Difference between revisions of "Fix the SEGA Sound"
From Sonic Retro
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Let's fix a problem that causes a great deal of pain to anyone adding code to Sonic 1: The SEGA sound. | Let's fix a problem that causes a great deal of pain to anyone adding code to Sonic 1: The SEGA sound. | ||
| − | So go to Sound_E1, and replace this: | + | So go to ''Sound_E1'', and replace this: |
<asm>Sound_E1: ; XREF: Sound_ExIndex | <asm>Sound_E1: ; XREF: Sound_ExIndex | ||
move.b #$88,($A01FFF).l | move.b #$88,($A01FFF).l | ||
| Line 17: | Line 17: | ||
rts</asm> | rts</asm> | ||
| − | + | With this: | |
<asm>Sound_E1: | <asm>Sound_E1: | ||
lea (SegaPCM).l,a2 ; Load the SEGA PCM sample into a2. It's important that we use a2 since a0 and a1 are going to be used up ahead when reading the joypad ports | lea (SegaPCM).l,a2 ; Load the SEGA PCM sample into a2. It's important that we use a2 since a0 and a1 are going to be used up ahead when reading the joypad ports | ||
| Line 38: | Line 38: | ||
rts</asm> | rts</asm> | ||
| − | If using the SVN community disassembly | + | == SVN disassembly continuation == |
| + | If you are using the SVN community disassembly you need to do the following steps as well. | ||
| + | |||
| + | The line: | ||
<asm>jsr (Joypad_Read).w</asm> | <asm>jsr (Joypad_Read).w</asm> | ||
| − | + | Needs to be changed to: | |
<asm>jsr (ReadJoypads).w</asm> | <asm>jsr (ReadJoypads).w</asm> | ||
| − | + | Or else you'll get an error when building. However, the SEGA sound may play slowly for some reason. To fix this (or at least circumvent it) you can edit this line: | |
| − | |||
| − | To fix this (or at least circumvent it) you can | ||
<asm>move.w #$14,d0 ; Write the pitch ($14 in this case) to d0</asm> | <asm>move.w #$14,d0 ; Write the pitch ($14 in this case) to d0</asm> | ||
| − | + | Change the #$14 value to any other value (try it with ''#$2'' or ''#$3''). If this value is high, the pitch gets lower, and viceversa. Tweak it to your taste. | |
| − | |||
[[Category:SCHG How-tos|Fix the SEGA Sound]] | [[Category:SCHG How-tos|Fix the SEGA Sound]] | ||
Revision as of 15:51, 21 November 2009
(Original guide by Puto)
Let's fix a problem that causes a great deal of pain to anyone adding code to Sonic 1: The SEGA sound.
So go to Sound_E1, and replace this: <asm>Sound_E1: ; XREF: Sound_ExIndex move.b #$88,($A01FFF).l move.w #0,($A11100).l ; start the Z80 move.w #$11,d1 loc_71FC0: move.w #-1,d0 loc_71FC4: nop dbf d0,loc_71FC4 dbf d1,loc_71FC0 addq.w #4,sp rts</asm>
With this: <asm>Sound_E1: lea (SegaPCM).l,a2 ; Load the SEGA PCM sample into a2. It's important that we use a2 since a0 and a1 are going to be used up ahead when reading the joypad ports move.l #$6978,d3 ; Load the size of the SEGA PCM sample into d3 move.b #$2A,($A04000).l ; $A04000 = $2A -> Write to DAC channel PlayPCM_Loop: move.b (a2)+,($A04001).l ; Write the PCM data (contained in a2) to $A04001 (YM2612 register D0) move.w #$14,d0 ; Write the pitch ($14 in this case) to d0 dbf d0,* ; Decrement d0; jump to itself if not 0. (for pitch control, avoids playing the sample too fast) sub.l #1,d3 ; Subtract 1 from the PCM sample size beq.s return_PlayPCM ; If d3 = 0, we finished playing the PCM sample, so stop playing, leave this loop, and unfreeze the 68K lea ($FFFFF604).w,a0 ; address where JoyPad states are written lea ($A10003).l,a1 ; address where JoyPad states are read from jsr (Joypad_Read).w ; Read only the first joypad port. It's important that we do NOT do the two ports, we don't have the cycles for that btst #7,($FFFFF604).w ; Check for Start button bne.s return_PlayPCM ; If start is pressed, stop playing, leave this loop, and unfreeze the 68K bra.s PlayPCM_Loop ; Otherwise, continue playing PCM sample return_PlayPCM: addq.w #4,sp rts</asm>
SVN disassembly continuation
If you are using the SVN community disassembly you need to do the following steps as well.
The line: <asm>jsr (Joypad_Read).w</asm> Needs to be changed to: <asm>jsr (ReadJoypads).w</asm> Or else you'll get an error when building. However, the SEGA sound may play slowly for some reason. To fix this (or at least circumvent it) you can edit this line: <asm>move.w #$14,d0 ; Write the pitch ($14 in this case) to d0</asm> Change the #$14 value to any other value (try it with #$2 or #$3). If this value is high, the pitch gets lower, and viceversa. Tweak it to your taste.