OS SERIES 8
GEOFF COX

*************************************************************************
*                                                                       *
*        OSBYTE &F7 (247) INTERCEPT BREAK                               *
*                                                                       *
*************************************************************************

EAD9	LDA &0287   ;get BREAK vector code
EADC	EOR #&4C    ;produces 0 if JMP not in &287
EADE	BNE &EAF3   ;if not goto EAF3
EAE0	JMP &0287   ;else jump to user BREAK code


*************************************************************************
*                                                                       *
*        OSBYTE &90 (144)   *TV                                         *
*                                                                       *
*************************************************************************

    	    ;X=display delay
    	    ;Y=interlace flag

EAE3	LDA &0290   ;VDU vertical adjustment
EAE6	STX &0290   ;store new value
EAE9	TAX         ;put old value in X
EAEA	TYA         ;put interlace flag in A
EAEB	AND #&01    ;maximum value =1
EAED	LDY &0291   ;get old value into Y
EAF0	STA &0291   ;put new value into A
EAF3	RTS         ;and Exit


*************************************************************************
*                                                                       *
*        OSBYTE &93 (147)  WRITE TO FRED                                *
*                                                                       *
*************************************************************************

    	            ;X is offset within page
    	            ;Y is byte to write
EAF4	TYA         ;
EAF5	STA &FC00,X ;
EAF8	RTS         ;


*************************************************************************
*                                                                       *
*        OSBYTE &95 (149)  WRITE TO JIM                                 *
*                                                                       *
*************************************************************************

    	            ;X is offset within page
    	            ;Y is byte to write
    	            ;
EAF9	TYA         ;
EAFA	STA &FD00,X ;
EAFD	RTS         ;


*************************************************************************
*                                                                       *
*        OSBYTE &97 (151)  WRITE TO SHEILA                              *
*                                                                       *
*************************************************************************

    	            ;X is offset within page
    	            ;Y is byte to write

EAFE	TYA         ;
EAFF	STA &FE00,X ;
EB02	RTS         ;


****************** Silence a sound channel *******************************
    	            ;X=channel number

EB03	LDA #&04    ;mark end of release phase
EB05	STA &0808,X ;to channel X
EB08	LDA #&C0    ;load code for zero volume

****** if sound not disabled set sound generator volume ******************

EB0A	STA &0804,X ;store A to give basic sound level of Zero
EB0D	LDY &0262   ;get sound output/enable flag
EB10	BEQ &EB14   ;if sound enabled goto EB14
EB12	LDA #&C0    ;else load zero sound code
EB14	SEC         ;set carry
EB15	SBC #&40    ;subtract &40
EB17	LSR         ;divide by 8
EB18	LSR         ;to get into bits 0 - 3
EB19	LSR         ;
EB1A	EOR #&0F    ;invert bits 0-3
EB1C	ORA &EB3C,X ;get channel number into top nybble
EB1F	ORA #&10    ;

EB21	PHP         ;

EB22	SEI         ;disable interrupts
EB23	LDY #&FF    ;System VIA port A all outputs
EB25	STY &FE43   ;set
EB28	STA &FE4F   ;output A on port A
EB2B	INY         ;Y=0
EB2C	STY &FE40   ;enable sound chip
EB2F	LDY #&02    ;set and
EB31	DEY         ;execute short delay
EB32	BNE &EB31   ;
EB34	LDY #&08    ;then disable sound chip again
EB36	STY &FE40   ;
EB39	LDY #&04    ;set delay
EB3B	DEY         ;and loop delay
EB3C	BNE &EB3B   ;
EB3E	PLP         ;get back flags
EB3F	RTS         ;and exit

*******: Sound parameters look up table **********************************

EB40	DB  &E0,&C0,&A0,&80


EB44	JMP &EC59   ;just to allow relative branches in early part
    	            ;of sound interrupt routine


*************************************************************************
*                                                                       *
*       PROCESS SOUND INTERRUPT                                         *
*                                                                       *
*************************************************************************

EB47	LDA #&00    ;
EB49	STA &083B   ;zero number of channels on hold for sync
EB4C	LDA &0838   ;get number of channels required for sync
EB4F	BNE &EB57   ;if this <>0 then EB57
EB51	INC &083B   ;else number of chanels on hold for sync =1
EB54	DEC &0838   ;number of channels required for sync =255

