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s2.sounddriver.asm
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s2.sounddriver.asm
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; Sonic the Hedgehog 2 disassembled Z80 sound driver
; Disassembled by Xenowhirl for AS
; Additional disassembly work by RAS Oct 2008
; RAS' work merged into SVN by Flamewing
; ---------------------------------------------------------------------------
FixDriverBugs = 0
OptimiseDriver = 0
; ---------------------------------------------------------------------------
; NOTES:
;
; Set your editor's tab width to 8 characters wide for viewing this file.
;
; This code is compressed in the ROM, but you can edit it here as uncompressed
; and it will automatically be assembled and compressed into the correct place
; during the build process.
;
; This Z80 code can use labels and equates defined in the 68k code,
; and the 68k code can use the labels and equates defined in here.
; This is fortunate, as they contain references to each other's addresses.
;
; If you want to add significant amounts of extra code to this driver,
; I suggest putting your code as far down as possible, after the function zloc_12FC.
; That will make you less likely to run into space shortages from dislocated data alignment.
;
; >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
; setup defines and macros and stuff
; Okay, I spent a freakin' weekend trying to figure out this Z80 engine
; (cause I just love it so much ;) ), and this is pretty much everything I've
; got; it's probably about 95% figured out.
; - I didn't do 68K queueing completely... it's in there, I'm just a little fuzzy right now
; I briefly touched the Saxman decoder though I'm not using it; I figured someone
; else can play with that. I think playing music out of ROM is just dandy,
; even if it does require a little post-processing to work. And actually, with
; some tweaks, I think I can get this beast on relative addresses... heheheh
; LOTS of decoding work and relabelling of unknowns! This is a much more complete disasm ;)
; zComRange: @ 1B80h
; +00h -- Priority of current SFX (cleared when 1-up song is playing)
; +01h -- tempo clock
; +02h -- current tempo
; +03h -- Pause/unpause flag: 7Fh for pause; 80h for unpause (set from 68K)
; +04h -- total volume levels to continue decreasing volume before fade out considered complete (starts at 28h, works downward)
; +05h -- delay ticker before next volume decrease
; +06h -- communication value
; +07h -- "DAC is updating" flag (set to FFh until completion of DAC track change)
; +08h -- When NOT set to 80h, 68K request new sound index to play
; +09h -- SFX to Play queue slot
; +0Ah -- Play stereo sound queue slot
; +0Bh -- Unknown SFX Queue slot
; +0Ch -- Address to table of voices
;
; +0Eh -- Set to 80h while fading in (disabling SFX) then 00h
; +0Fh -- Same idea as +05h, except for fade IN
; +10h -- Same idea as +04h, except for fade IN
; +11h -- 80h set indicating 1-up song is playing (stops other sounds)
; +12h -- main tempo value
; +13h -- original tempo for speed shoe restore
; +14h -- Speed shoes flag
; +15h -- If 80h, FM Channel 6 is NOT in use (DAC enabled)
; +16h -- value of which music bank to use (0 for MusicPoint1, $80 for MusicPoint2)
; +17h -- Pal mode flag
;
; ** zTracksStart starts @ +18h
;
; 1B98 base
; Track 1 = DAC
; Then 6 FM
; Then 3 PSG
;
;
; 1B98 = DAC
; 1BC2 = FM 1
; 1BEC = FM 2
; 1C16 = FM 3
; 1C40 = FM 4
; 1C6A = FM 5
; 1C94 = FM 6
; 1CBE = PSG 1
; 1CE8 = PSG 2
; 1D12 = PSG 3 (tone or noise)
;
; 1D3C = SFX FM 3
; 1D66 = SFX FM 4
; 1D90 = SFX FM 5
; 1DBA = SFX PSG 1
; 1DE4 = SFX PSG 2
; 1E0E = SFX PSG 3 (tone or noise)
;
;
zTrack STRUCT DOTS
; "playback control"; bits:
; 1 (02h): seems to be "track is at rest"
; 2 (04h): SFX is overriding this track
; 3 (08h): modulation on
; 4 (10h): do not attack next note
; 7 (80h): track is playing
PlaybackControl: ds.b 1
; "voice control"; bits:
; 2 (04h): If set, bound for part II, otherwise 0 (see zWriteFMIorII)
; -- bit 2 has to do with sending key on/off, which uses this differentiation bit directly
; 7 (80h): PSG Track
VoiceControl: ds.b 1
TempoDivider: ds.b 1 ; timing divisor; 1 = Normal, 2 = Half, 3 = Third...
