Initial commit.

atari/disk.src

@@ -0,0 +1,179 @@
+	PAGE
+	SBTTL "--- DISK ACCESS: ATARI ---"
+
+	; --------------------
+	; READ A VIRTUAL BLOCK
+	; --------------------
+
+	; ENTRY: TARGET V-BLOCK IN [DBLOCK]
+	;   	 TARGET RAM PAGE IN [DBUFF]
+	; EXIT: CARRY CLEAR IF OKAY, SET IF NOT
+
+GETDSK:	CLD
+	LDA	#1		; V-BLOCKS ALWAYS COME
+	STA	DRIVE		; FROM DRIVE #1
+
+	; CALCULATE SECTOR OF [DBLOCK]
+
+	LDX	DBLOCK+LO	; COPY LSB OF [DBLOCK]
+	STX	SECTOR+LO	; INTO [SECTOR]
+
+	LDA	DBLOCK+HI
+	AND	#%00000001	; MASK ALL BUT BIT 1
+	STA	SECTOR+HI
+	BNE	INPURE		; BLOCK IS PURE IF MSB <> 0
+
+	CPX	ZPURE		; ELSE CHECK LSB
+	BCS	INPURE		; PURE IF >= [ZPURE]
+
+	; HANDLE A PRELOAD BLOCK
+
+	ASL	SECTOR+LO	; MULTIPLY BY 2
+	ROL	SECTOR+HI	; FOR ATARI 128-BYTE SECTORS
+
+	LDA	SECTOR+LO
+	CLC
+	ADC	#73		; ADD DISK PRELOAD OFFSET
+	STA	SECTOR+LO
+	BCC	RDISK
+	INC	SECTOR+HI
+	BNE	RDISK		; AND READ THE SECTOR
+
+	; HANDLE A PURE BLOCK
+
+INPURE:	LDA	SECTOR+LO
+	SEC			; STRIP OFF THE
+	SBC	ZPURE		; VIRTUAL PRELOAD OFFSET
+	STA	SECTOR+LO
+	BCS	INP0
+	DEC	SECTOR+HI
+
+INP0:	ASL	SECTOR+LO	; MULTIPLY BY 2
+	ROL	SECTOR+HI	; FOR ATARI 128-BYTE SECTORS
+
+	INC	SECTOR+LO	; DISK "PURE" OFFSET IS 1
+	BNE	RDISK
+	INC	SECTOR+HI
+
+	; FALL THROUGH ...
+
+	; -----------------
+	; READ A DISK BLOCK
+	; -----------------
+
+	; ENTRY: TARGET SECTOR IN [SECTOR]
+	;	 TARGET DRIVE IN [DRIVE]
+	;	 PAGE TO READ IN [DBUFF]
+	; EXIT: CARRY CLEAR IF OKAY, SET IF NOT
+
+RDISK:	LDA	#$52		; "READ" COMMAND
+	JSR	DODISK		; GET DATA INTO [IOBUFF]
+	BCS	IOERR		; SOMETHING WRONG IF CARRY SET
+
+	LDY	#0		; MOVE DATA IN [IOBUFF]
+RDSK0:	LDA	IOBUFF,Y	; TO [DBUFF]
+	STA	(DBUFF),Y
+	INY
+	BNE	RDSK0
+
+	BEQ	SNEXT		; UPDATE & RETURN
+
+	; ------------------
+	; WRITE A DISK BLOCK
+	; ------------------
+
+	; ENTRY: TARGET SECTOR IN [SECTOR]
+	;	 TARGET DRIVE IN [DRIVE]
+	;	 PAGE TO WRITE IN [DBUFF]
+	; EXIT: CARRY CLEAR IF OKAY, SET IF NOT
+
+PUTDSK:	LDY	#0		; MOVE THE PAGE
+PDSK0:	LDA	(DBUFF),Y	; AT [DBUFF]
+	STA	IOBUFF,Y	; INTO [IOBUFF]
+	INY
+	BNE	PDSK0
+
+	LDA	#$57		; "WRITE" COMMAND
+	JSR	DODISK
+	BCS	IOERR		; SOMETHING WRONG IF CARRY SET
+
+SNEXT:	INC	DBUFF+HI	; POINT TO NEXT RAM PAGE
+
+	INC	DBLOCK+LO	; NEXT V-PAGE
+	BNE	SNX0
+	INC	DBLOCK+HI
+
+SNX0:	INC	SECTOR+LO	; AND NEXT SECTOR
+	BNE	SNX1
+	INC	SECTOR+HI
+
+SNX1:	CLC			; CLEAR CARRY FOR SUCCESS
+
+IOERR:	RTS			; ELSE RETURN WITH CARRY SET
+
+	; ---------------
+	; ACCESS THE DISK
+	; ---------------
+
+	; ENTRY: [A] = $52 TO READ, $57 TO WRITE
+	;	 [DRIVE] = TARGET DRIVE (1 OR 2)
+	;	 [SECTOR] = TARGET SECTOR
+	; EXIT: CARRY CLEAR IF OKAY, SET IF NOT
+
+DODISK:	STA	DCOMND		; SET READ/WRITE COMMAND
+
+	LDA	DRIVE		; SPECIFY
+	STA	DUNIT		; WHICH DRIVE TO USE
+
+	; CHECK VALIDITY OF SECTOR RANGE
+
+	LDX	SECTOR+LO	; GET LSB AND
+	LDA	SECTOR+HI	; MSB OF TARGET SECTOR
+	CMP	#$02		; MSB WITHIN RANGE?
+	BCC	RANOK		; OKAY IF < 2
+	BNE	RANERR		; RANGE ERROR IF > 2
+	CPX	#$D0		; IF MSB WAS $02, IS LSB < $CF?
+	BCS	RANERR		; ERROR IF NOT
+
+RANOK:	STX	DAUX1		; TELL SIO
+	STA	DAUX2		; WHICH SECTOR TO USE
+
+	LDA	#LOW IOBUFF	; POINT TO
+	STA	DBUFLO		; THE BOTTOM HALF
+	LDA	#HIGH IOBUFF	; OF [IOBUFF]
+	STA	DBUFHI
+
+	JSR	DSKINV		; ACCESS 1ST HALF OF [IOBUFF]
+	LDA	DSTATS		; CHECK STATUS
+	BMI	DERR		; ERROR IF NEGATIVE
+
+	INC	SECTOR+LO	; POINT TO NEXT SECTOR
+	BNE	DDSK0
+	INC	SECTOR+HI
+
+DDSK0:	LDA	SECTOR+LO	; UPDATE [DAUX1/2]
+	STA	DAUX1
+	LDA	SECTOR+HI
+	STA	DAUX2
+
+	LDA	#LOW BUFTOP	; POINT TO TOP HALF
+	STA	DBUFLO		; OF [IOBUFF]
+	LDA	#HIGH BUFTOP
+	STA	DBUFHI
+
+	JSR	DSKINV		; ACCESS TOP HALF OF [IOBUFF]
+	LDA	DSTATS		; CHECK STATUS
+	BMI	DERR		; ERROR IF NEGATIVE
+	CLC			; CLEAR CARRY FOR NO ERRORS
+	RTS
+
+DERR:	SEC			; OR SET IT IF ERROR
+	RTS
+
+	; *** ERROR #12: DISK ADDRESS OUT OF RANGE ***
+
+RANERR:	LDA	#12
+	JMP	ZERROR
+
+	END
+