HDMA? - Board 2

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Main - ROM Hacking - HDMA?

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cory21391

Posted on 08-07-07 06:57 PM

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Well, I read 2 or 3 different HDMA tutorials and it seemed simple enough and I thought I unserstood it. But, I guess not... I wanted to test a gradient hdma that changed color 0 per scanline (like it seems DKC does for jungle levels.) Anyways, I jsl-ed from before the title screen fades in to an hdma sub-routine and it just makes color 0 pink. I don't know what I'm doing wrong and could use some help.

compiled smc:
http://www.mediafire.com/?6po4me1du12

hdma sub-routine:
http://www.mediafire.com/?2flufzjjtxs

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blackhole89

Posted on 08-07-07 06:59 PM

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Could you dump the code here in a [code] tag? The uploader page produces JavaScript errors on my end for some reason (on top of doing nothing)...

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cory21391

Posted on 08-07-07 07:05 PM (rev. 2 of 08-07-07 07:06 PM)

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weird, mediafire's never caused me problems before... how about I just post a screen of the 'hdma' in game and the code.

screen with all layers on:

screen where I turned all layers off:

CODE:

;===============
;HDMA
;===============
hdma:

  stz $4300 ;HDMA transfer settings
  lda #$21
  sta $4301 ;sets destination to $2121, CGRAM selection
  ldx #hdmatable0
  stx $4302 ;sets source offset
  lda #:hdmatable0
  sta $4304 ;sets source bank

  stz $4310 ;HDMA transfer settings
  lda #$22
  sta $4311 ;sets destination to $2122, CGRAM write
  ldx #hdmatable1
  stx $4312 ;sets source offset
  lda #:hdmatable1
  sta $4314 ;sets source bank

  lda #$03
  sta $420C ;enables HDMA transfer through channels 0 and 1

  rts

;===============
;HDMA TABLE
;===============
hdmatable0:
  .db 2
    .db $00
  .db 3
    .db $00
  .db 3
    .db $00
  .db 4
    .db $00
  .db 4
    .db $00
  .db 0

hdmatable1:
  .db 2
    .dw $0017
  .db 3
    .dw $001A
  .db 3
    .dw $001C
  .db 4
    .dw $001F
  .db 4
    .dw $085F
  .db 0

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MathOnNapkins

Posted on 08-07-07 07:37 PM (rev. 2 of 08-07-07 07:43 PM)

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register 43x0 from Anomie's register doc

            ttt  = Transfer Mode.
            000 => 1 register write once             (1 byte:  p               )
            001 => 2 registers write once            (2 bytes: p, p+1          )
            010 => 1 register write twice            (2 bytes: p, p            )
            011 => 2 registers write twice each      (4 bytes: p, p,   p+1, p+1)
            100 => 4 registers write once            (4 bytes: p, p+1, p+2, p+3)
            101 => 2 registers write twice alternate (4 bytes: p, p+1, p,   p+1)
            110 => 1 register write twice            (2 bytes: p, p            )
            111 => 2 registers write twice each      (4 bytes: p, p,   p+1, p+1)

The problem here is that you are trying to write a byte for each step of the first transfer on channel 0 and trying to write two bytes every step of the second transfer

You need to do

LDA #$02
STA $4310

That *should* fix it. Let me know how it goes

edit: by the way, I do a transfer similar to this and i only use one HDMA channel. I use transfer mode 011 (3) which writes to $2121 twice then $2122 twice. So it effectively writes the color address twice then writes the whole color using only one table. Yes it's wasteful to write that address twice, but on the other hand, it is also wasteful to have the master cycle overhead of using 2 hdma transfers rather than 1, ne?

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cory21391

Posted on 08-07-07 08:43 PM

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ah, i get it... I knew it was something simple i overlooked because when reading the 2 or 3 tutorials, the basic premise for hdma seemed so simple compared to the general complexity i previously associated it with. well, since I have to use the public library for internet (for now, getting the internet back!!)

Anyways, the computers here deny access to the command prompt so I can't check it until I go back home. But thanks

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