DataPointerLow: ds.b 1 ; Track's position low byte
DataPointerHigh: ds.b 1 ; Track's position high byte
Transpose: ds.b 1 ; Transpose (from coord flag E9)
Volume: ds.b 1 ; channel volume (only ap plied at voice changes)
AMSFMSPan: ds.b 1 ; Panning / AMS / FMS settings
VoiceIndex: ds.b 1 ; Current voice in use OR current PSG tone
VolFlutter: ds.b 1 ; PSG flutter (dynamically effects PSG volume for decay effects)
StackPointer: ds.b 1 ; "Gosub" stack position offset (starts at 2Ah, i.e. end of track, and each jump decrements by 2)
DurationTimeout: ds.b 1 ; current duration timeout; counting down to zero
SavedDuration: ds.b 1 ; last set duration (if a note follows a note, this is reapplied to 0Bh)
;
; ; 0Dh / 0Eh change a little depending on track -- essentially they hold data relevant to the next note to play
SavedDAC: ; DAC: Next drum to play
FreqLow: ds.b 1 ; FM/PSG: frequency low byte
FreqHigh: ds.b 1 ; FM/PSG: frequency high byte
NoteFillTimeout: ds.b 1 ; Currently set note fill; counts down to zero and then cuts off note
NoteFillMaster: ds.b 1 ; Reset value for current note fill
ModulationPtrLow: ds.b 1 ; low byte of address of current modulation setting
ModulationPtrHigh: ds.b 1 ; high byte of address of current modulation setting
ModulationWait: ds.b 1 ; Wait for ww period of time before modulation starts
ModulationSpeed: ds.b 1 ; Modulation Speed
ModulationDelta: ds.b 1 ; Modulation change per Mod. Step
ModulationSteps: ds.b 1 ; Number of steps in modulation (divided by 2)
ModulationValLow: ds.b 1 ; Current modulation value low byte
ModulationValHigh: ds.b 1 ; Current modulation value high byte
Detune: ds.b 1 ; Set by detune coord flag E1; used to add directly to FM/PSG frequency
VolTLMask: ds.b 1 ; zVolTLMaskTbl value set during voice setting (value based on algorithm indexing zGain table)
PSGNoise: ds.b 1 ; PSG noise setting
VoicePtrLow: ds.b 1 ; low byte of custom voice table (for SFX)
VoicePtrHigh: ds.b 1 ; high byte of custom voice table (for SFX)
TLPtrLow: ds.b 1 ; low byte of where TL bytes of current voice begin (set during voice setting)
TLPtrHigh: ds.b 1 ; high byte of where TL bytes of current voice begin (set during voice setting)
LoopCounters: ds.b $A ; Loop counter index 0
; ... open ...
GoSubStack: ; start of next track, every two bytes below this is a coord flag "gosub" (F8h) return stack
;
; The bytes between +20h and +29h are "open"; starting at +20h and going up are possible loop counters
; (for coord flag F7) while +2Ah going down (never AT 2Ah though) are stacked return addresses going
; down after calling coord flag F8h. Of course, this does mean collisions are possible with either
; or other track memory if you're not careful with these! No range checking is performed!
;
; All tracks are 2Ah bytes long
zTrack ENDSTRUCT
zVar STRUCT DOTS
SFXPriorityVal: ds.b 1
TempoTimeout: ds.b 1
CurrentTempo: ds.b 1 ; Stores current tempo value here
StopMusic: ds.b 1 ; Set to 7Fh to pause music, set to 80h to unpause. Otherwise 00h
FadeOutCounter: ds.b 1
FadeOutDelay: ds.b 1
Communication: ds.b 1 ; Unused byte used to synchronise gameplay events with music
DACUpdating: ds.b 1 ; Set to FFh while DAC is updating, then back to 00h
QueueToPlay: ds.b 1 ; if NOT set to 80h, means new index was requested by 68K
SFXToPlay: ds.b 1 ; When Genesis wants to play "normal" sound, it writes it here
SFXStereoToPlay: ds.b 1 ; When Genesis wants to play alternating stereo sound, it writes it here
SFXUnknown: ds.b 1 ; Unknown type of sound queue, but it's in Genesis code like it was once used
VoiceTblPtr: ds.b 2 ; address of the voices
FadeInFlag: ds.b 1
FadeInDelay: ds.b 1
FadeInCounter: ds.b 1
1upPlaying: ds.b 1
TempoMod: ds.b 1
TempoTurbo: ds.b 1 ; Stores the tempo if speed shoes are acquired (or 7Bh is played anywho)
SpeedUpFlag: ds.b 1
DACEnabled: ds.b 1
MusicBankNumber: ds.b 1
IsPalFlag: ds.b 1 ; I think this flags if system is PAL
zVar ENDSTRUCT
; equates: standard (for Genesis games) addresses in the memory map
zYM2612_A0 = $4000
zYM2612_D0 = $4001
zYM2612_A1 = $4002
zYM2612_D1 = $4003
zBankRegister = $6000
zPSG = $7F11
zROMWindow = $8000
; more equates: addresses specific to this program (besides labelled addresses)
zMusicData = $1380 ; don't change this unless you change all the pointers in the BINCLUDE'd music too...
zComRange = zMusicData+$800 ; 1B80h ; most communication between Z80 and 68k happens in here, among other things (like stack storage)
phase zComRange
zAbsVar: zVar
zTracksStart: ; This is the beginning of all BGM track memory
zSongDAC: zTrack
zSongFM1: zTrack
zSongFM2: zTrack
zSongFM3: zTrack
zSongFM4: zTrack
zSongFM5: zTrack
zSongFM6: zTrack
zSongPSG1: zTrack
zSongPSG2: zTrack
zSongPSG3: zTrack
zTracksEnd:
zTracksSFXStart:
zSFX_FM3: zTrack
zSFX_FM4: zTrack
zSFX_FM5: zTrack
zSFX_PSG1: zTrack
zSFX_PSG2: zTrack
zSFX_PSG3: zTrack
zTracksSFXEnd:
zTracksSaveStart: ; When extra life plays, it backs up a large amount of memory (all track data plus 36 bytes)
zSaveVar: zVar
zSaveSongDAC: zTrack
zSaveSongFM1: zTrack
zSaveSongFM2: zTrack
zSaveSongFM3: zTrack
zSaveSongFM4: zTrack
zSaveSongFM5: zTrack
zSaveSongFM6: zTrack
zSaveSongPSG1: zTrack
zSaveSongPSG2: zTrack
zSaveSongPSG3: zTrack
zTracksSaveEnd:
; see the very end for another set of variables
dephase
; in what I believe is an unfortunate design choice in AS,
; both the phased and unphased PCs must be within the target processor's range,
; which means phase is useless here despite being designed to fix this problem...
