DFADL.ASM

;
;             H   H  EEEEE  RRRR    AAA   DDDD     V   V   222 
;             H   H  E      R   R  A   A  D   D    V   V  2   2
;             HHHHH  EEEEE  RRRR   AAAAA  D   D    V   V     2 
;             H   H  E      R  R   A   A  D   D     V V    2   
;             H   H  EEEEE  R   R  A   A  DDDD       V    22222
;
;  HERAD Source Code recreated from MegaRace (DOS)'s "DFADL.HSQ" AdLib music driver
;  Original code written by Rémi Herbulot with design notes from Stéphane Picq
;  
;  Reverse-engineered and reconstructed source code by SynaMax
;  RE work started back in 2016, source code rewrite completed May 6th, 2024
;
;  DFADL = AdLib card driver (port 388)
;  DFADP = Sound Blaster driver (port 220)
;  "DF" refers to MegaRace's working title, "Drive Fractalus"
;
;  Special thanks to Binarymaster and Jepael for their help
;
;  For more info on HERAD visit: https://www.vgmpf.com/Wiki/index.php/HERAD
;
;  This code targets UASM, you can use the following terminal prompt to build the driver:
;
;; uasm32 -bin -Fl"listing.txt" -Fo "dfadl.bin" dfadl.asm
;
; ---------------------------------------------------------------------------
;
;  HERAD first appeared in the 1992 DOS game, Dune and would be reused in later
;  Cryo titles like KGB/Conspiracy and lastly, MegaRace.  MegaRace's driver differs
;  from the earlier Dune version with the introduction of a drum map mode that makes
;  it much easier to sequence one-shot percussion instruments.  One draw back is that
;  the fade in/out routines from Dune have been disabled here.
;
;  HERAD stands out from other contemporary AdLib music drivers at the time, thanks to
;  the use of instrument macros that give an expressive quality to the OPL2's output.
;
;  By using the velocity of a MIDI note or using a MIDI Aftertouch event, several parameters
;  of the OPL2 can be controlled, creating complex and sophisticated sound design unheard
;  in other PC games at the time.
;
; ---------------------------------------------------------------------------

	.model tiny

	.code
	
; ---------------------------------------------------------------------------
; Constants
TrackNum	equ	9                ; 9 tracks, one for each OPL2 channel
AllTrackPtrs	equ	TrackNum*2       ; 2 bytes for each of the 9 MIDI tracks current pointers
MidiTickValue	equ	96               ; HERAD uses 96 MIDI ticks per 4-bar measure (or 24 PPQN)
SlideCenter	equ	64               ; Slide range center, just like the MIDI Standard

; Song Constants

sLoopStart	equ	2Ah
sLoopEnd	equ	2Ch
sLoopCount	equ	2Eh
sSpeed		equ	30h

; Instrument Chunk offsets and constants
InstSize	equ	28h              ; The size of one instrument chunk

;  0x00 is the Instrument "Mode"
iDrumMode	equ	0FFh             ; FF = DrumMap, any other mode value is regular FM instrument
;  0x01 appears to be metadata, possibly an Instrument ID number

iM_KSL		equ	2                ; Modulator Key scaling level
iM_Multiple	equ	3                ; Modulator Frequency multiplier
iFeedback	equ	4                ; Feedback
iM_Attack	equ	5                ; Modulator Attack
iM_Sus		equ	6                ; Modulator Sustain
iM_EG		equ	7                ; Modulator Envelope gain
iM_Decay	equ	8                ; Modulator Decay
iM_Rel		equ	9                ; Modulator Release
iM_Level	equ	0Ah              ; Modulator Output Level
iM_AM		equ	0Bh              ; Modulator Amplitude modulation (Tremolo)
iM_Vib		equ	0Ch              ; Modulator Frequency Vibrato
iM_KSR		equ	0Dh              ; Modulator Key scaling/envelope rate

iConnector	equ	0Eh              ; Connector

iC_KSL		equ	0Fh              ; Carrier Key scaling level
iC_Multiple	equ	10h              ; Carrier Frequency multiplier
iPanning	equ	11h              ; Panning (OPL3)
iC_Attack	equ	12h              ; Carrier Attack
iC_Sus		equ	13h              ; Carrier Sustain
iC_EG		equ	14h              ; Carrier Envelope gain
iC_Decay	equ	15h              ; Carrier Decay
iC_Rel		equ	16h              ; Carrier Release
iC_Level	equ	17h              ; Carrier Output Level
iC_AM		equ	18h              ; Carrier Amplitude modulation (Trem
iC_Vib		equ	19h              ; Carrier Frequency Vibrato
iC_KSR		equ	1Ah              ; Carrier Key scaling/envelope rate

; HERAD Instrument Macros start here
iX_FBScaleAFT	equ	1Bh              ; Feedback Scaling - Aftertouch

iM_Wave		equ	1Ch              ; Modulator Waveform Select
iC_Wave		equ	1Dh              ; Carrier Waveform Select

iX_MLevelScale	equ	1Eh              ; Modulator Output Level Scaling - Velocity
iX_CLevelScale	equ	1Fh              ; Carrier Output Level Scaling - Velocity

iX_FBScaleVEL	equ	20h              ; Feedback Scaling - Velocity
iX_SlideTrans	equ	21h              ; Pitch Slide Range Flag / Transpose bytes

iX_SlideDurRange equ	23h              ; Pitch Slide Duration / Pitch Slide Range bytes

; 25h is unused

iX_MLevelScaleAFT equ	26h              ; Modulator Output Level Scaling - Aftertouch
iX_CLevelScaleAFT equ	27h              ; Carrier Output Level Scaling - Aftertouch 

;; End of Instrument offsets	

; ---------------------------------------------------------------------------
;; For debugging purposes
;; (Adds blank space at the beginning to make the symbol addresses match up with the absolute addresses)

		;org	0
		;db 256 dup(0)

; ---------------------------------------------------------------------------
;; "DFADP.HSQ" HERAD driver starts at address 0x100 and is usually loaded
;; into memory at 406B:0100.  Music data is found at 4119:0000
;;
;; For "DFADL.HSQ", the music driver is located at address 3B08:0100, music data at 3BB6:0000
	
		org	100h
	
		jmp	DriverInit      ; 3B08:0100
; ---------------------------------------------------------------------------
		jmp	GetSongData     ; 3B08:0103 (Starts music playback, music data gets loaded before this is called)
; ---------------------------------------------------------------------------
		jmp	ShutUp          ; 3B08:0106 (ShutUp, kills all music playback with NoteOffs)
; ---------------------------------------------------------------------------
		jmp	ChangeSong      ; 3B08:0109 (I don't think this gets called)
; ---------------------------------------------------------------------------
		jmp	StopDriver      ; 3B08:010C (Called when game shuts down)
; ---------------------------------------------------------------------------
		jmp	SongPlay        ; 3B08:010F (This is more like a timer that decreases the byte at 0x11E if the SongFlag at 0x19A is non-zero. The game is constantly spamming this even when music isn't playing)
; ---------------------------------------------------------------------------
		jmp	TimerFF         ; 3B08:0112 (Called at the end of initialization)
; ---------------------------------------------------------------------------

SizeOffset	dw      0               ;; This is referenced a lot to parse the song file's header (it is always 2)

SongSegment	dw      0
SongSizeOffset:
SongFileSize	dw      0
SongSegment2	dw      0

SongSpeed	dw      0
MeasureCount	dw      0
MIDITickCount	dw      0
SongPlayCount	dw      0

; ---------------------------------------------------------------------------

EventPointerTable:

; 06CF = NoteOff (80)
; 065D = NoteOn (90)
; 08E5 = Polyphonic Aftertouch (A0)
; 08E5 = Control Mode Change (B0)
; 05D2 = Program Change (C0)
; 072E = Aftertouch (D0)
; 07DD = Pitch Bend (E0)
; 06F5 = End of Track (FF)

		dw      NoteOff_80
		dw      NoteOn_90
		dw      GetChMidiDelay
		dw      GetChMidiDelay
		dw      InstChange_C0
		dw      Aftertouch_D0
		dw      PitchBend_E0
		dw      EndofTrack_FF

; ---------------------------------------------------------------------------

OPLRegTable:
		db      0, 3, 1, 4, 2, 5, 8, 0Bh, 9, 0Ch, 0Ah, 0Dh, 10h, 13h
		db      11h, 14h, 12h, 15h
FreqTable:      
		dw      157h, 16Ch, 181h, 198h, 1B1h, 1CBh, 1E6h, 203h, 222h
                dw      243h, 266h, 28Ah
FNumRegisters:
		dw      9 dup(157h)

