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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,
; try putting your code as far down as possible, after the function zDecEnd.
; That will make you less likely to run into space shortages from dislocated data alignment.
;
; >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
; Setup defines and macros
; 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): 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 applied 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 affects 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 ; The head of the queue
Queue0: ds.b 1
Queue1: ds.b 1
Queue2: ds.b 1 ; This slot was totally broken in Sonic 1's driver. It's mostly fixed here, but it's still a little broken (see 'zInitMusicPlayback').
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 otherwise)
SpeedUpFlag: ds.b 1
DACEnabled: ds.b 1
MusicBankNumber: ds.b 1
IsPalFlag: ds.b 1 ; Flags if the system is a PAL console
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...
zStack = zMusicData+$800 ; 1B80h
phase zStack
zAbsVar: zVar
zTracksStart: ; This is the beginning of all BGM track memory
zSongDACFMStart:
zSongDAC: zTrack
zSongFMStart:
zSongFM1: zTrack
zSongFM2: zTrack
zSongFM3: zTrack
zSongFM4: zTrack
zSongFM5: zTrack
zSongFM6: zTrack
zSongFMEnd:
zSongDACFMEnd:
zSongPSGStart:
zSongPSG1: zTrack
zSongPSG2: zTrack
zSongPSG3: zTrack
zSongPSGEnd:
zTracksEnd:
zTracksSFXStart:
zSFX_FMStart:
zSFX_FM3: zTrack
zSFX_FM4: zTrack
zSFX_FM5: zTrack
zSFX_FMEnd:
zSFX_PSGStart:
zSFX_PSG1: zTrack
zSFX_PSG2: zTrack
zSFX_PSG3: zTrack
zSFX_PSGEnd:
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
if *>$2000
fatal "Z80 variables are \{*-$2000}h bytes past the end of Z80 RAM!"
endif
dephase
MUSIC_TRACK_COUNT = (zTracksEnd-zTracksStart)/zTrack.len
MUSIC_DAC_FM_TRACK_COUNT = (zSongDACFMEnd-zSongDACFMStart)/zTrack.len
MUSIC_FM_TRACK_COUNT = (zSongFMEnd-zSongFMStart)/zTrack.len
MUSIC_PSG_TRACK_COUNT = (zSongPSGEnd-zSongPSGStart)/zTrack.len
SFX_TRACK_COUNT = (zTracksSFXEnd-zTracksSFXStart)/zTrack.len
SFX_FM_TRACK_COUNT = (zSFX_FMEnd-zSFX_FMStart)/zTrack.len
SFX_PSG_TRACK_COUNT = (zSFX_PSGEnd-zSFX_PSGStart)/zTrack.len
; 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 $8000 byte boundary
bankswitch macro addr68k
if OptimiseDriver=1
; Because why use a and e when you can use h and l?
ld hl,zBankRegister+1 ; +1 so that 6000h becomes 6001h, which is still a valid bankswitch port
.cnt := 0
rept 9
; this is either ld (hl),h or ld (hl),l
db (74h|(((addr68k)&(1<<(15+.cnt)))<>0))
.cnt := (.cnt+1)
endm
else
xor a ; a = 0
ld e,1 ; e = 1
ld hl,zBankRegister
.cnt := 0
rept 9
; this is either ld (hl),a or ld (hl),e
db (73h|((((addr68k)&(1<<(15+.cnt)))==0)<<2))
.cnt := (.cnt+1)
endm
endif
endm
; macro to make a certain error message clearer should you happen to get it...
rsttarget macro {INTLABEL}
if ($&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,zStack
jp zStartDAC
; ---------------------------------------------------------------------------
; zbyte_7:
zPalModeByte:
db 0
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
if OptimiseDriver=0 ; This is redundant: the Z80 is slow enough to not need to worry about this
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
endif
; ||||||||||||||| 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
if OptimiseDriver=0
push af
rst zFMBusyWait ; 'rst' is like 'call' but only works for 8-byte aligned addresses <= 38h
pop af
endif
ld (zYM2612_A0),a
push af
if OptimiseDriver=0
rst zFMBusyWait
endif
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
if OptimiseDriver=0
push af
rst zFMBusyWait
pop af
endif
ld (zYM2612_A1),a
push af
if OptimiseDriver=0
rst zFMBusyWait
endif
ld a,c
ld (zYM2612_D1),a
pop af
ret
; End of function zWriteFMII
; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
org 38h
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
xor a ; Clear 'a'
ld (zDoSFXFlag),a ; Not updating SFX (updating music)
ld ix,zAbsVar ; 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.Queue0)
or (ix+zVar.Queue1)
or (ix+zVar.Queue2) ; This was missing in Sonic 1's driver, breaking the third queue 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,.pal_timer ; If the spindash counter is already 0, jump
dec a ; Decrease the spindash sound playing counter
ld (zSpindashPlayingCounter),a
.pal_timer:
; 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,.not_pal ; If it comes out zero, do nothing
ld hl,zPALUpdTick
dec (hl)
jr nz,.not_pal
ld (hl),5 ; Every 6 frames (0-5) you need to "double update" to sort of keep up
call zUpdateMusic
.not_pal:
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)
if FixDriverBugs
; A bugfix in zUpdateMusic prevents it from returning ix set to a convenient value, so set it explicitly here
ld ix,zTracksSFXStart-zTrack.len
endif
; FM SFX channels
ld b,SFX_FM_TRACK_COUNT ; Only 3 FM channels for SFX (FM3, FM4, FM5)
.fmloop:
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 .fmloop
; PSG SFX channels
ld b,SFX_PSG_TRACK_COUNT ; All PSG channels available
.psgloop:
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 .psgloop
; 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,.dacqueued ; 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
.dacqueued:
; 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 (zDACStartAddress+1),a ; Store into the instruction after zDACStartAddress (self-modifying code)
add a,zDACLenTbl-zDACPtrTbl ; How to offset to length versus pointer
ld (zDACStoreLength+2),a ; Store into the instruction after zDACStoreLength (self-modifying code)
pop af
ld hl,zWriteToDAC
ex (sp),hl ; Jump to zWriteToDAC
; zloc_104
zDACStartAddress:
ld hl,(zDACPtrTbl) ; Self-modified code: sets start address of DAC sample for zWriteToDAC
; zloc_107
zDACStoreLength:
ld de,(zDACLenTbl) ; Self-modified code: sets length of DAC sample for zWriteToDAC
;zloc_10B
zDACStoreDelay:
ld bc,100h ; Self-modified code: From zDACDataStore; 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:
if FixDriverBugs=0
; Calling this function here is bad, because it can cause the
; first note of a newly-started song to be delayed for a frame.