; oh well, I set it up to fix this later when processing the .p file
!org 0 ; Z80 code starting at address 0 has special meaning to s2p2bin.exe
CPU Z80UNDOC
listing purecode
; macro to perform a bank switch... after using this,
; the start of zROMWindow points to the start of the given 68k address,
; rounded down to the nearest $8000 byte boundary
bankswitch macro addr68k
xor a ; a = 0
ld e,1 ; e = 1
ld hl,zBankRegister
cnt := 0
rept 9
; this is either ld (hl),a or ld (hl),e
db (73h|((((addr68k)&(1<<(15+cnt)))==0)<<2))
cnt := (cnt+1)
endm
endm
; macro to make a certain error message clearer should you happen to get it...
rsttarget macro {INTLABEL}
if ($&7)||($>38h)
fatal "Function __LABEL__ is at 0\{$}h, but must be at a multiple of 8 bytes <= 38h to be used with the rst instruction."
endif
if "__LABEL__"<>""
__LABEL__ label $
endif
endm
; function to decide whether an offset's full range won't fit in one byte
offsetover1byte function from,maxsize, ((from&0FFh)>(100h-maxsize))
; macro to make sure that ($ & 0FF00h) == (($+maxsize) & 0FF00h)
ensure1byteoffset macro maxsize
if offsetover1byte($,maxsize)
startpad := $
align 100h
if MOMPASS=1
endpad := $
if endpad-startpad>=1h
; warn because otherwise you'd have no clue why you're running out of space so fast
warning "had to insert \{endpad-startpad}h bytes of padding before improperly located data at 0\{startpad}h in Z80 code"
endif
endif
endif
endm
; function to turn a 68k address into a word the Z80 can use to access it,
; assuming the correct bank has been switched to first
zmake68kPtr function addr,zROMWindow+(addr&7FFFh)
; >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
; Z80 'ROM' start:
;zEntryPoint:
di ; disable interrupts
ld sp,zComRange ; sp = zComRange
jp zloc_167
; ---------------------------------------------------------------------------
; zbyte_7:
zPalModeByte:
db 0
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
align 8
;zsub_8
zFMBusyWait: rsttarget
; Performs the annoying task of waiting for the FM to not be busy
ld a,(zYM2612_A0)
add a,a
jr c,zFMBusyWait
ret
; End of function zFMBusyWait
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
align 8
;zsub_10
zWriteFMIorII: rsttarget
bit 2,(ix+zTrack.VoiceControl)
jr z,zWriteFMI
jr zWriteFMII
; End of function zWriteFMIorII
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
align 8
;zsub_18
zWriteFMI: rsttarget
; Write reg/data pair to part I; 'a' is register, 'c' is data
push af
rst zFMBusyWait ; 'rst' is like 'call' but only works for 8-byte aligned addresses <= 38h
pop af
ld (zYM2612_A0),a
push af
rst zFMBusyWait
ld a,c
ld (zYM2612_D0),a
pop af
ret
; End of function zWriteFMI
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
align 8
;zsub_28
zWriteFMII: rsttarget
; Write reg/data pair to part II; 'a' is register, 'c' is data
push af
rst zFMBusyWait
pop af
ld (zYM2612_A1),a
push af
rst zFMBusyWait
ld a,c
ld (zYM2612_D1),a
pop af
ret
; End of function zWriteFMII
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
align 8
zVInt: rsttarget
; This is called every VBLANK (38h is the interrupt entry point,
; and VBLANK is the only one Z80 is hooked up to.)
push af ; Save 'af'
exx ; Effectively backs up 'bc', 'de', and 'hl'
call zBankSwitchToMusic ; Bank switch to the music (depending on which BGM is playing in my version)
xor a ; Clear 'a'
ld (zDoSFXFlag),a ; Not updating SFX (updating music)
ld ix,zComRange ; ix points to zComRange
ld a,(zAbsVar.StopMusic) ; Get pause/unpause flag
or a ; test 'a'
jr z,zUpdateEverything ; If zero, go to zUpdateEverything
call zPauseMusic
jp zUpdateDAC ; Now update the DAC
; ---------------------------------------------------------------------------
;zloc_51
zUpdateEverything:
ld a,(zAbsVar.FadeOutCounter) ; are we fading out?
or a
call nz,zUpdateFadeout ; If so, update that
ld a,(zAbsVar.FadeInFlag) ; are we fading in?
or a
call nz,zUpdateFadeIn ; If so, update that
ld a,(zAbsVar.SFXToPlay) ; zComRange+09h -- play normal sound
or (ix+zVar.SFXStereoToPlay) ; zComRange+0Ah -- play stereo sound (alternating speakers)
or (ix+zVar.SFXUnknown) ; zComRange+0Bh -- "unknown" slot
call nz,zCycleQueue ; If any of those are non-zero, cycle queue
; Apparently if this is 80h, it does not play anything new,
; otherwise it cues up the next play (flag from 68K for new item)
ld a,(zAbsVar.QueueToPlay)
cp 80h
call nz,zPlaySoundByIndex ; If not 80h, we need to play something new!