OPLPortTable:
		db      0, 1, 2, 8, 9, 0Ah, 10h, 11h, 12h

FineBendTable:
		db      3, 4, 5, 0Bh, 0Ch, 0Dh, 13h, 14h, 15h
unk_BendTable:
		db      13h, 15h, 15h, 17h, 19h, 1Ah, 1Bh, 1Dh, 1Fh, 21h, 23h, 24h, 25h
CoarseBendTable:
		db      0, 5, 0Ah, 0Fh, 14h, 0, 6, 0Ch, 12h, 18h

SongFlag        db      0
ChangeSongFlag  db      0
		
EEx19C		db      0               ;; Originally 0EEh in DFADP
EEx19D		db      0               ;; Originally 0EEh in DFADP
EEx19E		db      0               ;; Originally 0EEh in DFADP

BitTimer	dw      1

End_1A1:	nop                     ;; Possibly a marker to denote the start of the driver internals

; ------------------------ M U S I C  R A M ---------------------------------
;; Underscore in front of label name denotes driver internals
;; The org instructions are not needed unless there's a label that requires it
;; Each of these arrays are 18 bytes in length (2 bytes x 9 tracks)

;Current Midi Event Delay Counter (0x1A2-0x1B3)
;
; counts down until next event 

;		org	1A2h
_MidiEventDelay:

;MIDI Track Position (0x1B4-0x1C5)
;
; counts up until reaching the track end 

;		org	1B4h
_MidiTrackPos	equ	12h

;MIDI Track Start Address (0x1C6-0x1D7)
;
; Absolute address in music file, rather than relative address in music file header 

		org	1C6h
_MidiTrackStart:
_MidiTrackStartPos equ	24h

;List of MIDI tracks using drum keymap instrument (0x1D8-0x1E9)
;
; If MIDI track uses keymap instrument, the absolute offset of the instrument in the music file will be used.
; If the instrument changes back to a normal instrument, the value zeros out. 

;		org	1D8h
_MidiDrumMapPtr equ	36h	

;Current Instrument (first byte) / MIDI Pitch (second byte) (0x1EA-0x1FB)
;
; The pitch here is after any transpose macros have been applied. Also, if the keymap instrument is used,
; the first byte will display the instrument(s) that are actually being played. If no instrument or note data exist,
; the values will be 0xFF/0x00 respectively. NoteOffs are enabled by setting the highest bit to 1 in the pitch byte. 

		org	1EAh
_MidiInstOffset:
_MidiCurInst	equ	48h
_MidiCurPitch	equ	49h

;Pitch Slide Range Flag (first byte) / Root Note Transpose (second byte) for each MIDI track (0x1FC-0x20D)

;		org	1FCh
_XSlideRangeFlag equ	5Ah
_XRootNoteTrans equ	5Bh

;Pitch Slide Duration Counter (first byte) / Pitch Slide Duration (second byte) for each MIDI track (0x20E-0x21F)
;
; The Pitch Slide Counter starts at the value assigned by the second byte. 

		org	20Eh
_XSlideDurOffset:
_XSlideDurCount equ	6Ch
_XSlideDuration equ	6Dh

;Pitch Slide Counter (first byte) / Pitch Slide Range (second byte) for each MIDI track (0x220-0x231)
;
; The Pitch Slide Counter starts at 0x40 (unless it is transposed) and either goes up or down depending on Pitch Slide Range value. 

		org	220h
_XSlideCounter equ	7Eh
_XSlideRange   equ	7Fh

;Modulator Output Level Scaling (first byte) / Carrier Output Level Scaling (Second byte) (0x232-0x243)
;
; These values are taken from the current instrument. 

		org	232h
_FMOutputScaling equ	90h

;Modulator Output Level (first byte) / Carrier Output Level (Second byte) (0x244-0x255)
;
; These values are taken from the current instrument. 

		org	244h
_FMOutputOffset:
_FMOutputLevel	equ	0A2h

;Modulator Output Level Register (first byte) / Carrier Output Level Register (Second byte) (0x256-0x267)
;
; These are the final register values that are sent to the OPL chip. 

		org	256h
_FMOutputRegister equ	0B4h

;Panning/Feedback/Connector Register Value (0x268-0x279)

		org	268h
_FMFeedbackRegister equ 0C6h

;Loop MIDI Delay Values (0x27A-0x28B)
;
; These are the values that the MIDI delay counters load when the song loops. 

		org	27Ah
_LoopMidiEventDelay equ 0D8h

;Loop Start Absolute Address for each MIDI track (0x28C-0x29D)
;
; Loads after the song passes the loop beginning measure. 
		org	28Ch
_LoopMidiStartPtr:

; ---------------------------------------------------------------------------

                org     2C2h

Terminator	db	0
HSQ             dw	5348h
HSQEND          db	51h
PortNum:        ;; Sound Blaster 220h port number is not needed for AdLib driver

; =============== S U B R O U T I N E =======================================

GrabHSQ:           
                push    ss
                pop     es                    ; ES is 0FD9
                mov     si, bp                ; SI is 418A

LoadFileName: 
                lods    word ptr es:[si]      ; Load the string word at 0FD9:418A.  The value should be 4AFD
                ;add     ax,0x0002            ; Add 2 to 4AFD, which gives us 4AFF
		;;;;;;;;;;;;;;;
		db      05h        ;; UASM doesn't use the 05 opcode for ADD.  After several tries,
		dw      0002h      ;; I'm left with no choice but to put this in to match up with the original HERAD driver
		;;;;;;;;;;;;;;;
                mov     di, ax                ; 0FD9:4AFF is the offset for the string "NEWSAN.HSQ"
                push    cx
                mov     cx, 9                 ; put 9 in CX
                mov     al, 2Eh ; '.'         ; place a period in the low byte of AX
                repne scasb                   ; stop when you encounter the period of the filename.  DI is going to be offset for the "H" in HSQ extension.
                pop     cx
                jnz     short LoadFileLOOP
                mov     ax, word ptr cs:HSQ   ; grab the "HSQ" (or in this case 5348) at 3B08:02C3 (0x1C3) and place it in AX
                stosw                         ; go to the end of NEWSAN.HSQ string.
                mov     al, byte ptr cs:HSQEND ; grab "Q" from "HSQ" at 3B08:02C5 and place it in AX's low byte
                stosb

LoadFileLOOP:                         
                loop    LoadFileName
                retn


; ---------------------------------------------------------------------------

DriverInit:
;		and	ax, 0FFFh
;		jz	short OPLStartUp
;		mov	word ptr cs:PortNum, ax	; grab port number 0220	from [02C6]

OPLStartUp:
		call    GrabHSQ
		mov     ax, 2001h             ; Enable Waveform Select at OPL register 01
		call    ChipWrite             ; Write to OPL2
		mov     ax, 0BDh              ; Disable Percussion Mode
		call    ChipWrite             ; Write to OPL2
		mov     ax, 4008h             ; Enable NOTE-SEL at OPL register 08
		call    ChipWrite             ; Write to OPL2
		push    cs
		call    near ptr ShutUp
;		mov     bx, 0F00h
		mov     bx, 500h              ; Different value for DFADL
		retf
		

; =============== S U B	R O U T	I N E =======================================


ShutUp:		
		pushf                         ; clear eflags
		cli                           ; clear IF flag in EFLAGS
		call    KeyOffAll
		xor     ax, ax                ; clear AX
		mov     cs:SongFlag, al       ; write zero to SongFlag
		popf
		retf                          ; And the driver has stopped!

