.TITLE	MBDADR - COMPUTE AN MBD ADDRESS
	.IDENT	/04MAY7/	;10:25:00, EM
;	.ENTRY	MBDADR - COMPUTE AN MBD ADDRESS
;+
; M B D A D R
;
; PURPOSE:	COMPUTE AN MBD ADDRESS BASED ON USER-MODE
;		ASR'S. ASSUMES I/O PAGE MAPPED INTO ITSELF
;
; INTERFACE:	CALLING SEQUENCE:  
;			CALL MBDADR
;
;		INPUT:	R5 -- VIRTUAL ADDRESS
;
;		OUTPUT:	R5 -- MBD (16-BIT PHYSICAL WORD ADR) ADDRESS
;
; LANGUAGE:	MACRO-11
;
; RESTRICTIONS:	NOT FORTRAN-CALLABLE
;		THIS ROUTINE CAN BE USED ONLY BY A PRIVILEGED TASK.
;-
; REVISIONS:
; 04-MAY-77	EM	UPDATED TO CONFORM TO STANDARDS
;
;MACRO CALLS
	.MCALL RETURN
;
;I/O PAGE REGISTERS
PAR0=177640
;
MBDADR::
	MOV	R4,-(SP)	;SAVE R4
	MOV	R5,R4	;COPY VIRTUAL ADDRESS
	ASH	#-12.,R4	;HIGH 3 BITS OF ADDRESS IN R4,BITS 1-3
	BIC	#177761,R4	;MASK OUT GARBAGE
	ADD	#PAR0,R4	;(R4)=ADDRESS OF PAR TO USE
	MOV	@R4,R4	;(R4)=CONTENTS OF SELECTED PAR
	ASH	#5,R4
	ASH	#-1,R5	;(R5)=VIRTUAL WORD ADDRESS
	BIC	#170000,R5	;MASK OUT APF FIELD
	ADD 	R4,R5	;R5 NOW HAS MBD ADDRESS
	MOV	(SP)+,R4	;RECOVER R4
	RETURN
.END