EB57	LDX #&08    ;set loop counter
EB59	DEX         ;loop
EB5A	LDA &0800,X ;get value of &800 +offset (sound queue occupancy)
EB5D	BEQ &EB44   ;if 0 goto EC59 no sound this channel
EB5F	LDA &02CF,X ;else get buffer busy flag
EB62	BMI &EB69   ;if negative (buffer empty) goto EB69
EB64	LDA &0818,X ;else if duration count not zer0
EB67	BNE &EB6C   ;goto EB6C
EB69	JSR &EC6B   ;check and pick up new sound if required
EB6C	LDA &0818,X ;if duration count 0
EB6F	BEQ &EB84   ;goto EB84
EB71	CMP #&FF    ;else if it is &FF (infinite duration)
EB73	BEQ &EB87   ;go onto EB87
EB75	DEC &081C,X ;decrement 10 mS count
EB78	BNE &EB87   ;and if 0
EB7A	LDA #&05    ;reset to 5
EB7C	STA &081C,X ;to give 50 mSec delay
EB7F	DEC &0818,X ;and decrement main counter
EB82	BNE &EB87   ;if not zero then EB87
EB84	JSR &EC6B   ;else check and get nw sound
EB87	LDA &0824,X ;if step progress counter is 0 no envelope involved
EB8A	BEQ &EB91   ;so jump to EB91
EB8C	DEC &0824,X ;else decrement it
EB8F	BNE &EB44   ;and if not zero go on to EC59
EB91	LDY &0820,X ;get  envelope data offset from (8C0)
EB94	CPY #&FF    ;if 255 no envelope set so
EB96	BEQ &EB44   ;goto EC59
EB98	LDA &08C0,Y ;else get get step length
EB9B	AND #&7F    ;zero repeat bit
EB9D	STA &0824,X ;and store it
EBA0	LDA &0808,X ;get phase counter
EBA3	CMP #&04    ;if release phase completed
EBA5	BEQ &EC07   ;goto EC07
EBA7	LDA &0808,X ;else start new step by getting phase
EBAA	CLC         ;
EBAB	ADC &0820,X ;add it to interval multiplier
EBAE	TAY         ;transfer to Y
EBAF	LDA &08CB,Y ;and get target value base for envelope
EBB2	SEC         ;
EBB3	SBC #&3F    ;
EBB5	STA &083A   ;store modified number as current target amplitude
EBB8	LDA &08C7,Y ;get byte from envelope store
EBBB	STA &0839   ;store as current amplitude step
EBBE	LDA &0804,X ;get base volumelevel
EBC1	PHA         ;save it
EBC2	CLC         ;clear carry
EBC3	ADC &0839   ;add to current amplitude step
EBC6	BVC &EBCF   ;if no overflow
EBC8	ROL         ;double it Carry = bit 7
EBC9	LDA #&3F    ;if bit =1 A=&3F
EBCB	BCS &EBCF   ;into &EBCF
EBCD	EOR #&FF    ;else toggle bits (A=&C0)

    	            ;at this point the BASIC volume commands are converted
    	            ; &C0 (0) to &38 (-15) 3 times, In fact last 3 bits
    	            ;are ignored so &3F represents -15

EBCF	STA &0804,X ;store in current volume
EBD2	ROL         ;multiply by 2
EBD3	EOR &0804,X ;if bits 6 and 7 are equal
EBD6	BPL &EBE1   ;goto &EBE1
EBD8	LDA #&3F    ;if carry clear A=&3F (maximum)
EBDA	BCC &EBDE   ;or
EBDC	EOR #&FF    ;&C0 minimum

EBDE	STA &0804,X ;and this is stored in current volume

EBE1	DEC &0839   ;decrement amplitude change per step
EBE4	LDA &0804,X ;get volume again
EBE7	SEC         ;set carry
EBE8	SBC &083A   ;subtract target value
EBEB	EOR &0839   ;negative value undicates correct trend
EBEE	BMI &EBF9   ;so jump to next part
EBF0	LDA &083A   ;else enter new phase
EBF3	STA &0804,X ;
EBF6	INC &0808,X ;

EBF9	PLA         ;get the old volume level
EBFA	EOR &0804,X ;and compare with the old
EBFD	AND #&F8    ;
EBFF	BEQ &EC07   ;if they are the same goto EC07
EC01	LDA &0804,X ;else set new level
EC04	JSR &EB0A   ;via EB0A
EC07	LDA &0810,X ;get absolute pitch value
EC0A	CMP #&03    ;if it =3
EC0C	BEQ &EC59   ;skip rest of loop as all sections are finished
EC0E	LDA &0814,X ;else if 814,X is not 0 current section is not
    	            ;complete
EC11	BNE &EC3D   ;so EC3D
EC13	INC &0810,X ;else implement a section change
EC16	LDA &0810,X ;check if its complete
EC19	CMP #&03    ;if not
EC1B	BNE &EC2D   ;goto EC2D
EC1D	LDY &0820,X ;else set A from
EC20	LDA &08C0,Y ;&820 and &8C0 (first envelope byte)
EC23	BMI &EC59   ;if negative there is no repeat
EC25	LDA #&00    ;else restart section sequence
EC27	STA &0830,X ;
EC2A	STA &0810,X ;