CreateEEE:                                    ; These "EE" bytes are exclusive to the "DFADP" Sound Blaster HERAD driver
		push    bx
;		push    dx
;		shr     al, 1                 ; The value in AX before this starts is 78E6
;		shr     al, 1
;		shr     al, 1
;		mov     dx, ax                ; move 781C to DX
;		mov     bx, 0F078h            ; place F078 in BX
;		cmp     ah, bl                ; compare the low byte of BX with the high byte of AX.
;		jbe     short EEE1
;		mov     ah, bl
;		
;EEE1:           
;		xor     al, al                ; zero out AX's low byte
;		div     bh                    ; divide AX by BX's high byte.  The answer should be 80
;		mul     dl                    ; AX (80) x DL (1C) = E0
;		xchg    ah, dh                ; DX:781C and AX:0E00 now become AX:0E1C and DX:7800
;		sub     ah, bh                ; 0E - F0 = 88
;		neg     ah                    ; two's compliment of 88 = 78
;		cmp     ah, bl                ; compare the two 78s
;		jbe     short EEE2            ; if AX is the incorrect value, continue, otherwise jump
;		mov     ah, bl                ; if AX isn't right, correct it by making it 7800
;		
;EEE2:           
;		xor     al, al                ; zero out AX's low byte (it was already zero though)
;		div     bh                    ; divide 7800 with F0 = 80
;		mul     dl                    ; 80 x 1C = E00
;		shr     ax, 1
;		shr     ax, 1
;		shr     ax, 1
;		shr     ax, 1                 ; now AX is E0
;		mov     ah, dh                ; AX is now EE0
;		and     ax, 0FF0h
;		or      al, ah                ; AX is now EEE
;		pop     dx
		not     al
		shr     al, 1
		shr     al, 1
		mov     ah, al
		mul     ah
		mov     bl, 3Fh
		div     bl
		
		pop     bx
		retn
		
TimerFF:
		call    CreateEEE
		mov     cs:EEx19E, al         ; write EE at 0x9E
		mov     cs:EEx19D, al         ; write EE at 0x9D
		mov     cs:BitTimer, 0FFFFh   ; write FFFF at 0x9F
		retf
		
StopDriver:
		push    ax
		mov     ax, bx
		call    CreateEEE
		mov     cs:EEx19D, al         ; Zero out that middle EE
		pop     ax                    ; value is 12C...don't know what this is
		mov     bx, 0FFFFh            ; BX = FFFF
		;cmp    ax, 60h               ; compare with 60
		;;
		db      3Dh
		dw      60h
		;;
		jb      short StopSongFlag    ; jump if below
		mov     bx, 0AAAAh
		cmp     ax, 0C0h
		jb      short StopSongFlag
		mov     bx, 8888h
		cmp     ax, 180h
		jb      short StopSongFlag
		mov     bx, 8080h
		cmp     ax, 300h
		jb      short StopSongFlag
		xor     bl, bl

StopSongFlag:
		mov     cs:BitTimer, bx       ; write either FFFF, AAAA, 8888, or 8080 to the BitTimer
		mov     al, cs:SongFlag       ; move the SongFlag to AX's low byte
		or      al, al
		jns     short StopDriverEnd
		or      al, 40h               ; turn that 80 into a C0
		mov     cs:SongFlag, al       ; write C0 to SongFlag!

StopDriverEnd:
		retf
; ---------------------------------------------------------------------------

ChangeSong:
		mov     cs:ChangeSongFlag, 1  ; This byte was left over from the "CD-Style" playback function from Dune and KGB.
		                              ; When this byte was enabled, a new song would play after the current song finished
		                              ; playing or ran out of loop count.  This feature doesn't work in MegaRace, as the
		                              ; songs will just stop playing, except for PAGA, DETRITUS, and LENNY, as those songs
		                              ; will play forever.
		mov     al, cs:SongFlag
		retf
		
		;;;
		nop                           ; not in Sound Blaster HERAD driver
		;;;
; ---------------------------------------------------------------------------
; Temporary RAM used for loading song data
TempRAM:
Temp		dw      0                     ;;3BAh
		dw      0                     ;; combined with Temp to become a 32-bit value
Temp2		dw      0                     ;;3BEh
Temp3		db      0                     ;;3C0h
Temp4		db      0                     ;;3C1h
Temp5		dw      0                     ;;3C2h
; ---------------------------------------------------------------------------

GetSongData:
		push    ds
		push    cs
		pop     ds
		mov     ds:ChangeSongFlag, al ; write the low byte of AX to 0x9B
		mov     ax, es:[si]           ; loads SongSize into AX
		mov     di, TempRAM
		mov     [di], si
		mov     word ptr [di+2], es   ; writes SongSegment at 0x2BC
		mov     [di+4], ax            ; writes SongSize at 0x2BE
		mov     ax, es:[si+4000h]     ; grabs word at 0x4000 in SongFile, which is 0x3379 in NewSan (part of a note on...what the hell?)
		mov     [di+6],	ax            ; writes this value at 0x2C0
		mov     ax, es:[si-8000h]     ; okay, this is really weird.  This is suppose to grab ES:[SI-8000], which should be 3BB6:FFFF8000, however, it grabs DS:[SI-8000], which is 3B08:FFFF8000.
		                              ; I think this is happens because of how the segment registers/indexes and pointers work.
		mov     [di+8], ax            ; writes this down at 0x2C2 (for NewSan, it's 0x2790)
		add     si, 2
		mov     ds:SizeOffset, si     ; writes 2 at 0x115
		mov     ds:SongSegment, es    ; writes SongSegment at 0x117
		sub     si, 2
		add     si, es:[si]           ; grab SongSize word at SongSegment
		mov     ds:SongFileSize, si   ; writes SongSize at 0x119
		mov     ds:SongSegment2, es   ; writes SongSegment at 0x11B
		call    ClearSusRel
		call    InitTrackPtrs
		mov     al, ds:EEx19E         ; grab EE at 0x19E and place in low byte at AX
		mov     ds:EEx19C, al         ; write EE at 0x19C
;		call    SoundBlaster
		mov     ds:EEx19D, al         ; grab EE from the low byte of AX and write it at 0x19D
		xor     ax, ax                ; zero out AX
		mov     ds:SongSpeed, ax      ; zero out timer at 0x1D
		mov     ds:SongPlayCount, ax  ; zero out loop count
		call    PlayTick
		mov     al, 80h               ; put 80 in the low byte for AX
		mov     ds:SongFlag, al       ; Turn the SongFlag on by placing 80 there
		pop     ds
		retf

InitTrackPtrs:
		push    ds
		push    ds
		pop     es
		lds     si, dword ptr ds:SizeOffset ; load 0002 from 0x15 in SI
		mov     bp, si                      ; copy 2 from SI to BP
		mov     di, _MidiTrackStart         ; get offset for the start of the MIDI tracks
		mov     cx, TrackNum                ; load 9 into the CX counter

GetTrackOffset:
		lodsw                         ; looks in the music file, skips the first two bytes and loads 32 (first MIDI track offset) into AX, increments SI, repeat 9 times
		or      ax, ax                ; when repeats, get new MIDI track offset
		jz      short InitInstPitch   ; repeat 9 times until zero
		add     ax, bp                ; add 2 to get 34 for absolute address

InitInstPitch:
		stosw                         ; place MIDItrack offset in memory and increment DI so it can get ready to add the next offset
		loop    GetTrackOffset        ; adds all the offsets with loop then jump here to proceed
		mov     di, _MidiInstOffset   ; load Current Instrument offset into DI
		mov     cl, TrackNum          ; place 9 in CX
		mov     ax, 0FFh              ; place FF in AX
		rep stosw                     ; Creates FF for each instrument channel at 0x1EA...it does this by using REP to repeat the STOSW 9 times (9 in CX), STOSW increments the DI, so it creates the bytes in the correct offsets.
		mov     di, _XSlideDurOffset  ; load offset for Pitch Slide Duration Counter in DI
		mov     cl, TrackNum          ; place 9 in CX
		xor     ax, ax                ; when on repeat, get new offset
		rep stosw                     ; zeros out counters
		pop     ds                    ; switch back to driver segment
		les     si, dword ptr ds:SizeOffset ; load 2 into SI

SongInitStart:
		mov     ds:MeasureCount, 1    ; Create 1 measure count for the FourBarCount
		mov     ds:MIDITickCount, MidiTickValue ; Creates the 96 ticks for the MIDITickCount
		mov     cx, TrackNum          ; place 9 in CX
		mov     di, _MidiEventDelay   ; Enter in offset for Current Midi Delay Counter

WriteDelay_Pos:
		mov     si, [di+_MidiTrackStartPos] ; add 24 to 1A2 to get 1C6, then grab the 34 that's at 0x1C6 and store it in SI
		mov     [di+_MidiTrackPos], si ; Creates the 34 at offset 0x1B4 to make the MIDI Track Position
		mov     word ptr [di], 0FFFFh ; places FFFF inside of DS:[01A2]
		or      si, si
		jz      short WriteDelayLoop  ; add 2 to the DI to get the rest of the offsets
		mov     ax, cx                ; places 9 in AX
		call    GetChMidiDelay        ; Creates the first Current Event Midi Tick Counter
		inc     word ptr [di]         ; add 1 to [DI], which will be the MIDI track delay
		mov     cx, ax                ; places 9 in CX.  This will count down as it goes through all 9 tracks

WriteDelayLoop:
		add     di, 2                 ; add 2 to the DI to get the rest of the offsets
		loop    WriteDelay_Pos        ; create the rest of the MIDI track delays
		retn

