Initial commit.

atari/paging.src

@@ -0,0 +1,239 @@
+	PAGE
+	SBTTL	"--- TIME-STAMP PAGING ROUTINE ---"
+
+	; -------------------------
+	; FETCH NEXT BYTE OF Z-CODE
+	; -------------------------
+
+	; EXIT: BYTE AT [ZPC] IN [A] & [Y]; FLAGS SET
+
+NEXTPC:	LDA	ZPCFLG		; IS [ZPCPNT] VALID?
+	BNE	NPC2		; YES, GET THE BYTE
+
+	; Z-PAGE HAS CHANGED!
+
+	LDA	ZPCM		; GET TOP
+	LDY	ZPCH		; 9 BITS OF [ZPC]
+	BNE	NPC0		; SWAP PAGE IF TOP BIT IS SET
+
+	CMP	ZPURE		; IS THIS PAGE PRELOADED?
+	BCS	NPC0		; NO, SWAP IT IN
+
+	ADC	ZCODE		; ELSE MAKE IT ABSOLUTE
+	BNE	NPC1		; AND GIVE IT TO [ZPCPNT]
+
+NPC0:	LDX	#0
+	STX	MPCFLG		; INVALIDATE [MPC]
+	JSR	PAGE		; AND GET ABS PAGE ADDR INTO [A]
+
+NPC1:	STA	ZPCPNT+HI	; SET ABS PAGE ADDRESS
+	LDX	#$FF
+	STX	ZPCFLG		; VALIDATE [ZPCPNT]
+	INX			; = 0
+	STX	ZPCPNT+LO	; CLEAR LSB OF POINTER
+
+NPC2:	LDY	ZPCL		; FETCH PAGE INDEX
+	LDA	(ZPCPNT),Y	; GET Z-BYTE
+
+	INC	ZPCL		; END OF PAGE YET?
+	BNE	NPC3		; NO, EXIT
+
+	LDY	#0
+	STY	ZPCFLG		; ELSE INVALIDATE [ZPCPNT]
+
+	INC	ZPCM		; POINT [ZPC] TO
+	BNE	NPC3		; THE NEXT
+	INC	ZPCH		; Z-PAGE
+
+NPC3:	TAY			; SET FLAGS
+	RTS			; AND RETURN
+
+	; -------------------------------
+	; GET NEXT BYTE OF VIRTUAL MEMORY
+	; -------------------------------
+
+	; EXIT: BYTE AT [MPC] IN [A] & [Y]; FLAGS SET
+
+GETBYT:	LDA	MPCFLG		; IS [MPCPNT] VALID?
+	BNE	GTBT2		; YES, GET THE BYTE
+
+	; Z-PAGE HAS CHANGED!
+
+	LDA	MPCM		; GET TOP
+	LDY	MPCH		; 9 BITS OF [MPC]
+	BNE	GTBT0		; SWAP PAGE IF TOP BIT IS SET
+
+PATCH	EQU	$+1		; PATCH POINT FOR "VERIFY"
+
+	CMP	ZPURE		; IS THIS PAGE PRELOADED?
+	BCS	GTBT0		; NO, SWAP IT IN
+
+	ADC	ZCODE		; ELSE MAKE IT ABSOLUTE
+	BNE	GTBT1		; AND GIVE IT TO [MPCPNT]
+
+GTBT0:	LDX	#0
+	STX	ZPCFLG		; INVALIDATE [ZPC]
+	JSR	PAGE		; AND GET ABS PAGE ADDR INTO [A]
+
+GTBT1:	STA	MPCPNT+HI	; SET ABS PAGE ADDRESS
+	LDX	#$FF
+	STX	MPCFLG		; VALIDATE [MPCPNT]
+	INX			; = 0
+	STX	MPCPNT+LO	; CLEAR LSB OF POINTER
+
+GTBT2:	LDY	MPCL		; FETCH PAGE INDEX
+	LDA	(MPCPNT),Y	; GET Z-BYTE
+
+	INC	MPCL		; END OF PAGE YET?
+	BNE	GTBT3		; NO, EXIT
+
+	LDY	#0
+	STY	MPCFLG		; ELSE INVALIDATE [MPCPNT]
+
+	INC	MPCM		; POINT [MPC] TO
+	BNE	GTBT3		; THE NEXT
+	INC	MPCH		; Z-PAGE
+
+GTBT3:	TAY			; SET FLAGS
+	RTS			; AND RETURN
+
+	; ------------------------
+	; LOCATE A SWAPABLE Z-PAGE
+	; ------------------------
+
+	; ENTRY: TARGET Z-PAGE IN [A/Y] (9 BITS)
+	; EXIT: ABSOLUTE PAGE IN [A]
+
+PAGE:	STA	TARGET+LO	; SAVE THE
+	STY	TARGET+HI	; TARGET Z-PAGE HERE
+
+	; IS THIS Z-PAGE ALREADY PAGED IN?
+
+	LDX	#0
+	STX	ZPAGE		; START AT BUFFER #0
+
+PG1:	CMP	PTABL,X		; LSB MATCHED?
