.MCALL	.MODULE
.MODULE	RDBLK,VERSION=05,COMMENT=<Read block>

; Copyright (c) 1998 by Mentec, Inc., Nashua, NH.
; All rights reserved
;
; This software is furnished under a license for use only on a
; single computer system and  may  be  copied  only  with  the
; inclusion of the above copyright notice.  This software,  or
; any other copies thereof, may not be provided  or  otherwise
; made available to any other person except for  use  on  such
; system and to one who agrees to these license  terms.  Title
; to  and  ownership of the software shall at all times remain
; in Mentec, Inc.
;
; The information in this document is subject to change without
; notice and should not be construed as a commitment by Digital
; Equipment Corporation, or Mentec, Inc.
;
; Digital and Mentec  assume  no  responsibility for the use or
; reliability of its software on equipment which is not supplied
; by Digital  or Mentec,  and listed  in the  Software  Product
; Description.
.ENABL	GBL,LC

	.SBTTL	Macro definitions

	.MCALL	.READW
	.MCALL	FDBDF$, FERDF$, DEFIN$, RT5DF$

	FDBDF$				;Define FDB offsets
	FERDF$				;Define file service error codes
	DEFIN$				;Definitions for IND files
	RT5DF$				;Definition of ERRBYT

	.PSECT	$RDBLK
	.SBTTL	$RDBLK - Read logical block

;+
;$RDBLK
;This routine reads a logical block from the specified file/device.
;
;Input:  R1 = Address of FDB
;	 R3 = Block number to read
;	 R4 = Address of buffer
;	 R5 = Size of buffer in bytes
;
;Output: R1 = Address of FDB
;	 R3 = Block number read
;	 R4 = Address of buffer
;	 R5 = Size of buffer in bytes
;	 C-bit set if error
;-

	.ENABL	LSB

$RDBLK::SAVE	<R0,R5>
	CMP	R3,F$BLKM(R1)		;Is the block number past end-of-file?
	BHIS	20$			;Yes
				.ASSUME  F$CHAN EQ 0	;F$CHAN(R1)
	ASR	R5			;Convert byte count to words
	.READW	#EMTBLK,@R1,R4,R5,R3 	;Read a block from the file
	BCS	10$			;Branch if error
	MOV	R3,F$BLKN(R1)		;Save block number
	MOV	#<IS.SUC>,R0		;Indicate success
	BR	40$			;Return to caller

10$:	MOV	#<IE.RER>,R0		;Assume read error
	TSTB	@#ERRBYT		;Was it by chance EOF?
	BNE	30$			;Branch if not

20$:	MOV	#<IE.EOF>,R0		;End-of-file detected
30$:	SEC				;Set C-bit to indicate error
40$:	MOV	R0,F$ERR(R1)		;Save the error code
	RESTOR	<R5,R0>
	RETURN
 
	.DSABL	LSB

	.END