EC2D	LDA &0810,X ;get number of steps in new section
EC30	CLC         ;
EC31	ADC &0820,X ;
EC34	TAY         ;
EC35	LDA &08C4,Y ;
EC38	STA &0814,X ;set in 814+X
EC3B	BEQ &EC59   ;and if 0 then EC59

EC3D	DEC &0814,X ;decrement
EC40	LDA &0820,X ;and pick up rate of pitch change
EC43	CLC         ;
EC44	ADC &0810,X ;
EC47	TAY         ;
EC48	LDA &08C1,Y ;
EC4B	CLC         ;
EC4C	ADC &0830,X ;add to rate of differential pitch change
EC4F	STA &0830,X ;and save it
EC52	CLC         ;
EC53	ADC &080C,X ;ad to base pitch
EC56	JSR &ED01   ;and set new pitch

EC59	CPX #&04    ;if X=4 (last channel)
EC5B	BEQ &EC6A   ;goto EC6A (RTS)
EC5D	JMP &EB59   ;else do loop again

EC60	LDX #&08    ;X=7 again
EC62	DEX         ;loop
EC63	JSR &ECA2   ;clear channel
EC66	CPX #&04    ;if not 4
EC68	BNE &EC62   ;do it again
EC6A	RTS         ;and return
    	            ;
EC6B	LDA &0808,X ;check for last channel
EC6E	CMP #&04    ;is it 4 (release complete)
EC70	BEQ &EC77   ;if so EC77
EC72	LDA #&03    ;else mark release in progress
EC74	STA &0808,X ;and store it
EC77	LDA &02CF,X ;is buffer not empty
EC7A	BEQ &EC90   ;if so EC90
EC7C	LDA #&00    ;else mark buffer not empty
EC7E	STA &02CF,X ;an store it

EC81	LDY #&04    ;loop counter
EC83	STA &082B,Y ;zero sync bytes
EC86	DEY         ;
EC87	BNE &EC83   ;until Y=0

EC89	STA &0818,X ;zero duration count
EC8C	DEY         ;and set sync count to
EC8D	STY &0838   ;&FF
EC90	LDA &0828,X ;get synchronising flag
EC93	BEQ &ECDB   ;if its 0 then ECDB
EC95	LDA &083B   ;else get number of channels on hold
EC98	BEQ &ECD0   ;if 0 then ECD0
EC9A	LDA #&00    ;else
EC9C	STA &0828,X ;zero note length interval
EC9F	JMP &ED98   ;and goto ED98

ECA2	JSR &EB03   ;silence the channel
ECA5	TYA         ;Y=0 A=Y
ECA6	STA &0818,X ;zero main count
ECA9	STA &02CF,X ;mark buffer not empty
ECAC	STA &0800,X ;mark channel dormant
ECAF	LDY #&03    ;loop counter
ECB1	STA &082C,Y ;zero sync flags
ECB4	DEY         ;
ECB5	BPL &ECB1   ;

ECB7	STY &0838   ;number of channels to &FF
ECBA	BMI &ED06   ;jump to ED06 ALWAYS

ECBC	PHP         ;save flags
ECBD	SEI         ;and disable interrupts
ECBE	LDA &0808,X ;check for end of release
ECC1	CMP #&04    ;
ECC3	BNE &ECCF   ;and if not found ECCF
ECC5	JSR &E45B   ;elseexamine buffer
ECC8	BCC &ECCF   ;if not empty ECCF
ECCA	LDA #&00    ;else mark channel dormant
ECCC	STA &0800,X ;
ECCF	PLP         ;get back flags

ECD0	LDY &0820,X ;if no envelope 820=&FF
ECD3	CPY #&FF    ;
ECD5	BNE &ECDA   ;then terminate sound
ECD7	JSR &EB03   ;via EB03
ECDA	RTS         ;else return
    	            ;


************ Synchronise sound routines **********************************

ECDB	JSR &E45B   ;examine buffer if empty carry set
ECDE	BCS &ECBC   ;
ECE0	AND #&03    ;else examine next word if>3 or 0
ECE2	BEQ &EC9F   ;goto ED98 (via EC9F)
ECE4	LDA &0838   ;else get synchronising count
ECE7	BEQ &ECFE   ;in 0 (complete) goto ECFE
ECE9	INC &0828,X ;else set sync flag
ECEC	BIT &0838   ;if 0838 is +ve S has already been set so
ECEF	BPL &ECFB   ;jump to ECFB
ECF1	JSR &E45B   ;else get first byte
ECF4	AND #&03    ;mask bits 0,1
ECF6	STA &0838   ;and store result
ECF9	BPL &ECFE   ;Jump to ECFE (ALWAYS!!)