SongPlay:
		push    ds                    ; check if SongFlag is valid
		mov     ax, cs
		mov     ds, ax
		cmp     ds:SongFlag, 0
		jns     short UpdateBitTimer2   ; if SongFlag byte is not signed
		dec     byte ptr ds:SongSpeed+1 ; decrease second byte of timer
		jns     short UpdateBitTimer    ; jump if not signed
		call    CheckSongSize
		jnz     short UpdateBitTimer2
		push    dx
		push    si
		push    di
		push    bp
		push    es
		call    PlayTick
		pop     es
		pop     bp
		pop     di
		pop     si
		pop     dx

UpdateBitTimer:
		rol     ds:BitTimer, 1        ; rotate bit to the left by 1
		jnb     short UpdateBitTimer2 ; if bit-shift counter reaches 0001, then jump
		call    sub_831

UpdateBitTimer2:
		mov     al, ds:SongFlag
		mov     bx, ds:MeasureCount
		mov     cx, ds:MIDITickCount
		pop     ds
		retf
		
; =============== S U B	R O U T	I N E =======================================


CheckSongSize:	push    si
		push    es
		les     si, dword ptr ds:Temp
		mov     ax, es:[si]           ; move SongSize
		cmp     word ptr ds:Temp2, ax ; SongSize2 is 0x3BE in HERAD Driver. Compare if SongSize is the same with AX
		jnz     short CheckSongSizeEnd
		mov     ax, es:[si+4000h]
		cmp     word ptr ds:Temp3, ax
		jnz     short CheckSongSizeEnd
		mov     ax, es:[si-8000h]
		cmp     word ptr ds:Temp5, ax

CheckSongSizeEnd:
		pop	es
		pop	si
		retn


PlayTick:
		les     bx, dword ptr ds:SizeOffset ; load 0002 into BX
		mov     ax, es:[bx+sSpeed]    ; add 30 to 2 to get 32, which is the offset of the song speed in the music file!  Place that tempo into AX
		add     ds:SongSpeed, ax      ; add the tempo to the value at 0x1D
		mov     di, _MidiEventDelay   ; place the offset for Current Midi Delay Counter into DI
		call    LoopCheck
		mov     cx, TrackNum          ; place 9 in CX

PlayChanLoop:
		dec     word ptr [di]         ; decrease tick count
		jnz     short UpdatePtchSlide

GetMidiEvent:
		mov     si, [di+_MidiTrackPos] ; get offset for MIDI Track Position and place position in SI
		or      si, si
		jz      short DecreaseTick
		push    cx
		push    di
		lods    word ptr es:[si]      ; grab MIDI Event data, place it in AX and increment SI by 2
		mov     dx, di                ; grab offset from DI and place in DX
		sub     dx, _MidiEventDelay   ; subtract 1A2 from DX
		shr     dx, 1                 ; shift right DX by 1
		mov     bx, ax                ; copy delay byte from AX into BX
		and     bx, 70h               ; AND operation on BX with 70
		shr     bx, 1                 ; shift right BX by 1
		shr     bx, 1                 ; shift right BX by 1
		shr     bx, 1                 ; shift right BX by 1
		call    ds:EventPointerTable[bx] ; depending on BX, grab value from MIDI Event Subroutine Lookup Table and jump to offset.
		pop     di
		pop     cx
		cmp     word ptr [di], 0      ; compare 0x1A2 with zero
		jz      short GetMidiEvent    ; if zero, go back up to 3FE, otherwise continue to finish up decreasing the tick.

DecreaseTick:
		add     di, 2                 ; this increases DI by 2 so that the driver will continue on to the next channel
		loop    PlayChanLoop          ; keep looping until CX runs out
		dec     byte ptr ds:MIDITickCount ; decrease MIDI tick!
		jnz     short DecreaseTickEnd ; if not zero, then jump to the end of the subroutine.
		mov     byte ptr ds:MIDITickCount, MidiTickValue ; when ticks reach zero, refresh 4Bar counter to 60 (96 midi ticks)
		inc     ds:MeasureCount	      ; increment the 4 Bar count!

DecreaseTickEnd:
		retn
; ---------------------------------------------------------------------------

UpdatePtchSlide:
		cmp     byte ptr [di+_XSlideDurCount], 0 ; compare low byte at Pitch Slide Duration Counter offset with zero.  Little endian means that our counter is the low byte.
		jz      short DecreaseTick ; if	zero, just decrease the	tick.  if not zero, then continue
		mov     si, [di+_MidiTrackPos]	; grab MIDI delay offset from 0xB4 and copy to SI
		or      si, si
		jz      short DecreaseTick
		push    cx
		push    di
		dec     byte ptr [di+_XSlideDurCount] ; decrease pitch slide counter
		mov     ax, [di+_XSlideCounter] ; grab data at Pitch Slide Counter offset and copy to AX
		add     al, ah                ; add AX's high byte (Pitch Slide Range) to AX's low byte (Pitch Slide Counter)
		mov     [di+_XSlideCounter], al ; write the new pitch slide count!
		mov     dx, di                ; write DI to DX
		sub     dx, _MidiEventDelay   ; subtract 1A2 from DX
		shr     dx, 1                 ; shift bits to the right by 1
		mov     cl, [di+_MidiCurPitch] ; grab the data at 0xEB (MIDI Pitch byte) and write to CX's low byte
		and     cx, 7Fh               ; perform AND with 7F and CX
		jz      short UpdatePtchTick  ; if zero, jump to finish decreasing the tick, otherwise continue.
		mov     ds:Terminator, 0FFh   ; write FF at 0x1C2 (terminator)
		call    BendSetup             ; go to
		mov     ds:Terminator, 0      ; zero out terminator

UpdatePtchTick:
		pop     di
		pop     cx
		jmp     short DecreaseTick


; =============== S U B	R O U T	I N E =======================================


LoopCheck:
		cmp     ds:SongPlayCount, 0   ; compare the loop count with zero
		jnz     short NextLoop
		mov     ax, es:[bx+sLoopStart] ; add 2A to 2 to get 2C, so 3BB6:002C. This is our loop start measure!  Throw that into AX
		cmp     ax, ds:MeasureCount   ; compare the song's loop start measure with the current measure count
		jnz     short LoopCheckEnd    ; jump to short if not equal

GrabLoopPtrs:                                 ; compare the current MIDI tick count with 60
		cmp     ds:MIDITickCount, MidiTickValue 
		jnz     short LoopCheckEnd    ; if it's not 60h, skip this
		push    di
		push    es
		mov     si, di                ; grab DI (1A2) and put it in SI
		add     di, _LoopMidiEventDelay ; add D8 to 1A2 to get 27A (Loop MIDI Delay Values)
		push    ds
		pop     es
		mov     cx, AllTrackPtrs      ; place 12 into CX
		rep movsw                     ; write all the current MIDI delay values into the Loop MIDI Delay Value offsets!
		pop     es
		pop     di
		mov     ax, es:[bx+sLoopCount] ; grab loop count from music file!
		dec     ax                    ; decrease loop count!
		mov     ds:SongPlayCount, ax  ; write loop count to memory!

LoopCheckEnd:
		retn

NextLoop:
		mov     ax, es:[bx+sLoopEnd]  ; grab loop ending measure
		cmp     ax, ds:MeasureCount   ; compare it with the current measure counter
		jnz     short LoopCheckEnd    ; if they don't match, then exit
		dec     ds:SongPlayCount
		push    di
		push    es
		lea     si, [di+_LoopMidiEventDelay]
		push    ds
		pop     es
		mov     cx, AllTrackPtrs
		rep movsw
		pop     es
		pop     di
		mov     ax, es:[bx+sLoopStart]
		mov     ds:MeasureCount, ax


NextLoopEnd:
		retn

; ---------------------------------------------------------------------------
; START	OF FUNCTION CHUNK FOR WriteInstrument

GetDrumMap:
		mov     [di+_MidiDrumMapPtr], si ; write drummap instrument offset to 0xD8!
		retn
; END OF FUNCTION CHUNK	FOR WriteInstrument

; =============== S U B	R O U T	I N E =======================================


InstChange_C0:
		mov     word ptr [di+_MidiDrumMapPtr], 0 ; zeros out drum instrument offsets when instrument change occurs
		call    GetChMidiDelay


