; RDDISK -- Subroutine for reading a disk - block by block
;
;	Synanon Church
;	Mike Vandeman
;	May 20, 1983
;	
;
;MAP1 BLOCK'NUMBER,B,4
;MAP1 BUFFER'ADDRESS,B,4
;MAP1 DISK'NUMBER,B,2
;MAP1 ERROR'CODE,B,1
;MAP1 INPUT'BUFFER,X,512
;
;INPUT "DISK? ", DISK'NUMBER
;INPUT "BLOCK #? ", BLOCK'NUMBER
;
;XCALL RDDISK, DISK'NUMBER, BLOCK'NUMBER, INPUT'BUFFER, BUFFER'ADDRESS, &
;    ERROR'CODE

	OBJNAM	RDDISK.SBR		;assemble with this name
	SEARCH 	SYS
	SEARCH	SYSSYM
	RADIX	10			;use decimal arithmetic
	PHDR	-1,PV$RSM,PH$REU

START:	LEA	A0,DDB
	MOV	34(A3),A1		;return buffer address
	MOVW	24(A3),2(A1)		;move high order word
	MOVW	26(A3),@A1		;move low order word
	ANDB	#D$INI,D.FLG(A0)	;DDB initialized?
	BNE	READ			;yes, set up for the read
	ORB	#D$ERC,D.FLG(A0)	;return even if errors	
	MOVW	#[DSK],D.DEV(A0)	;device: "DSK"
	MOV	#512,D.SIZ(A0)		;default buffer size
	ORB	#D$INI,D.FLG(A0)	;indicate DDB is initialized
READ:	MOV	4(A3),A1		;get address of driver
	MOVW	@A1,D.DVR(A0)		;enter driver # in DDB
	MOV	14(A3),A1		;get address of block #
	MOVW	@A1,D.REC+2(A0)		;enter physical record # in DDB (low order word)
	MOVW	2(A1),D.REC(A0)		;enter physical record # in DDB (high order word)
	MOV	24(A3),D.BUF(A0)	;enter buffer address in DDB
	CLRB	D.ERR(A0)		;clear errors and flags
	READ	@A0			;read disk block
	MOV	44(A3),A1		;return error code
	MOVB	D.ERR(A0),@A1		;return error code
	RTN

	EVEN
DDB:	BLKB	D.DDB
	END

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