ECFB	DEC &0838   ;decrement 0838
ECFE	JMP &ECD0   ;and silence the channel if envelope not in use


************ Pitch setting ***********************************************

ED01	CMP &082C,X ;If A=&82C,X then pitch is unchanged
ED04	BEQ &ECDA   ;then exit via ECDA
ED06	STA &082C,X ;store new pitch
ED09	CPX #&04    ;if X<>4 then not noise so
ED0B	BNE &ED16   ;jump to ED16


*********** Noise setting ************************************************

ED0D	AND #&0F    ;convert to chip format
ED0F	ORA &EB3C,X ;
ED12	PHP         ;save flags
ED13	JMP &ED95   ;and pass to chip control routine at EB22 via ED95


ED16	PHA         ;
ED17	AND #&03    ;
ED19	STA &083C   ;lose eigth tone surplus
ED1C	LDA #&00    ;
ED1E	STA &083D   ;
ED21	PLA         ;get back A
ED22	LSR         ;divide by 12
ED23	LSR         ;
ED24	CMP #&0C    ;
ED26	BCC &ED2F   ;
ED28	INC &083D   ;store result
ED2B	SBC #&0C    ;with remainder in A
ED2D	BNE &ED24   ;

    	            ;at this point 83D defines the Octave
    	            ;A the semitone within the octave
ED2F	TAY         ;Y=A
ED30	LDA &083D   ;get octave number into A
ED33	PHA         ;push it
ED34	LDA &EDFB,Y ;get byte from look up table
ED37	STA &083D   ;store it
ED3A	LDA &EE07,Y ;get byte from second table
ED3D	PHA         ;push it
ED3E	AND #&03    ;keep two LS bits only
ED40	STA &083E   ;save them
ED43	PLA         ;pull second table byte
ED44	LSR         ;push hi nybble into lo nybble
ED45	LSR         ;
ED46	LSR         ;
ED47	LSR         ;
ED48	STA &083F   ;store it
ED4B	LDA &083D   ;get back octave number
ED4E	LDY &083C   ;adjust for surplus eighth tones
ED51	BEQ &ED5F   ;
ED53	SEC         ;
ED54	SBC &083F   ;
ED57	BCS &ED5C   ;
ED59	DEC &083E   ;
ED5C	DEY         ;
ED5D	BNE &ED53   ;
ED5F	STA &083D   ;
ED62	PLA         ;
ED63	TAY         ;
ED64	BEQ &ED6F   ;
ED66	LSR &083E   ;
ED69	ROR &083D   ;
ED6C	DEY         ;
ED6D	BNE &ED66   ;
ED6F	LDA &083D   ;
ED72	CLC         ;
ED73	ADC &C43D,X ;
ED76	STA &083D   ;
ED79	BCC &ED7E   ;
ED7B	INC &083E   ;
ED7E	AND #&0F    ;
ED80	ORA &EB3C,X ;
ED83	PHP         ;push P
ED84	SEI         ;bar interrupts
ED85	JSR &EB21   ;set up chip access 1
ED88	LDA &083D   ;
ED8B	LSR &083E   ;
ED8E	ROR         ;
ED8F	LSR &083E   ;
ED92	ROR         ;
ED93	LSR         ;
ED94	LSR         ;
ED95	JMP &EB22   ;set up chip access 2 and return



**************** Pick up and interpret sound buffer data *****************

ED98	PHP         ;push flags
ED99	SEI         ;disable interrupts
ED9A	JSR &E460   ;read a byte from buffer
ED9D	PHA         ;push A
ED9E	AND #&04    ;isolate H bit
EDA0	BEQ &EDB7   ;if 0 then EDB7
EDA2	PLA         ;get back A
EDA3	LDY &0820,X ;if &820,X=&FF
EDA6	CPY #&FF    ;envelope is not in use
EDA8	BNE &EDAD   ;
EDAA	JSR &EB03   ;so call EB03 to silence channel