; Spindash update
ld a,(zSpindashPlayingCounter)
or a
jr z,+ ; if the spindash counter is already 0, branch
dec a ; decrease the spindash sound playing counter
ld (zSpindashPlayingCounter),a
+
; If the system is PAL, then this performs some timing adjustments
; (i.e. you need to update 1.2x as much to keep up the same rate)
ld hl,zPalModeByte ; Get address of zPalModeByte
ld a,(zAbsVar.IsPalFlag) ; Get IsPalFlag -> 'a'
and (hl) ; 'And' them together
jr z,+ ; If it comes out zero, do nothing
ld hl,zPALUpdTick
dec (hl)
jr nz,+
ld (hl),5 ; every 6 frames (0-5) you need to "double update" to sort of keep up
call zUpdateMusic
+
call zUpdateMusic
; Now all of the SFX tracks are updated in a similar manner to "zUpdateMusic"...
bankswitch SoundIndex ; Bank switch to sound effects
ld a,80h
ld (zDoSFXFlag),a ; Set zDoSFXFlag = 80h (updating sound effects)
; FM SFX channels
ld b,(zSFX_PSG1-zSFX_FM3)/zTrack.len ; Only 3 FM channels for SFX (FM3, FM4, FM5)
- push bc
ld de,zTrack.len ; Spacing between tracks
add ix,de ; Next track
bit 7,(ix+zTrack.PlaybackControl) ; Is it playing?
call nz,zFMUpdateTrack ; If it is, go update it
pop bc
djnz -
; PSG SFX channels
ld b,(zTracksSFXEnd-zSFX_PSG1)/zTrack.len ; All PSG channels available
- push bc
ld de,zTrack.len ; Spacing between tracks
add ix,de ; Next track
bit 7,(ix+zTrack.PlaybackControl) ; Is it playing?
call nz,zPSGUpdateTrack ; If it is, go update it
pop bc
djnz -
; Now we update the DAC... this only does anything if there's a new DAC
; sound to be played. This is called after updating the DAC track.
; Otherwise it just mucks with the timing loop, forcing an update.
zUpdateDAC:
bankswitch SndDAC_Start ; Bankswitch to the DAC data
ld a,(zCurDAC) ; Get currently playing DAC sound
or a
jp m,+ ; If one is queued (80h+), go to it!
exx ; Otherwise restore registers from mirror regs
ld b,1 ; b=1 (initial feed to the DAC "djnz" loops, i.e. UPDATE RIGHT AWAY)
pop af
ei ; enable interrupts
ret
+
; If you get here, it's time to start a new DAC sound...
ld a,80h
ex af,af' ;'
ld a,(zCurDAC) ; Get current DAC sound
sub 81h ; Subtract 81h (first DAC index is 81h)
ld (zCurDAC),a ; Store that as current DAC sound
; The following two instructions are dangerous: they discard the upper
; two bits of zCurDAC, meaning you can only have 40h DAC samples.
add a,a
add a,a ; a *= 4 (each DAC entry is a pointer and length, 2+2)
add a,zDACPtrTbl&0FFh ; Get low byte into table -> 'a'
ld (zloc_104+1),a ; store into the instruction after zloc_104 (self-modifying code)
add a,zDACLenTbl-zDACPtrTbl ; How to offset to length versus pointer
ld (zloc_107+2),a ; store into the instruction after zloc_107 (self-modifying code)
pop af
ld hl,zWriteToDAC
ex (sp),hl ; Jump to zWriteToDAC
zloc_104:
ld hl,(zDACPtrTbl) ; "self-modified code" -- sets start address of DAC sample for zWriteToDAC
zloc_107:
ld de,(zDACLenTbl) ; "self-modified code" -- sets length of DAC sample for zWriteToDAC
zloc_10B:
ld bc,100h ; "self-modified code" -- From zloc_22A; sets b=1 (the 100h part of it) UPDATE RIGHT AWAY and c="data rate delay" for this DAC sample, the future 'b' setting
ei ; enable interrupts
ret
; End of function zVInt
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
; Updates all tracks; queues notes and durations!
;zsub_110
zUpdateMusic:
call TempoWait ; This is a tempo waiting function
; DAC updates
ld a,0FFh
ld (zAbsVar.DACUpdating),a ; Store FFh to DACUpdating
ld ix,zTracksStart ; Point "ix" to zTracksStart
bit 7,(ix+zTrack.PlaybackControl) ; Is bit 7 (80h) set on playback control byte? (means "is playing")
call nz,zDACUpdateTrack ; If so, zDACUpdateTrack
xor a ; Clear A
ld (zAbsVar.DACUpdating),a ; Store 0 to DACUpdating
ld b,(zSongPSG1-zSongFM1)/zTrack.len ; Loop 6 times (FM)...
- push bc
ld de,zTrack.len ; Space between tracks
add ix,de ; Go to next track
bit 7,(ix+zTrack.PlaybackControl) ; Is bit 7 (80h) set on playback control byte? (means "is playing")
call nz,zFMUpdateTrack ; If so...
pop bc
djnz -
ld b,(zTracksEnd-zSongPSG1)/zTrack.len ; Loop 3 times (PSG)...
