;get number of tilemap
asl ;multiply by 4(each table-entry has 2 bytes adress, 2 bytes length)
asl ;
tax
lda.w Bg2TileMapPTable,x ;get source offset of tilemap
sta.w $4302
ldx.w #$0800
stx.w $2116 ;vram adress $0000
lda.w #$1000
sta.w $4305 ;Store the size of the data block
sep #$20
lda #$80
sta $2115 ;set VRAM transfer mode to word-access, increment by 1
lda #$01 ;Set the DMA mode (word, normal increment)
sta $4300
lda #$18 ;Set the destination register (VRAM gate)
sta $4301
lda #$01 ;Initiate the DMA transfer
sta $420B
rts
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BGNG
Posts: 120/276 |
You might be able to find some useful info by looking up some technical documentation on the subject. Not exactly "change the programming"-esque, but it may provide some useful insight. |
beneficii
Posts: 241/567 |
Probably because I don't trust those programs to write the code into, say, SMB3 the right way, so I simply do it myself.
Now, if I was writing a ROM from scratch, then I would definitely use an assembler.
Originally posted by d4s
Originally posted by beneficii
In FCEUXD, when I trace it, I look through the code I know I'll be editing and plan for what I'll be doing. I then open up Notepad to type my new ASM. Then I open up the ROM in a hex editor and write in the opcodes myself.
manually compiling code is a big time waster and doesnt give you any advantages at all.
ive done it myself, but only for processors that dont have a compiler available (super fx) and only for very, very small amounts of code, like 3 to 4 opcodes.
besides, its nearly impossible to write proper structured and dynamic code that way. why not use wla dx or any other readily-available compiler instead?
Originally posted by Ringodoggie
What about DMA code?
i assume you want to either detect dma transfers or you want to learn how to do them the right way.
try to be more specific with your questions.
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Ringodoggie
Posts: 226/281 |
I mean how do I change an address that is DMA'd to? |
d4s
Posts: 245/325 |
Originally posted by beneficii
In FCEUXD, when I trace it, I look through the code I know I'll be editing and plan for what I'll be doing. I then open up Notepad to type my new ASM. Then I open up the ROM in a hex editor and write in the opcodes myself.
manually compiling code is a big time waster and doesnt give you any advantages at all.
ive done it myself, but only for processors that dont have a compiler available (super fx) and only for very, very small amounts of code, like 3 to 4 opcodes.
besides, its nearly impossible to write proper structured and dynamic code that way. why not use wla dx or any other readily-available compiler instead?
Originally posted by Ringodoggie
What about DMA code?
i assume you want to either detect dma transfers or you want to learn how to do them the right way.
try to be more specific with your questions.
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beneficii
Posts: 240/567 |
Originally posted by Ringodoggie
What about DMA code?
Do you mean sprite-loading code? Remember, I only really know the NES, not the SNES. I was just dropping off advice I thought was general ASM hacking. |
Ringodoggie
Posts: 224/281 |
What about DMA code? |
beneficii
Posts: 239/567 |
In FCEUXD, when I trace it, I look through the code I know I'll be editing and plan for what I'll be doing. I then open up Notepad to type my new ASM. Then I open up the ROM in a hex editor and write in the opcodes myself. |
Ringodoggie
Posts: 222/281 |
In SNES9x Debug, how do I edit code that I trace? Do I disassemble the ROM first? |
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hukka
