10	! ----- WRITE_ATTN_AST.FUN -----
	SUB WRITE_ATTN_AST(LONG PARAM, LONG RZERO, LONG RONE, LONG PC, LONG PSL)
	!
	! This subroutine is called as an AST procedure from SEND_OPER_MSG.FUN
	!
	! It reads and then discards the message that was written to our
	! mailbox
	!
	! NOTE:  The five parameters coded on the SUB statement are required
	! when coding any AST routine in BASIC.  These are the arguments passed
	! by the system on entry to the AST service routine.  Although they are
	! not used in this routine, BASIC checks the argument count and they
	! must be present.
	!
	! ----- Last Change 05/01/89 by Brian Lomasky -----
	!
	! ----- Teradyne, Inc., 179 Lincoln Street, Boston, MA  02111 -----
	! ----- (617) 482-2706, x3259 -----
	!
	! ----- Neither Brian Lomasky nor Teradyne, Inc. implicitly or -----
	! ----- explicitly implies this program is usable in any way. -----
	! ----- This program is released to the public domain in an -----
	! ----- "AS-IS" condition. -----
	!
	! ----- Restrictions: -----
	! -----   1) Requires VAX BASIC V2.4 or later. -----
	!
	OPTION TYPE = EXPLICIT

	EXTERNAL LONG CONSTANT IO$_READVBLK	! QIO READ VIR BLOCK FUNC CODE
	EXTERNAL LONG CONSTANT IO$M_NOW		! QIO COMPLETE IMMEDIATELY CODE

	! ----- VARIABLE DECLARATIONS -----
	DECLARE BYTE DUMMY_BUFFER		! QIOW READ VIRTUAL BLOCK BUFFER
	DECLARE LONG FUNC			! QIOW FUNCTION CODE
	DIM WORD IOSB(3%)			! QIOW I/O STATUS BLOCK
	DECLARE LONG SYS_STATUS			! SYSTEM SERVICE EXIT STATUS

	! ----- MAPPED VARIABLE FOR PASSING MAILBOX I/O CHANNEL -----
	MAP (MBXCHAN) WORD MAILBOX_CHNL		! I/O CHANNEL FOR MAILBOX QIO

	EXTERNAL SUB LIB$STOP			! ABORT PROCESS WITH STATUS
	EXTERNAL LONG FUNCTION SYS$QIOW		! QUEUE I/O REQUEST AND WAIT

	! ----- READ ANY MESSAGE THAT WAS SENT TO OUR MAILBOX -----
	FUNC = IO$_READVBLK OR IO$M_NOW
	SYS_STATUS = SYS$QIOW( ,		! EVENT FLAG		&
		MAILBOX_CHNL BY VALUE,		! DEVICE I/O CHANNEL	&
		FUNC BY VALUE,			! DEVICE FUNCTION CODE	&
		IOSB() BY REF,			! I/O STATUS BLOCK	&
		,				! AST ADDRESS		&
		,				! AST PARAMETER		&
		DUMMY_BUFFER BY REF,		! READ VIRT BLOCK BUFFER&
		1% BY VALUE,			! SIZE OF READ BUFFER	&
		,				! AST ACCESS MODE	&
		,				! <N/A>			&
		,				! <N/A>			&
		)				! <N/A>

	! ----- IGNORE ANY ERRORS THAT MAY OCCUR FROM THE SYS$QIOW CALL -----
	!CALL LIB$STOP(SYS_STATUS BY VALUE) IF (SYS_STATUS AND 1%) = 0%
	!CALL LIB$STOP(IOSB(0%) BY VALUE) IF (IOSB(0%) AND 1%) = 0%

	END SUB