- push bc
ld de,zTrack.len ; Space between tracks
add ix,de ; Go to next track
bit 7,(ix+zTrack.PlaybackControl) ; Is this track playing?
call nz,zPSGUpdateTrack ; If so...
pop bc
djnz -
ret
; End of function zUpdateMusic
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_14C
TempoWait:
; Tempo works as divisions of the 60Hz clock (there is a fix supplied for
; PAL that "kind of" keeps it on track.) Every time the internal music clock
; overflows, it will update. So a tempo of 80h will update every other
; frame, or 30 times a second.
ld ix,zComRange ; ix points to zComRange
ld a,(ix+zVar.CurrentTempo) ; tempo value
add a,(ix+zVar.TempoTimeout) ; Adds previous value to
ld (ix+zVar.TempoTimeout),a ; Store this as new
ret c ; If addition overflowed (answer greater than FFh), return
; So if adding tempo value did NOT overflow, then we add 1 to all durations
ld hl,zTracksStart+zTrack.DurationTimeout ; Start at first track's delay counter (counting up to delay)
ld de,zTrack.len ; Offset between tracks
ld b,(zTracksEnd-zTracksStart)/zTrack.len ; Loop for all tracks
- inc (hl) ; Increasing delay tick counter to target
add hl,de ; Next track...
djnz -
ret
; End of function TempoWait
; ---------------------------------------------------------------------------
zloc_167:
im 1 ; set interrupt mode 1
call zClearTrackPlaybackMem
ei ; enable interrupts
ld iy,zDACDecodeTbl
ld de,0
; This controls the update rate for the DAC...
; My speculation for the rate at which the DAC updates:
; Z80 clock = 3.57954MHz = 3579540Hz (not sure?)
; zWaitLoop (immediately below) is waiting for someone to set
; 'de' (length of DAC sample) to non-zero
; The DAC code is sync'ed with VBLANK somehow, but I haven't quite got that
; one figure out yet ... tests on emulator seem to confirm it though.
; Next, there are "djnz" loops which do busy-waits. (Two of them, which is
; where the '2' comes from in my guess equation.) The DACMasterPlaylist
; appears to use '1' as the lowest input value to these functions. (Which,
; given the djnz, would be the fastest possible value.)
; The rate seems to be calculated by 3579540Hz / (60Hz + (speed * 4)) / 2
; This "waitLoop" waits if the DAC has no data, or else it drops out!
; zloc_174:
zWaitLoop:
ld a,d
or e
jr z,zWaitLoop ; As long as 'de' (length of sample) = 0, wait...
; 'hl' is the pointer to the sample, 'de' is the length of the sample,
; and 'iy' points to the translation table; let's go...
; The "djnz $" loops control the playback rate of the DAC
; (the higher the 'b' value, the slower it will play)
; As for the actual encoding of the data, it is described by jman2050:
; "As for how the data is compressed, lemme explain that real quick:
; First, it is a lossy compression. So if you recompress a PCM sample this way,
; you will lose precision in data. Anyway, what happens is that each compressed data
; is separated into nybbles (1 4-bit section of a byte). This first nybble of data is
; read, and used as an index to a table containing the following data:
; 0,1,2,4,8,$10,$20,$40,$80,$FF,$FE,$FC,$F8,$F0,$E0,$C0." [zDACDecodeTbl / zbyte_1B3]
; "So if the nybble were equal to F, it'd extract $C0 from the tale. If it were 8,
; it would extract $80 from the table. ... Anyway, there is also another byte of data
; that we'll call 'd'. At the start of decompression, d is $80. What happens is that d
; is then added to the data extracted from the table using the nybble. So if the nybble
; were 4, the 8 would be extracted from the table, then added to d, which is $80,
; resulting in $88. This result is then put back into d, then fed into the YM2612 for
; processing. Then the next nybble is read, the data is extracted from the table, then
; is added to d (remember, d is now changed because of the previous operation), then is
; put back into d, then is fed into the YM2612. This process is repeated until the number
; of bytes as defined in the table above are read and decompressed."
; In our case, the so-called 'd' value is shadow register 'a'
zWriteToDAC:
djnz $ ; Busy wait for specific amount of time in 'b'
di ; disable interrupts (while updating DAC)
ld a,2Ah ; DAC port
ld (zYM2612_A0),a ; Set DAC port register
ld a,(hl) ; Get next DAC byte
rlca
rlca
rlca
rlca
and 0Fh ; UPPER 4-bit offset into zDACDecodeTbl
ld (zloc_18B+2),a ; store into the instruction after zloc_18B (self-modifying code)
ex af,af' ; shadow register 'a' is the 'd' value for 'jman2050' encoding
zloc_18B:
add a,(iy+0) ; Get byte from zDACDecodeTbl (self-modified to proper index)
ld (zYM2612_D0),a ; Write this byte to the DAC
ex af,af' ; back to regular registers
ld b,c ; reload 'b' with wait value
ei ; enable interrupts (done updating DAC, busy waiting for next update)
djnz $ ; Busy wait for specific amount of time in 'b'
di ; disable interrupts (while updating DAC)
push af
pop af
ld a,2Ah ; DAC port
ld (zYM2612_A0),a ; Set DAC port register
ld b,c ; reload 'b' with wait value
ld a,(hl) ; Get next DAC byte
inc hl ; Next byte in DAC stream...
dec de ; One less byte
and 0Fh ; LOWER 4-bit offset into zDACDecodeTbl
ld (zloc_1A8+2),a ; store into the instruction after zloc_1A8 (self-modifying code)
ex af,af' ; shadow register 'a' is the 'd' value for 'jman2050' encoding
zloc_1A8:
add a,(iy+0) ; Get byte from zDACDecodeTbl (self-modified to proper index)
ld (zYM2612_D0),a ; Write this byte to the DAC
ex af,af' ; back to regular registers
ei ; enable interrupts (done updating DAC, busy waiting for next update)
jp zWaitLoop ; Back to the wait loop; if there's more DAC to write, we come back down again!