; =============== S U B	R O U T	I N E =======================================


WriteInstrument:
		cmp     [di+_MidiCurInst], ah ; compare the high byte of AX with 1EA
		jz      short NextLoopEnd     ; jump if zero
		mov     [di+_MidiCurInst], ah ; write instrument number to memory!
		mov     al, InstSize          ; load 28 into low byte of AX
		mul     ah                    ; multiply high byte of AX, which is zero, so the answer is zero
		les     si, dword ptr ds:SongFileSize ;	load SongSize in SI
		add     si, ax                ; add AX to SI
		mov     al, es:[si]           ; grab low byte at SongSegment:SongSize
		cmp     al, iDrumMode         ; compare low byte if it's an FF (Drummap)
		jz      short GetDrumMap      ; If it is, get drum map!
		mov     ax, es:[si+iX_SlideTrans] ; grab instrument's Pitch Slide Range Flag / Transpose bytes
		mov     [di+_XSlideRangeFlag], ax ; write them to memory!
;		mov     ah, es:[si+iC_Level]  ; grab the Carrier Output Level and place it as high byte in AX
;		mov     al, es:[si+iM_Level]  ; grab the Modulator Output Level and copy it as the low byte for AX

		mov	al, ds:EEx19C
		mov	ah, al
		add	ah, es:[si+iC_Level]
		add	al, es:[si+iM_Level]
		cmp	al, 3Fh
		jb	short loc_5D4
		mov	al, 3Fh

loc_5D4:
		cmp	ah, 3Fh
		jb	short loc_5DB
		mov	ah, 3Fh

loc_5DB:
		mov     bh, es:[si+iM_KSL]    ; grab the Modulator Key scaling level, copy into high byte for BX
		mov     bl, es:[si+iC_KSL]    ; grab the Carrier Key scaling level, copy into low byte for BX
		and     bx, 303h
		ror     bx, 1
		ror     bx, 1
		or      ax, bx
		mov     [di+_FMOutputLevel], ax	; write	Modulator Output Level (first byte) / Carrier Output Level (Second byte) into memory!
		mov     ax, es:[si+iX_MLevelScale] ; grab the Modulator and Carrier Output Level Scaling
		mov     [di+_FMOutputScaling], ax ; write scaling bytes to memory at 0x132!
		mov     ah, es:[si+iFeedback] ; grab feedback and place it in high byte for AX
		mov     bl, es:[si+iPanning]  ; grab panning byte, put it in low byte for BX
		shl     bl, 1
		shl     bl, 1
		shl     bl, 1
		or      ah, bl                ; grab new panning byte and put it in high byte in AX
		mov     al, es:[si+iConnector] ; grab Connector and place it in low byte for AX
		not     al
		ror     al, 1
		shl     ax, 1
		mov     al, es:[si+iX_FBScaleVEL] ; grab Feedback Scaling - Velocity byte, place it in low byte for AX
		mov     [di+_FMFeedbackRegister], ax ; write Panning/Feedback/Connector Register (first byte) / Feedback Scaling (second byte) at 0x168
		mov     ax, es:[si+iX_SlideDurRange] ; grab Pitch Slide Duration / Pitch Slide Range, throw into AX
		mov     [di+_XSlideRange], ah ; grab Pitch Slide Range and place it at 0x121
		mov     ah, al                ; change Pitch Slide Duration byte
		xor     al, al                ; zero out low byte
		mov     [di+_XSlideDurCount], ax ; write Pitch Slide Duration at 0x10E
		push    ds
		mov     ax, es                ; place SongSegment in AX
		mov     ds, ax                ; place SongSegment in DS
		add     si, 2                 ; add 2 to SongSize
		call    LoadInstrument
		pop     ds
		retn

; =============== S U B	R O U T	I N E =======================================


NoteOn_90:
		lods    byte ptr es:[si]      ; get MIDI Pitch
		call    GetChMidiDelay        ; write the MIDI delay and track position counts
		mov     si, [di+_MidiDrumMapPtr] ; get drummap instrument offset at 0xD8
		or      si, si
		jz      short Transpose       ; if there's no drummap, jump to 58B
		push    ax
		push    dx
		push    si
		push    di
		push    es
		mov     es, cs:SongSegment2   ; grab SongSegment and put it in ES
		mov     al, ah                ; grab MIDI pitch and put it in AX's low byte
		sub     al, es:[si+2]         ; grab the 0x18 transpose byte from the drum keymap instrument and subtract it from the MIDI pitch at AX's low byte
		xor     ah, ah                ; zero out the MIDI pitch at AX's high byte
		;sub    ax, 14h               ; subtract 0x14 from AX's value
		;;;;;;;;;;;;;;;;;;;;;;
		db      2Dh
		dw      14h
		;;;;;;;;;;;;;;;;;;;;;
		add     si, ax                ; add the value from AX into SI, which is the drum keymap instrument offset.  This will take us to the instrument number inside the keymap array.
		mov     ah, es:[si]           ; grab the instrument byte in the keymap array and place it in AX's high byte
		call    WriteInstrument
		pop     es
		pop     di
		pop     si
		pop     dx
		pop     ax

Transpose:
		mov     bh, [di+_XRootNoteTrans] ; grab transpose byte and place in the high byte of BX
		mov     bl, bh                ; copy transpose value to low byte of BX
		sub     bh, 31h               ; subtract 31 from the transpose value
		cmp     bh, 60h               ; compare the transpose value at BX's high byte to 60.  The result will change the CF flag.
		jnb     short WriteTranspose  ; if transpose value is less than 60 (CF flag is 1), DON'T jump
		mov     ah, bh                ; copy the subtracted transpose byte to replace the MIDI byte at AX's high byte
		xor     bl, bl                ; zero out the original transpose value
		add     ah, 18h               ; add 18 to the subtracted transpose byte

WriteTranspose:
		add     ah, bl                ; add BX's low byte to AX's high byte.  This should change the MIDI pitch to the new transposed pitch.
		push    ax                    ; place AX's value in the stack
		call    sub_632
		cmp     byte ptr [di+_MidiCurPitch], 0 ; compare MIDI pitch with zero
		jle     short WriteMidiPitch  ; jump if less or equal
		test    byte ptr [di+0FDh], 2
		jnz     short WriteMidiPitch
		xor     ax, ax
		call    NoteWrite

WriteMidiPitch:
		pop     ax                    ; place MIDI pitch and velocity back in AX
		mov     al, ah                ; copy pitch byte to AX's low byte
		xor     ah, ah                ; zero out AX's high byte
		mov     [di+_MidiCurPitch], al ; write the MIDI pitch!
		;sub    ax, 48h               ; AX - 48 = value
		;;;;;;;;;;;;;;;;;;;;;;;;
		db      2Dh
		dw      48h
		;;;;;;;;;;;;;;;;;;;;;;;;
		mov     cl, [di+_XSlideDuration] ; take the Pitch Slide Duration byte and place it in CX's low byte
		mov     [di+_XSlideDurCount], cl ; take the Pitch Slide Duration value in CX and place it at the Pitch Slide Duration Counter offset
		mov     byte ptr [di+_XSlideCounter], SlideCenter ; resets the pitch slide by writing 40 at 0x10E
		jmp     loc_95C               ; jump to 95C


; =============== S U B	R O U T	I N E =======================================


NoteOff_80:
		call    GetChMidiDelay

loc_5D2:
		mov     bh, [di+_XRootNoteTrans] ; grab transpose byte and place it in BX's high byte
		mov     bl, bh                ; copy BX's high byte to BX's low byte
		sub     bh, 31h               ; subtract 31 from BX's high byte
		cmp     bh, 60h               ; compare the transpose value at BX's high byte to 60.  The result will change the CF flag.
		jnb     short loc_5E6         ; if transpose value is less than 60 (CF flag is 1), DON'T jump
		mov     ah, bh                ; copy the subtracted transpose byte to replace the MIDI byte at AX's high byte
		xor     bl, bl                ; zero out the original transpose value
		add     ah, 18h               ; add 18 to the subtracted transpose byte

loc_5E6:
		add     ah, bl                ; add zero?  this doesn't do anything
		cmp     [di+_MidiCurPitch], ah ; compare the MIDI pitch byte with AX's high byte
		jnz     short NoteOffEnd      ; if the bytes are not the same, jump
		or      byte ptr [di+_MidiCurPitch], 80h ; write the NoteOff to memory!
		jmp     KeyOffChan

NoteOffEnd:
		retn


; =============== S U B	R O U T	I N E =======================================


EndofTrack_FF:
		mov     word ptr [di], 0FFFFh ; write FFFF at the Current Midi Delay Counter offset
		sub     word ptr [di+_MidiTrackPos], 2 ; subtract 2 from the MIDI Track Position offset
		or      dx, dx                ; [dx was zero here]
		jnz     short locret_61C
		dec     ds:ChangeSongFlag     ; SongChange is decreased to zero
		jz      short ClearStop       ; jump if zero
		jns     short loc_60D
		inc     ds:ChangeSongFlag

loc_60D:
		call    SongInitStart
		les     bx, dword ptr ds:SizeOffset
		mov     di, _MidiEventDelay
		call    LoopCheck
		dec     word ptr [di]

locret_61C:
		retn
; ---------------------------------------------------------------------------