EDAD	JSR &E460   ;clear buffer of redundant data
EDB0	JSR &E460   ;and again
EDB3	PLP         ;get back flags
EDB4	JMP &EDF7   ;set main duration count using last byte from buffer

EDB7	PLA         ;get back A
EDB8	AND #&F8    ;zero bits 0-2
EDBA	ASL         ;put bit 7 into carry
EDBB	BCC &EDC8   ;if zero (envelope) jump to EDC8
EDBD	EOR #&FF    ;invert A
EDBF	LSR         ;shift right
EDC0	SEC         ;
EDC1	SBC #&40    ;subtract &40
EDC3	JSR &EB0A   ;and set volume
EDC6	LDA #&FF    ;A=&FF

EDC8	STA &0820,X ;get envelope no.-1 *16 into A
EDCB	LDA #&05    ;set duration sub-counter
EDCD	STA &081C,X ;
EDD0	LDA #&01    ;set phase counter
EDD2	STA &0824,X ;
EDD5	LDA #&00    ;set step counter
EDD7	STA &0814,X ;
EDDA	STA &0808,X ;and envelope phase
EDDD	STA &0830,X ;and pitch differential
EDE0	LDA #&FF    ;
EDE2	STA &0810,X ;set step count
EDE5	JSR &E460   ;read pitch
EDE8	STA &080C,X ;set it
EDEB	JSR &E460   ;read buffer
EDEE	PLP         ;
EDEF	PHA         ;save duration
EDF0	LDA &080C,X ;get back pitch value
EDF3	JSR &ED01   ;and set it
EDF6	PLA         ;get back duration
EDF7	STA &0818,X ;set it
EDFA	RTS         ;and return


********************* Pitch look up table 1*****************************
EDFB	    DB         &F0
EDFC	    DB         &B7
EDFD	    DB         &82
EDFE	    DB         &4F
EDFF	    DB         &20
EE00	    DB         &F3
EE01	    DB         &C8
EE02	    DB         &A0
EE03	    DB         &7B
EE04	    DB         &57
EE05	    DB         &35
EE06	    DB         &16


********************* Pitch look up table 2 *****************************

EE07	    DB         &E7
EE08	    DB         &D7
EE09	    DB         &CB
EE0A	    DB         &C3
EE0B	    DB         &B7
EE0C	    DB         &AA
EE0D	    DB         &A2
EE0E	    DB         &9A
EE0F	    DB         &92
EE10	    DB         &8A
EE11	    DB         &82
EE12	    DB         &7A

*********: set current filing system ROM/PHROM **************************
EE13	LDA #&EF    ;get ROM
EE15	STA &F5     ;store it
EE17	RTS         ;return



********** Get byte from data ROM ***************************************

EE18	LDX #&0D    ;X=13
EE1A	INC &F5     ;
EE1C	LDY &F5     ;get Rom
EE1E	BPL &EE59   ;if +ve it's a sideways ROM else it's a PHROM
EE20	LDX #&00    ;PHROM
EE22	STX &F7     ;set address pointer in PHROM
EE24	INX         ;
EE25	STX &F6     ;to 0001
EE27	JSR &EEBB   ;pass info to speech processor
EE2A	LDX #&03    ;X=3

EE2C	JSR &EE62   ;check for speech processor and output until
    	            ;it reports, read byte from ROM
EE2F	CMP &DF0C,X ;if A<> DF0C+X then EE18 (DF0C = (C))
EE32	BNE &EE18   ;
EE34	DEX         ;else decrement X
EE35	BPL &EE2C   ;and do it again
EE37	LDA #&3E    ;
EE39	STA &F6     ;get noe lo byte address
EE3B	JSR &EEBB   ;pass info to speech processor
EE3E	LDX #&FF    ;
EE40	JSR &EE62   ;check for speech proc. etc.
EE43	LDY #&08    ;
EE45	ASL         ;
EE46	ROR &F7,X   ;
EE48	DEY         ;
EE49	BNE &EE45   ;
EE4B	INX         ;
EE4C	BEQ &EE40   ;
EE4E	CLC         ;
EE4F	BCC &EEBB   ;


************ ROM SERVICE ************************************************

EE51	LDX #&0E    ;
EE53	LDY &F5     ;if Y is negative (PHROM)
EE55	BMI &EE62   ;GOTO EE62
EE57	LDY #&FF    ;else Y=255
EE59	PHP         ;push flags
EE5A	JSR &F168   ;offer paged rom service
EE5D	PLP         ;pull processor flags
EE5E	CMP #&