; ---------------------------------------------------------------------------
; 'jman2050' DAC decode lookup table
ensure1byteoffset 10h
;zbyte_1B3
zDACDecodeTbl:
db 0, 1, 2, 4, 8, 10h, 20h, 40h
db 80h, -1, -2, -4, -8, -10h, -20h, -40h
; The following two tables are used for when an SFX terminates
; its track to properly restore the music track it temporarily took
; over. Note that an important rule here is that no SFX may use
; DAC, FM Channel 1, FM Channel 2, or FM Channel 6, period.
; Thus there's also only SFX tracks starting at FM Channel 3.
; The zeroes appear after FM 3 because it calculates the offsets into
; these tables by their channel assignment, where between Channel 3
; and Channel 4 there is a gap numerically.
ensure1byteoffset 10h
;zbyte_1C3
zMusicTrackOffs:
; These are offsets to different music tracks starting with FM3
dw zSongFM3, 0000h, zSongFM4, zSongFM5 ; FM3, 0, FM4, FM5
dw zSongPSG1, zSongPSG2, zSongPSG3, zSongPSG3 ; PSG1, PSG2, PSG3, PSG3 (noise alternate)
ensure1byteoffset 10h
;zbyte_1D3
zSFXTrackOffs:
; These are offsets to different sound effect tracks starting with FM3
dw zSFX_FM3, 0000h, zSFX_FM4, zSFX_FM5 ; FM3, 0, FM4, FM5
dw zSFX_PSG1, zSFX_PSG2, zSFX_PSG3, zSFX_PSG3 ; PSG1, PSG2, PSG3, PSG3 (noise alternate)
; ---------------------------------------------------------------------------
zDACUpdateTrack:
dec (ix+zTrack.DurationTimeout) ; Subtract 1 from (zTracksStart+0Bh) [Track 1's delay start]
ret nz ; Return if not zero yet
ld l,(ix+zTrack.DataPointerLow) ; Low byte of DAC track current address (zTracksStart+3)
ld h,(ix+zTrack.DataPointerHigh) ; High byte of DAC track current address (zTracksStart+4)
- ld a,(hl) ; Get next byte from DAC Track
inc hl ; Move to next position...
cp 0E0h ; Check if is coordination flag
jr c,+ ; Not coord flag? Skip to '+'
call zCoordFlag ; Handle coordination flag
jp - ; Loop back around...
+
or a ; Test 'a' for 80h not set, which is a note duration
jp p,zloc_20E ; If note duration, jump to zloc_20E (note that "hl" is already incremented)
ld (ix+zTrack.SavedDAC),a ; This is a note; store it here
ld a,(hl) ; Get next byte...
or a ; Test 'a' for 80h not set, which is a note duration
jp p,zloc_20D ; Is this a duration this time?? If so, jump to zloc_20D (only difference is to increment "hl")
; Note followed a note... apparently recycles the previous duration
ld a,(ix+zTrack.SavedDuration) ; Current DAC note ticker goal value -> 'a'
ld (ix+zTrack.DurationTimeout),a ; Use it again
jr zDACAfterDur ; Jump to after duration subroutine...
; ---------------------------------------------------------------------------
zloc_20D:
inc hl ; Goes to next byte (after duration byte)
zloc_20E:
call zSetDuration
;zloc_211
zDACAfterDur:
ld (ix+zTrack.DataPointerLow),l ; Stores "hl" to the DAC track pointer memory
ld (ix+zTrack.DataPointerHigh),h
bit 2,(ix+zTrack.PlaybackControl) ; Is SFX overriding this track?
ret nz ; If so, we're done
ld a,(ix+zTrack.SavedDAC) ; Check next note to play
cp 80h ; Is it a rest?
ret z ; If so, quit
sub 81h ; Otherwise, transform note into an index... (we're selecting which drum to play!)
add a,a ; Multiply by 2...
add a,zDACMasterPlaylist&0FFh ; Offset into list
ld (zloc_22A+2),a ; store into the instruction after zloc_22A (self-modifying code)
zloc_22A:
ld bc,(zDACMasterPlaylist) ; Load appropriate drum info -> bc
ld a,c ; DAC sample number (81h base) -> 'a'
ld (zCurDAC),a ; Store current DAC sound to play
ld a,b ; Data rate delay -> 'b'
ld (zloc_10B+1),a ; store into the instruction after zloc_10B (self-modifying code)
ret
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_237
zFMUpdateTrack:
dec (ix+zTrack.DurationTimeout) ; Decrement duration
jr nz,+ ; If not time-out yet, go do updates only
res 4,(ix+zTrack.PlaybackControl) ; When duration over, clear "do not attack" bit 4 (0x10) of track's play control
call zFMDoNext ; Handle coordination flags, get next note and duration
call zFMPrepareNote ; Prepares to play next note
call zFMNoteOn ; Actually key it (if allowed)
call zDoModulation ; Update modulation (if modulation doesn't change, we do not return here)
jp zFMUpdateFreq ; Applies frequency update from modulation
+
call zNoteFillUpdate ; Applies "note fill" (time until cut-off); NOTE: Will not return here if "note fill" expires
call zDoModulation ; Update modulation (if modulation doesn't change, we do not return here)
jp zFMUpdateFreq ; Applies frequency update from modulation
; End of function zFMUpdateTrack
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_258
zFMDoNext:
ld l,(ix+zTrack.DataPointerLow) ; Load track position low byte
ld h,(ix+zTrack.DataPointerHigh) ; Load track position high byte
res 1,(ix+zTrack.PlaybackControl) ; Clear bit 1 (02h) "track is rest" from track
- ld a,(hl)
inc hl ; Increment track to next byte
cp 0E0h ; Is it a control byte / "coordination flag"?