; The vanilla driver resorts to a workaround to prevent such a
; delay from having side-effects, but it's better to just fix
; the problem directly, and move this call to the proper place.
call TempoWait
endif
; 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,MUSIC_FM_TRACK_COUNT ; Loop 6 times (FM)...
.fmloop:
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 .fmloop
ld b,MUSIC_PSG_TRACK_COUNT ; Loop 3 times (PSG)...
.psgloop:
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 .psgloop
if FixDriverBugs=0
; See above. Removing this instruction will cause this
; subroutine to fall-through to TempoWait.
ret
endif
; 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,zAbsVar ; 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,MUSIC_TRACK_COUNT ; Loop for all tracks
.tempoloop:
inc (hl) ; Increasing delay tick counter to target
add hl,de ; Next track...
djnz .tempoloop
ret
; End of function TempoWait
; ---------------------------------------------------------------------------
; zloc_167
zStartDAC:
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 table. 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 (.highnybble+2),a ; store into the instruction after .highnybble (self-modifying code)
ex af,af' ; shadow register 'a' is the 'd' value for 'jman2050' encoding
; zloc_18B
.highnybble:
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 (.lownybble+2),a ; store into the instruction after .lownybble (self-modifying code)
ex af,af' ; shadow register 'a' is the 'd' value for 'jman2050' encoding
; zloc_1A8
.lownybble:
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
; 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)
.sampleloop:
ld a,(hl) ; Get next byte from DAC Track
inc hl ; Move to next position...
cp 0E0h ; Check if is coordination flag
jr c,.notcoord ; Not coord flag? Skip ahead
call zCoordFlag ; Handle coordination flag
jp .sampleloop ; Loop back around...
.notcoord:
or a ; Test 'a' for 80h not set, which is a note duration
jp p,.gotduration ; If note duration, jump ahead (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,.repeatduration ; Is this a duration this time?? If so, jump ahead (only difference is to increment "hl")
; Note followed by 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
.repeatduration:
inc hl ; Goes to next byte (after duration byte)
; zloc_20E
.gotduration:
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 (zDACDataStore+2),a ; store into the following instruction (self-modifying code)
; zloc_22A
zDACDataStore:
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 (zDACStoreDelay+1),a ; store into the instruction after zDACStoreDelay (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,.notegoing ; 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
.notegoing:
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
.noteloop:
ld a,(hl)
inc hl ; Increment track to next byte
cp 0E0h ; Is it a control byte / "coordination flag"?
jr c,.gotnote ; If not, jump over
call zCoordFlag ; Handle coordination flag
jr .noteloop ; Go around, get next byte
.gotnote:
push af
call zFMNoteOff ; Send key off
pop af
or a ; Test 'a' for 80h not set, which is a note duration
jp p,.gotduration ; If duration, jump to .gotduration
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
.gotduration:
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...
if OptimiseDriver
ld d,12*2 ; 12 notes per octave
ld c,0 ; Clear c (will hold octave bits)
.loop:
sub d ; Subtract 1 octave from the note
jr c,.getoctave ; If this is less than zero, we are done
inc c ; One octave up
jr .loop
.getoctave:
add a,d ; Add 1 octave back (so note index is positive)
sla c
sla c
sla c ; Multiply octave value by 8, to get final octave bits
endif
add a,zFrequencies&0FFh
ld (.storefreq+2),a ; Store into the instruction after .storefreq (self-modifying code)
; ld d,a
; adc a,(zFrequencies&0FF00h)>>8
; sub d
; ld (.storefreq+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
.storefreq:
ld de,(zFrequencies) ; Stores frequency into "de"
ld (ix+zTrack.FreqLow),e ; Frequency low byte -> trackPtr + 0Dh
if OptimiseDriver
ld a,d
or c
ld (ix+zTrack.FreqHigh),a ; Frequency high byte -> trackPtr + 0Eh
else
ld (ix+zTrack.FreqHigh),d ; Frequency high byte -> trackPtr + 0Eh
endif
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
.multloop:
djnz .multloop_outer
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
.multloop_outer:
add a,c ; Will multiply duration based on 'b'
jp .multloop
; 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 zUpdateTrack 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,.waitdone ; if zero, go to it!
dec (ix+zTrack.ModulationWait) ; Otherwise, decrement timer
ret ; return if decremented (does NOT return to zUpdateTrack!!)
.waitdone:
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