ClearStop:
		mov     ax, 0FFFFh            ; put FFFF in AX
		push    es
		push    ds
		pop     es
		mov     cx, TrackNum
		rep stosw                     ; write FFFF in ALL the MIDI Track Position offsets!
		pop     es
		push    cs
		call    near ptr ShutUp
		retn


; =============== S U B	R O U T	I N E =======================================


Aftertouch_D0:
		call    GetChMidiDelay
		retn


; =============== S U B	R O U T	I N E =======================================


sub_632:
		mov     ah, al                ; copy the velocity byte to AX's high byte
		mov     al, 80h               ; place 80 in AX's low byte
		sub     al, ah                ; subtract 80 from the velocity byte
		mov     bx, [di+_FMOutputLevel] ; grab the output level bytes at 0x144 and place them in BX
		mov     cx, [di+_FMOutputScaling] ; grab the output level scaling bytes at 0x132 and place them in CX.
		or      cl, cl
		jz      short loc_673         ; jump if zero
		push    ax
		jns     short loc_64B
		neg     cl
		mov     al, ah                ; change Pitch Slide Range

loc_64B:
		sub     cl, 4
		neg     cl
		shr     al, cl
		mov     ah, bl
		and     ah, 3Fh
		add     ah, al
		cmp     ah, 3Fh

loc_65C:
		jbe     short loc_660
		mov     ah, 3Fh

loc_660:
		and     bl, 0C0h
		or      bl, ah
		mov     ah, bl
		mov     si, OPLPortTable
		add     si, dx
		lodsb
		add     al, 40h
		call    ChipWrite
		pop     ax

loc_673:
		or      ch, ch
		jz      short loc_6A5         ; jump if zero
		push    ax
		jns     short loc_67E
		neg     ch
		mov     al, ah

loc_67E:
		mov     cl, 4
		sub     cl, ch
		shr     al, cl
		mov     ah, bh
		and     ah, 3Fh
		add     ah, al
		cmp     ah, 3Fh
		jbe     short loc_692
		mov     ah, 3Fh

loc_692:
		and     bh, 0C0h
		or      bh, ah
		mov     ah, bh
		mov     si, FineBendTable
		add     si, dx
		lodsb
		add     al, 40h
		call    ChipWrite
		pop     ax

loc_6A5:
		mov     [di+_FMOutputRegister], bx ; grab BX and place it at Output Level Register value (0x156)
		mov     cx, [di+_FMFeedbackRegister] ; grab the Panning/Feedback/Connector Register Value (0x168) and place in CX
		or      cl, cl
		jnz     short loc_6B2         ; jump if not zero (ZF = 0)
		retn
; ---------------------------------------------------------------------------

loc_6B2:
		jns     short loc_6B8
		neg     cl
		mov     al, ah

loc_6B8:
		sub     cl, 6
		neg     cl
		shr     al, cl
		mov     ah, ch
		and     ax, 0FFEh
		add     al, ah
		cmp     al, 0Fh
		jbe     short loc_6CE
		and     al, 0Fh
		or      al, 0Eh

loc_6CE:
		mov     ah, al
		and     ch, 30h
		or      ah, ch
		mov     al, dl
		add     al, 0C0h
		call    ChipWrite


locret_6DC:
		retn

; =============== S U B	R O U T	I N E =======================================


PitchBend_E0:
		mov     al, ah                ; copy pitch bend byte from AX's high byte to low byte
		call    GetChMidiDelay


; =============== S U B	R O U T	I N E =======================================


BendSetup:
		mov     cl, [di+_MidiCurPitch] ; grab the data at 0xEB (MIDI Pitch byte) and write to CX's low byte
		or      cl, cl
		jle     short locret_6DC      ; jump if less or equal to
		xor     ch, ch                ; clear CX's high byte
		mov     ah, ch                ; copy zero to AX's high byte, this overwrites the Pitch Slide Range byte
		xchg    ax, cx                ; switch cx with ax (CX is now pitch slide count, AX is now MIDI pitch)
		sub     al, 18h               ; subtract 18 from MIDI pitch
		mov     bl, 0Ch               ; write C to BX's low byte
		div     bl                    ; divide AX by BX's low byte
		xchg    ax, cx                ; switch cx with ax (CX is now MIDI pitch, AX is now pitch slide count)

loc_6F5:
		mov     bx, [di+10Eh]         ; copy data at 0x1B0 (3B08:02B0) and place in BX (the data at this offset should be just zeros)
		or      bh, cs:Terminator     ; grab terminator byte at 0x1C2 and perform OR with BX's high byte (BX now becomes FF00)
		cmp     byte ptr [di+_XSlideRangeFlag], 0 ; compare Pitch Slide Range Flag to zero
		jnz     short BendFlagOn      ; if Pitch Slide Range Flag is zero, continue; otherwise, jump
		;sub    ax, 40h               ; subtract 40 from pitch slide count
		;;;;;;;;;;;;;;;;;;;;;;;;
		db      2Dh
		dw      40h
		;;;;;;;;;;;;;;;;;;;;;;;;
		jnb     short BendUp          ; Jump short if not below (jump if the pitch bend goes up)
		neg     ax                    ; get the two's compliment from AX
		ror     ax, 1                 ; rotate bits to the right
		ror     ax, 1
		ror     ax, 1
		ror     ax, 1
		ror     ax, 1
		sub     ch, al                ; subtract CX's high byte (modified MIDI pitch) with AX's low byte (modified pitch bend)
		jnb     short loc_722
		add     ch, 0Ch               ; add C to CX's high byte
		dec     cl                    ; decrease CX's low byte
		jns     short loc_722
		xor     cx, cx

loc_722:
		mov     al, ch                ; copy CX's high byte to AX's low byte
		mov     bx, unk_BendTable     ; place 183 into BX
		xlat                          ; grab byte from table 0x83 (DS:BX), using AX's low byte as a table index!
		mul     ah                    ; multiply AX's low byte and high byte together
		mov     al, ah                ; copy AX's high byte to the low byte
		xchg    al, ch                ; switch CX's high byte with AX's low byte

GetFreq:
		xor     ah, ah                ; zero out AX's high byte
		add     ax, ax                ; AX + AX (this value is now our table index for our note's frequency!)
		mov     si, ax                ; place AX into SI
		mov     ax, [si+FreqTable]    ; look up freq table and grab correct note frequency!
		sub     al, ch                ; subtract the low byte of the frequency with the value in CX's high byte
		sbb     ah, 0                 ; Adds 0 and the carry (CF) flag, and subtracts the result from AX's high byte. The result of the subtraction is stored in AX's high byte.
		jmp     NoteKeyOn
; ---------------------------------------------------------------------------

BendUp:
		inc     ax                    ; increase AX by 1
		ror     ax, 1                 ; rotate bits to the right, 5 times
		ror     ax, 1
		ror     ax, 1
		ror     ax, 1
		ror     ax, 1
		add     ch, al                ; add the low byte of AX to the high byte of CX
		cmp     ch, 0Ch               ; compare C to the high byte of CX
		jb      short loc_757         ; jump if below C
		sub     ch, 0Ch
		inc     cl

loc_757:
		mov     al, ch                ; copy CX's high byte to AX's low byte
		mov     bx, unk_BendTable+1   ; place 184 in BX
		xlat                          ; using AX's low byte as a table index, grab a byte starting from the table at 0x84 and place that byte as the low byte for AX.
		mul     ah                    ; multiply the high byte and low byte of AX
		mov     al, ah                ; copy AX's high byte to AX's low byte
		jmp     short GetFrequency    ; switch CX's high byte with AX's low byte
; ---------------------------------------------------------------------------

BendFlagOn:
		;sub    ax, 40h               ; take the pitch slide counter value and subtract it by 40
		;;;;;;;;;;;;;;;;;;;;;;;;
		db      2Dh
		dw      40h
		;;;;;;;;;;;;;;;;;;;;;;;;
		jnb     short CoarseBendUp    ; if signed, continue
		neg     ax                    ; two's compliment
		mov     bh, 5
		div     bh                    ; divide that value by 5
		sub     ch, al
		jnb     short GrabCoarseTable
		add     ch, 0Ch
		dec     cl
		jns     short GrabCoarseTable
		xor     cx, cx