+	BNE	PG2		; NO, TRY NEXT BUFFER
+	TYA			; ELSE CHECK
+	CMP	PTABH,X		; TOP BIT
+	BEQ	PG4		; MATCHED! BUFFER IN [ZPAGE]
+	LDA	TARGET+LO	; ELSE RESTORE LSB
+PG2:	INC	ZPAGE		; UPDATE TALLY
+	INX
+	CPX	PMAX		; OUT OF BUFFERS YET?
+	BCC	PG1		; NO, KEEP SEARCHING
+
+	; SWAP IN THE TARGET PAGE
+
+PG3:	JSR	EARLY		; GET EARLIEST PAGE
+	LDX	SWAP		; INTO [SWAP] & [X]
+	STX	ZPAGE		; SAVE FOR LATER
+
+	LDA	TARGET+LO	; ASSIGN THE TARGET PAGE
+	STA	PTABL,X		; TO THE EARLIEST BUFFER
+	STA	DBLOCK+LO	; ALSO GIVE IT TO ZDOS
+
+	LDA	TARGET+HI	; SAME FOR TOP BIT
+	AND	#%00000001	; USE ONLY BIT 0
+	STA	PTABH,X
+	STA	DBLOCK+HI
+
+	TXA
+	CLC
+	ADC	PAGE0		; CALC ABS ADDR OF BUFFER
+	STA	DBUFF+HI	; GIVE IT TO ZDOS
+
+	JSR	GETDSK		; SWAP IN THE NEW PAGE
+	BCS	DSKERR		; ERROR IF CARRY SET
+
+	; UPDATE THE TIMESTAMP
+
+PG4:	LDY	ZPAGE		; GET THE BUFFER INDEX
+	LDA	LRUMAP,Y	; GET THIS BUFFER'S STAMP
+	CMP	STAMP		; SAME AS CURRENT STAMP?
+	BEQ	PG8		; YES, EXIT
+
+	INC	STAMP		; UPDATE STAMP
+	BNE	PG7		; CONTINUE IF NO OVERFLOW
+
+	; HANDLE STAMP OVERFLOW
+
+	JSR	EARLY		; GET EARLIEST STAMP INTO [LRU]
+
+	LDX	#0		; INIT INDEX
+PG5:	LDA	LRUMAP,X	; GET A STAMP READING
+	BEQ	PG6		; EXIT IF ALREADY ZERO
+	SEC			; ELSE SUBTRACT OFF
+	SBC	LRU		; THE EARLIEST TIMESTAMP
+	STA	LRUMAP,X	; AND REPLACE THE STAMP
+PG6:	INX
+	CPX	PMAX		; END OF SWAPPING SPACE?
+	BCC	PG5		; LOOP TILL ALL STAMPS FIXED
+
+	LDA	#0		; TURN BACK THE CLOCK
+	SEC			; TO REFLECT NEW
+	SBC	LRU		; STAMP READING
+	STA	STAMP
+
+PG7:	LDA	STAMP		; FETCH STAMP
+	STA	LRUMAP,Y	; STAMP TARGET PAGE WITH IT
+
+PG8:	LDA	ZPAGE		; GET BUFFER INDEX
+	CLC			; MAKE IT
+	ADC	PAGE0		; ABSOLUTE
+	RTS			; AND RETURN IT IN [A]
+
+	; *** ERROR #14: DRIVE ACCESS ***
+
+DSKERR:	LDA	#14
+	JMP	ZERROR
+
+	; -------------------------
+	; LOCATE EARLIEST TIMESTAMP
+	; -------------------------
+
+	; EXIT: [LRU] - EARLIEST TIMESTAMP
+	;	[SWAP] = INDEX TO EARLIEST BUFFER
+
+EARLY:	LDX	#0		; INIT INDEX
+	STX	SWAP		; AND [SWAP]
+	LDA	LRUMAP		; GET STAMP OF BUFFER #0
+	INX			; START COMPARE WITH BUFFER #1
+EAR0:	CMP	LRUMAP,X	; IS THIS STAMP EARLIER THAN [A]?
+	BCC	EAR1		; NO, TRY NEXT STAMP
+	LDA	LRUMAP,X	; ELSE FETCH EARLIER ENTRY
+	STX	SWAP		; AND REMEMBER WHERE WE FOUND IT
+EAR1:	INX			; POINT TO NEXT STAMP
+	CPX	PMAX		; OUT OF STAMPS YET?
+	BCC	EAR0		; LOOP TILL EMPTY
+
+	STA	LRU		; SAVE EARLIEST STAMP HERE
+	RTS
+
+	; -------------------------
+	; POINT [MPC] TO V-ADDR [I]
+	; -------------------------
+
+SETWRD:	LDA	I+LO
+	STA	MPCL
+	LDA	I+HI
+	STA	MPCM
+
+	LDA	#0
+	STA	MPCH		; ZERO TOP BIT
+	STA	MPCFLG		; INVALIDATE [MPC]
+	RTS
+
+	; ----------------------------
+	; GET Z-WORD AT [MPC] INTO [I]
+	; ----------------------------
+
+GETWRD:	JSR	GETBYT
+	STA	I+HI
+	JSR	GETBYT
+	STA	I+LO
+	RTS
+
+	END
+
+