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|
;****************************************************************************
; EntryPoint
; Where the program starts
;****************************************************************************
EntryPoint:
ld sp, RAM_Stack ; Init stack
xor a ; Reset Echo status
ld (RAM_Status), a
ld hl, $7F11 ; Mute PSG
ld (hl), $9F
ld (hl), $BF
ld (hl), $DF
ld (hl), $FF
xor a
ld (RAM_PSGData), a
ld (RAM_PSGData+16), a
ld (RAM_PSGData+32), a
ld (RAM_PSGData+48), a
ld hl, $6000 ; Set default bank
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld ix, $4000 ; YM2612 I/O ports base address
ld iyh, $40
exx ; Init PCM playback status
ld b, $00 ; Not playing
exx
ld (ix+0), $2B ; Disable DAC by default
ld (ix+1), $00
ld e, $7F ; Mute all FM channels
ld a, $40
ld b, 4
.mutefm:
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
inc a
djnz .mutefm
ld (ix+0), $B4 ; Ensure all channels can be heard from both
ld (ix+1), $C0 ; speakers (by default they're mute!)
ld (ix+0), $B5
ld (ix+1), $C0
ld (ix+0), $B6
ld (ix+1), $C0
ld (ix+2), $B4
ld (ix+3), $C0
ld (ix+2), $B5
ld (ix+3), $C0
ld (ix+2), $B6
ld (ix+3), $C0
ld (ix+0), $24 ; Init timers
ld (ix+1), $FE
ld (ix+0), $25
ld (ix+1), $03
ld (ix+0), $26
ld (ix+1), $C9
ld (ix+0), $27
ld (ix+1), $3F
jp IdleLoop ; Go into idle loop
;****************************************************************************
; PollPCM
; Used to update PCM while not idle
;****************************************************************************
PollPCM: macro
ld a, ($4000)
rrca
call c, UpdatePCM
endm
;****************************************************************************
; RunCommand
; Checks which command to run
;----------------------------------------------------------------------------
; To-do: replace with pointer list?
;****************************************************************************
RunCommand:
dec a ; Command $01: load list
jp z, LoadList
dec a ; Command $02: play SFX
jp z, PlaySFX
dec a ; Command $03: stop SFX
jp z, StopSFXCmd
dec a ; Command $04: play BGM
jp z, PlayBGM
dec a ; Command $05: stop BGM
jp z, StopBGMCmd
dec a ; Command $06: resume BGM
jp z, ResumeBGM
dec a ; Command $07: set PCM rate
jp z, SetPCMRate
PollPCM
xor a ; Bad command, ignore >:(
ld (RAM_Command), a
PollPCM
;****************************************************************************
; IdleLoop
; Loop that runs when not processing SFX or BGM
;****************************************************************************
IdleLoop:
ld a, (RAM_Command) ; Look for commands
or a
jr nz, RunCommand
PollPCM ; Poll PCM
ld a, ($4000) ; Tick?
bit 1, a
jr nz, DoTick
bit 0, a ; Poll PCM again
call nz, UpdatePCM ; Not using macro for optimization purposes
jp IdleLoop ; Keep idling
;****************************************************************************
; DoTick
; Called whenever a new tick triggers
;****************************************************************************
DoTick:
ld a, (ix+0)
bit 0, a
call nz, UpdatePCM
ld (ix+0), $27
ld (ix+1), $2F
PollPCM
DoTick_SFX: ; Process SFXs
jp DoTick_SFXSkip
DoTick_SFXSkip:
PollPCM
DoTick_BGM: ; Process BGMs
jp DoTick_BGMSkip
DoTick_BGMSkip:
PollPCM
jp UpdatePSG ; Update PSG envelopes
DoTick_PSGSkip:
PollPCM
jp IdleLoop ; End of subroutine
;****************************************************************************
; BankSwitch
; Switches into a new bank (won't update player status!)
;
; input A .... New bank to switch into
; input HL ... Must be $6000
; breaks ..... AF
;****************************************************************************
BankSwitch: macro
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
ld (hl), h
rrca
ld (hl), a
endm
;****************************************************************************
; LoadList [command $01]
; Loads the pointer list
;****************************************************************************
LoadList:
ld hl, RAM_ComBank ; Get command parameters
ld c, (hl)
inc l
ld e, (hl)
inc l
ld d, (hl)
ex de, hl
xor a ; Command parsed
ld (RAM_Command), a
ld de, RAM_PointerList ; Where the pointer list starts
.loop:
call GetParam ; Get high byte address
ld a, b ; Is it the end of the list?
or a
jp z, .end
ld (de), a ; Store high byte address
inc d
call GetParam ; Get low address byte
ld a, b
ld (de), a
inc d
call GetParam ; Get bank byte
ld a, b
ld (de), a
dec d ; Go for next byte
dec d
inc e
jp .loop
.end:
jp IdleLoop ; End of subroutine
;****************************************************************************
; GetParam
; Subroutine for getting the parameter byte
;****************************************************************************
GetParam:
ld a, (RAM_LastBank) ; Bank switch?
cp c
jp z, .noswitchp
ld a, c
ld (RAM_LastBank), a
push hl
ld hl, $6000
BankSwitch
pop hl
.noswitchp:
ld b, (hl) ; Get volume
inc l ; Get next address
jp nz, .nonewbankp
inc h
jp nz, .nonewbankp
ld h, $80
inc c
.nonewbankp:
ret ; End of subroutine
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