jr c,+ ; If not, jump over
call zCoordFlag ; Handle coordination flag
jr - ; Go around, get next byte
+
push af
call zFMNoteOff ; Send key off
pop af
or a ; Test 'a' for 80h not set, which is a note duration
jp p,+ ; If duration, jump to '+'
call zFMSetFreq ; Otherwise, this is a note; call zFMSetFreq
ld a,(hl) ; Get next byte
or a ; Test 'a' for 80h set, which is a note
jp m,zFinishTrackUpdate ; If this is a note, jump to zFinishTrackUpdate
inc hl ; Otherwise, go to next byte; a duration
+
call zSetDuration
jp zFinishTrackUpdate ; Either way, jumping to zFinishTrackUpdate...
; End of function zFMDoNext
; ---------------------------------------------------------------------------
; zloc_285:
;zGetFrequency
zFMSetFreq:
; 'a' holds a note to get frequency for
sub 80h
jr z,zFMDoRest ; If this is a rest, jump to zFMDoRest
add a,(ix+zTrack.Transpose) ; Add current channel transpose (coord flag E9)
add a,a ; Offset into Frequency table...
add a,zFrequencies&0FFh
ld (zloc_292+2),a ; store into the instruction after zloc_292 (self-modifying code)
; ld d,a
; adc a,(zFrequencies&0FF00h)>>8
; sub d
; ld (zloc_292+3),a ; this is how you could store the high byte of the pointer too (unnecessary if it's in the right range)
zloc_292:
ld de,(zFrequencies) ; Stores frequency into "de"
ld (ix+zTrack.FreqLow),e ; Frequency low byte -> trackPtr + 0Dh
ld (ix+zTrack.FreqHigh),d ; Frequency high byte -> trackPtr + 0Eh
ret
; ---------------------------------------------------------------------------
;zloc_29D
zFMDoRest:
set 1,(ix+zTrack.PlaybackControl) ; Set bit 1 (track is at rest)
xor a ; Clear 'a'
ld (ix+zTrack.FreqLow),a ; Zero out FM Frequency
ld (ix+zTrack.FreqHigh),a ; Zero out FM Frequency
ret
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_2A9
zSetDuration:
ld c,a ; 'a' = current duration
ld b,(ix+zTrack.TempoDivider) ; Divisor; causes multiplication of duration for every number higher than 1
- djnz +
ld (ix+zTrack.SavedDuration),a ; Store new duration into ticker goal of this track (this is reused if a note follows a note without a new duration)
ld (ix+zTrack.DurationTimeout),a ; Sets it on ticker (counts to zero)
ret
+
add a,c ; Will multiply duration based on 'b'
jp -
; End of function zSetDuration
; ---------------------------------------------------------------------------
;zloc_2BA
zFinishTrackUpdate:
; Common finish-up routine used by FM or PSG
ld (ix+zTrack.DataPointerLow),l ; Stores "hl" to the track pointer memory
ld (ix+zTrack.DataPointerHigh),h
ld a,(ix+zTrack.SavedDuration) ; Last set duration
ld (ix+zTrack.DurationTimeout),a ; ... put into ticker
bit 4,(ix+zTrack.PlaybackControl) ; Is bit 4 (10h) "do not attack next note" set on playback?
ret nz ; If so, quit
ld a,(ix+zTrack.NoteFillMaster) ; Master "note fill" value -> a
ld (ix+zTrack.NoteFillTimeout),a ; Reset 0Fh "note fill" value to master
ld (ix+zTrack.VolFlutter),0 ; Reset PSG flutter byte
bit 3,(ix+zTrack.PlaybackControl) ; is modulation turned on?
ret z ; if not, quit
ld l,(ix+zTrack.ModulationPtrLow) ; Otherwise, get address of modulation setting
ld h,(ix+zTrack.ModulationPtrHigh)
jp zSetModulation ; ... and go do it!
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_2E3
zNoteFillUpdate:
ld a,(ix+zTrack.NoteFillTimeout) ; Get current note fill value
or a
ret z ; If zero, return!
dec (ix+zTrack.NoteFillTimeout) ; Decrement note fill
ret nz ; If not zero, return
set 1,(ix+zTrack.PlaybackControl) ; Set bit 1 (track is at rest)
pop de ; return address -> 'de' (will not return to z*UpdateTrack function!!)
bit 7,(ix+zTrack.VoiceControl) ; Is this a PSG track?
jp nz,zPSGNoteOff ; If so, jump to zPSGNoteOff
jp zFMNoteOff ; Else, jump to zFMNoteOff
; End of function zNoteFillUpdate
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
;zsub_2FB
zDoModulation:
pop de ; keep return address -> de (MAY not return to caller)
bit 1,(ix+zTrack.PlaybackControl) ; Is "track in rest"?
ret nz ; If so, quit
bit 3,(ix+zTrack.PlaybackControl) ; Is modulation on?
ret z ; If not, quit
ld a,(ix+zTrack.ModulationWait) ; 'ww' period of time before modulation starts
or a
jr z,+ ; if zero, go to it!
dec (ix+zTrack.ModulationWait) ; Otherwise, decrement timer
ret ; return if decremented (does NOT return to z*UpdateTrack!!)