GrabCoarseTable:
		mov     al, ah
		mov     bx, CoarseBendTable
		cmp     ch, 6
		jb      short GrabFreqTable
		add     bx, 5

GrabFreqTable:
		xlat                          ; Using the table at 0x90 (3B08:0190), use AX's low byte to index the table and place the value in AX
		xchg    al, ch
		xor     ah, ah
		add     ax, ax
		mov     si, ax
		mov     ax, [si+FreqTable]
		sub     al, ch
		sbb     ah, 0
		jmp     short NoteKeyOn
; ---------------------------------------------------------------------------

CoarseBendUp:
		mov     bh, 5
		div     bh
		add     ch, al
		cmp     ch, 0Ch
		jb      short loc_7AC
		sub     ch, 0Ch
		inc     cl

loc_7AC:
		mov     al, ah
		mov     bx, 190h
		cmp     ch, 6
		jb      short loc_7B9
		add     bx, 5

loc_7B9:
		xlat

GetFrequency:
		xchg    al, ch                ; switch CX's high byte with AX's low byte
		xor     ah, ah                ; zero out AX's high byte
		add     ax, ax                ; add AX with AX
		mov     si, ax                ; copy AX to SI
		mov     ax, [si+FreqTable]    ; grab the value at 0x47 (Frequency Table) and copy to AX
		add     al, ch                ; add CX's high byte to AX's low byte
		adc     ah, 0                 ; add with carry flag to AX's high byte

NoteKeyOn:
		shl     cl, 1                 ; shift CX's low byte bits to the left, two times
		shl     cl, 1
		or      ah, cl                ; perform OR on CX's low byte and AX's high byte and write it to AX's high byte
		mov     si, dx                ; copy DX to SI
		add     si, si                ; add SI with itself
		mov     [si+FNumRegisters], ax	; write	new FNUM register value!
		cmp     byte ptr [di+_MidiCurPitch], 0 ; compare zero with 0xEB (MIDI pitch)

loc_7DD:
		jz      short loc_7E2         ; jump if zero, otherwise continue
		or      ah, 20h               ; perform OR with 20 and AX's high byte

loc_7E2:
		jmp     NoteWrite


; =============== S U B	R O U T	I N E =======================================


GetChMidiDelay:
		push    ax
		xor     ax, ax                ; zero out AX
		lods    byte ptr es:[si]      ; grab MIDI delay byte at ES (SongSegment):[SI] (TrackPosition).   Increment SI by 1
		or      al, al
		jns     short UpdateTrackPos  ; Jump if the delay byte not signed.  If the byte is 80 or above, we got more work to do.
		xor     cx, cx                ; zero out CX

GrabMidiDelay:
		mov     ch, cl                ; take the low byte of CX and copy it to the high byte of CX
		mov     cl, ah                ; take the high byte of AX and copy it to the low byte of CX
		mov     ah, al                ; take the low byte of AX and copy it to the high byte of AX
		lods    byte ptr es:[si]      ; grab MIDI delay byte at ES (SongSegment):[SI] (TrackPosition) again.   Increment SI by 1 again.  If the previous delay byte is larger than 7F, this is where the second delay byte will go.
		or      al, al
		js      short GrabMidiDelay   ; take the low byte of CX and copy it to the high byte of CX
		and     ax, 7F7Fh             ; perform AND on AX with 7F7F.  Each bit of the result of the AND instruction is a 1 if both corresponding bits of the operands are 1; otherwise, it becomes a 0.
		and     cx, 7F7Fh             ; perform AND on CX with 7F7F
		shl     cl, 1                 ; shift logical left 1 bit at low byte of CX, ZF flag changes
		shr     cx, 1                 ; shift logical right 1 bit for CX
		shl     al, 1                 ; shift logical left 1 bit at low byte of AX, ZF flag changes
		shl     ax, 1                 ; shift logical left 1 bit at AX (basically slide everything to the left, add a zero at the end and disregard MS Bit)
		shr     cx, 1                 ; shift logical right 1 bit for CX
		rcr     ax, 1                 ; RCR instruction shifts the CF flag into the most-significant bit and shifts the least-significant bit into the CF flag
		shr     cx, 1                 ; getting repetitive, ain't it?
		rcr     ax, 1                 ; THIS is your delay!!
		jcxz    short UpdateTrackPos  ; Jump short if CX register is 0
		mov     ax, 0FFFFh            ; if no track exists, put FFFF in AX

UpdateTrackPos:
		mov     [di], ax              ; take your delay word and place it in memory!
		mov     [di+_MidiTrackPos], si ; update Current Track Position
		pop     ax                    ; pop AX to get original value again
		retn


; =============== S U B	R O U T	I N E =======================================


KeyOffAll:
		push    ds
		push    cs
		pop     ds
		mov     cx, TrackNum          ; place 9 in CX

KeyOffLoop:
		push    cx
		mov     dx, cx                ; copy CX into DX
		dec     dx                    ; decrease DX
		call    KeyOffChan
		pop     cx
		loop    KeyOffLoop            ; repeat until CX is depleted
		pop     ds
		retn


; =============== S U B	R O U T	I N E =======================================


sub_831:
		mov     al, ds:EEx19C         ; copy EE byte at 0x9C into the low byte of AX
		cmp     al, ds:EEx19D         ; compare this byte with the byte at 0x9D
		jnz     short loc_846         ; if not zero, jump to 846
		mov     ds:BitTimer, 1        ; copy 1 to 0x9F
		and     ds:SongFlag, 0BFh     ; check if SongFlag is above CO
		retn
; ---------------------------------------------------------------------------

loc_846:
;		mov     ah, al
;		mov     bl, ds:EEx19D
;		mov     bh, bl
;		and     al, 0Fh
;		and     bl, 0Fh
;		cmp     al, bl
;		jz      short loc_85F
;		inc     ah
;		jb      short loc_85F
;		dec     ah
;		dec     ah
;
;loc_85F:
;		mov     al, ah
;		and     ah, 0F0h
;		and     bh, 0F0h
;		cmp     ah, bh
;		jz      short loc_873
;		add     al, 10h
;		cmp     ah, bh
;		jb      short loc_873
;		sub     al, 20h
;
;loc_873:
;		mov     ds:EEx19C, al
;		or      al, al
;		jnz     short loc_88A
;		push    dx
;		push    si
;		call    KeyOffAll
;		pop     si
;		pop     dx
;		mov     ds:SongFlag, 0
;
;
;; =============== S U B	R O U T	I N E =======================================
;
;
;SoundBlaster:
;		mov     al, cs:EEx19C         ; grab EE at 0x9C and place in low byte at AX
;
;loc_88A:
;		mov     ah, 26h               ; place 26 at high byte in AX.  Now we have 26EE
;		push    dx
;		mov     dx, word ptr cs:PortNum ; grab 0220 at 0x1C6, put it in	DX
;		add     dl, 4                 ; make it 224
;		xchg    al, ah                ; exchange the low byte with the high byte at AX. Now we have EE26
;		out     dx, al                ; send the low byte of AX (26) to I/O port 224
;		inc     dx                    ; increment DX, now it's 225
;		xchg    al, ah                ; exchange the low byte with the high byte at AX. Now we have 26EE again.
;		out     dx, al                ; send the low byte of AX (EE) to I/O port 225

		;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Start of DFADL only code
		
		push    dx
		push    si
		push    di
		push    bp
		push    es
		jnb     short loc_929
		jmp     loc_9B1
; ---------------------------------------------------------------------------

loc_929:
		mov     di, _MidiEventDelay
		mov     si, OPLPortTable
		mov     cx, TrackNum

loc_932:
		mov     ah, [di+_MidiCurInst]
		cmp     ah, 0FFh
		jz      short loc_999
		mov     al, InstSize
		mul     ah
		les     bp, ds:119h
		add     bp, ax
		mov     al, [di+_FMOutputLevel]
		mov     ah, [di+_FMOutputRegister]
		mov     bx, ax
		and     al, 3Fh
		cmp     al, es:[bp+iM_Level]
		jbe     short loc_96E
		dec     bl
		mov     [di+_FMOutputLevel], bl
		and     bh, 3Fh
		jz      short loc_96E
		dec     ah
		mov     [di+_FMOutputRegister], ah
		mov     al, [si]
		add     al, 40h
		call    ChipWrite

loc_96E:
		mov     al, [di+_FMOutputLevel+1]
		mov     ah, [di+_FMOutputRegister+1]
		mov     bx, ax
		and     al, 3Fh
		cmp     al, es:[bp+17h]
		jb      short loc_999
		dec     bl
		mov     [di+_FMOutputLevel+1], bl
		and     bh, 3Fh
		jz      short loc_999
		dec     ah
		mov     [di+_FMOutputRegister+1], ah
		mov     al, [si+TrackNum]
		add     al, 40h
		call    ChipWrite

loc_999:
		add     di, 2
		inc     si
		loop    loc_932
		dec     cs:EEx19C
		jns     short loc_9AB
		inc     cs:EEx19C

loc_9AB:
		pop     es
		pop     bp
		pop     di
		pop     si
		pop     dx
		retn
; ---------------------------------------------------------------------------

loc_9B1:
		mov     di, _FMOutputOffset
		mov     si, OPLPortTable
		mov     cx, TrackNum

loc_9BA:
		mov     al, [di]
		mov     ah, [di+_MidiTrackPos]
		mov     bx, ax
		and     al, 3Fh
		cmp     al, 3Fh
		jz      short loc_9CB
		inc     bl
		mov     [di], bl

loc_9CB:
		and     bh, 3Fh
		cmp     bh, 3Fh
		jz      short loc_9DF
		inc     ah
		mov     [di+_MidiTrackPos], ah
		mov     al, [si]
		add     al, 40h
		call    ChipWrite

loc_9DF:
		inc     di
		mov     al, [di]
		mov     ah, [di+_MidiTrackPos]
		mov     bx, ax
		and     al, 3Fh
		cmp     al, 3Fh
		jz      short loc_9F1
		inc     bl
		mov     [di], bl

loc_9F1:
		and     bh, 3Fh
		cmp     bh, 3Fh
		jz      short loc_A06
		inc     ah
		mov     [di+_MidiTrackPos], ah
		mov     al, [si+TrackNum]
		add     al, 40h
		call    ChipWrite

loc_A06:
		inc     di
		inc     si
		loop    loc_9BA
		inc     cs:EEx19C
		cmp     cs:EEx19C, 3Fh
		jnz     short loc_A20
		call    KeyOffAll
		mov     cs:SongFlag, 0

loc_A20:
		pop     es
		pop     bp
		pop     di
		pop     si
		;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; End of DFADL only code
		pop     dx
		retn



; =============== S U B	R O U T	I N E =======================================


ClearSusRel:
		mov     si, OPLPortTable      ; places 171 in SI
		mov     cx, AllTrackPtrs      ; places 12 in CX
		mov     ah, 0FFh              ; places 0xFF at high byte in AX

ClearSusLoop:
		lodsb                         ; grabs the byte at 0x71, which is 00, and places it in the low byte of AX, which gives us FF00.  SI increments to 172.
		add     al, 80h               ; add 80, which gives us FF80.  The lookup table at 0x71 is for cycling through all the OPL registers and adding each byte, one at a time to 80, thus giving us OPL registers 80-95.
		call    ChipWrite             ; writes FF at OPL register 80
		loop    ClearSusLoop          ; do this 18 times, for OPL registers 80-95.
		retn


; =============== S U B	R O U T	I N E =======================================


LoadInstrument:
		add     dx, dx
		mov     bx, dx
		mov     dx, cs:[bx+OPLRegTable] ; Table at 0x35
		shr     bx, 1
		call    LoadChanSlot
		xchg    dh, dl
		mov     ah, [si+1Bh]          ; after loading the instrument, get ready to grab stuff from the next instrument
		add     si, 0Dh               ; after the first pass of grabbing the mod stuff, now get the carrier stuff
		jmp     short LoadSlotOnly


; =============== S U B	R O U T	I N E =======================================


LoadChanSlot:
		mov     ah, [si+0Ch]          ; grab connector byte
		shr     ax, 1
		mov     ah, [si+2]            ; grab feedback
		not     al
		shl     ax, 1
		and     ah, 0Fh
		mov     al, 0C0h
		add     al, bl
		call    ChipWrite
		mov     ah, [si+1Ah]          ; grab modulator waveform

LoadSlotOnly:
		and     ah, 3
		mov     al, 0E0h
;loc_8E5:
		add     al, dl
		call    ChipWrite
		;;;;;;;;;;;;;;;;;     ;; New instructions for DFADL
		mov	ah, cs:EEx19C
		add     ah, [si+8]            ; Modulator Output Level?
		cmp	ah, 3Fh
		jb	short loc_A81
		mov	ah, 3Fh
		;;;;;;;;;;;;;;;;;

loc_A81:
		mov     al, [si]              ; Modulator Key scaling level
		shl     ah, 1
		shl     ah, 1
		ror     ax, 1
		ror     ax, 1
		mov     al, 40h
		add     al, dl
		call    ChipWrite
		mov     ah, [si+3]            ; Modulator Attack
		mov     al, [si+6]            ; Modulator Delay
		shl     al, 1
		shl     al, 1
		shl     al, 1
		shl     al, 1
		shl     ax, 1
		shl     ax, 1
		shl     ax, 1
		shl     ax, 1
		mov     al, 60h
		add     al, dl
		call    ChipWrite
		mov     ah, [si+4]            ; Modulator Sustain
		mov     al, [si+7]            ; Modulator Release
		shl     al, 1
		shl     al, 1
		shl     al, 1
		shl     al, 1
		shl     ax, 1
		shl     ax, 1
		shl     ax, 1
		shl     ax, 1
		mov     al, 80h
		add     al, dl
		call    ChipWrite
		mov     al, [si+0Bh]          ; Modulator Key scaling/envelope rate
		ror     ax, 1
		mov     al, [si+5]            ; Modulator Envelope gain
		ror     ax, 1
		mov     al, [si+0Ah]          ; Modulator Frequency Vibrato
		ror     ax, 1
		mov     al, [si+9]            ; Modulator Amplitude modulation (Tremolo)
		ror     ax, 1
		mov     al, [si+1]            ; Modulator Frequency multiplier
		and     ax, 0F00Fh
		or      ah, al
		mov     al, 20h
		add     al, dl
		call    ChipWrite
		retn

loc_95C:
		;add    ax, 30h               ; take subtracted pitch value and add 30
		;cmp    ax, 60h               ; compare 60 to AX (AX - 60)
		;;;;;;;;;;;;;;;;;;;;;;;;;;
		db      05
		dw      30h                   ; add ax, 30h
		
		db      3Dh
		dw      60h                   ; cmp ax, 60h
		;;;;;;;;;;;;;;;;;;;;;;;;;;
		jb      short KeyOnChan       ; If AX < 60 then jump (CF=1)
		xor     ax, ax                ; zero out AX

KeyOnChan:
		mov     bl, 0Ch               ; place C in low byte of BX
		div     bl                    ; divide AX by BX's low byte
		mov     cl, al                ; copy low byte of AX into low byte of CX
		xchg    ah, al                ; exchange low byte of AX with high byte of AX
		xor     ah, ah                ; zero out high byte of AX
		add     ax, ax                ; AX + AX
		mov     si, ax                ; copy AX into SI
		mov     ax, [si+FreqTable]    ; grab frequency number from table and copy into AX
		shl     cl, 1                 ; shift bit to the left by 1 in low byte of CX
		shl     cl, 1                 ; shift bit to the left by 1 in low byte of CX
		or      ah, cl                ; OR low byte of CX with high byte of AX
		mov     si, dx                ; copy DX into SI
		add     si, si                ; SI + SI
		mov     [si+FNumRegisters], ax ; write the FNUM register value!!
		or      ah, 20h               ; write KEY-ON register bit
		jmp     short NoteWrite

; =============== S U B	R O U T	I N E =======================================


KeyOffChan:
		mov     si, dx                ; copy DX into SI
		add     si, si                ; add SI + SI
		mov     ax, [si+FNumRegisters] ; grab FNUM register and copy to AX

NoteWrite:
		mov     cx, ax                ; copy the register value into CX
		mov     al, dl                ; then copy the	low byte of DX,	replacing the low byte of AX
		add     al, 0A0h              ; add A0 to the low byte of AX (this is the write register for  FNUM (Lower 8 bits))
		mov     ah, cl                ; copy the low byte of CX to the high byte of AX
		mov     si, ax                ; copy AX to SI
		call    ChipWrite
		mov     ax, si                ; copy SI to AX
		add     al, 10h               ; add 10 to the	low byte of AX (A0 becomes BO, which is	the write register for KEY-ON, Block Number, FNUM (high	bits))


		mov     ah, ch                ; copy the high	byte of	CX to the high byte of AX

; =============== S U B	R O U T	I N E =======================================



ChipWrite:
		push    dx
		mov     dx, 388h
		out     dx, al
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		inc     dx
		mov     al, ah
		out     dx, al
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		in      al, dx
		pop     dx
		retn