+
dec (ix+zTrack.ModulationSpeed) ; Decrement modulation speed counter
ret nz ; Return if not yet zero
ld l,(ix+zTrack.ModulationPtrLow)
ld h,(ix+zTrack.ModulationPtrHigh) ; 'hl' points to modulation setting
inc hl ; skip passed 'ww' period of time
ld a,(hl) ; Get modulation speed
ld (ix+zTrack.ModulationSpeed),a ; Restore speed counter
ld a,(ix+zTrack.ModulationSteps) ; Get number of steps in modulation
or a
jr nz,+ ; If not zero, skip to '+'
; If steps have reached zero...
inc hl ; passed mod speed
inc hl ; passed mod change per mod step
ld a,(hl) ; get number of steps in modulation
ld (ix+zTrack.ModulationSteps),a ; restore modulation steps
ld a,(ix+zTrack.ModulationDelta) ; get modulation change per mod step
neg ; flip it negative
ld (ix+zTrack.ModulationDelta),a ; store negated value
ret
+
dec (ix+zTrack.ModulationSteps) ; Decrement the step
ld l,(ix+zTrack.ModulationValLow)
ld h,(ix+zTrack.ModulationValHigh) ; Get 16-bit modulation value
; This is a 16-bit sign extension for 'bc'
if OptimiseDriver
ld a,(ix+zTrack.ModulationDelta) ; Get current modulation change per step -> 'a'
ld c,a
rla ; Carry contains sign of delta
sbc a,a ; a = 0 or -1 if carry is 0 or 1
ld b,a ; bc = sign extension of delta
else
ld b,0
ld c,(ix+zTrack.ModulationDelta) ; Get current modulation change per step -> 'c'
bit 7,c
jp z,+
ld b,0FFh ; Sign extend if negative
+
endif
add hl,bc ; Add to current modulation value
ld (ix+zTrack.ModulationValLow),l
ld (ix+zTrack.ModulationValHigh),h ; Store new 16-bit modulation value
ld c,(ix+zTrack.FreqLow) ; frequency low byte -> c
ld b,(ix+zTrack.FreqHigh) ; frequency high byte -> b
add hl,bc ; Add modulation value
ex de,hl
jp (hl) ; WILL return to z*UpdateTrack
; End of function zDoModulation
; ---------------------------------------------------------------------------
; This the note -> frequency setting lookup
; the same array is found at $729CE in Sonic 1, and at $C9C44 in Ristar
; zword_359:
ensure1byteoffset 8Ch
zPSGFrequencies:
dw 356h, 326h, 2F9h, 2CEh, 2A5h, 280h, 25Ch, 23Ah
dw 21Ah, 1FBh, 1DFh, 1C4h, 1ABh, 193h, 17Dh, 167h
dw 153h, 140h, 12Eh, 11Dh, 10Dh, 0FEh, 0EFh, 0E2h
dw 0D6h, 0C9h, 0BEh, 0B4h, 0A9h, 0A0h, 97h, 8Fh
dw 87h, 7Fh, 78h, 71h, 6Bh, 65h, 5Fh, 5Ah
dw 55h, 50h, 4Bh, 47h, 43h, 40h, 3Ch, 39h
dw 36h, 33h, 30h, 2Dh, 2Bh, 28h, 26h, 24h
dw 22h, 20h, 1Fh, 1Dh, 1Bh, 1Ah, 18h, 17h
dw 16h, 15h, 13h, 12h, 11h, 0
; ---------------------------------------------------------------------------
;zloc_3E5
zFMPrepareNote:
bit 1,(ix+zTrack.PlaybackControl) ; Is track in rest?
ret nz ; If so, quit
ld e,(ix+zTrack.FreqLow) ; Get frequency low
ld d,(ix+zTrack.FreqHigh) ; Get frequency high
ld a,d
or e
jp z,zloc_4C5 ; If de == 0, go to zloc_4C5
;zloc_3F5
zFMUpdateFreq:
bit 2,(ix+zTrack.PlaybackControl) ; Is SFX overriding this track?
ret nz ; If so, quit!
; This is a 16-bit sign extension of (ix+19h)
if OptimiseDriver
ld a,(ix+zTrack.Detune) ; Get detune value
ld l,a
rla ; Carry contains sign of detune
sbc a,a ; a = 0 or -1 if carry is 0 or 1
ld h,a ; hl = sign extension of detune
else
ld h,0 ; h = 0
ld l,(ix+zTrack.Detune) ; Get detune value
bit 7,l ; Did prior value have 80h set?
jr z,+ ; If not, skip next step
ld h,0FFh ; h = FFh
+
endif
add hl,de ; Alter frequency just a tad
ld c,h ; Upper part of frequency as data to FM ('c')
ld a,(ix+zTrack.VoiceControl) ; "voice control" byte -> 'a'
and 3 ; Strip to only channel assignment
add a,0A4h ; Change to proper register
rst zWriteFMIorII ; Write it!
ld c,l ; lower part of frequency
sub 4 ; A0h+ register
rst zWriteFMIorII ; Write it!
ret