10	! ----- CTRL_C_Y_TRAP.FUN -----
	!
	! ----- ENABLES CTRL/C AND CTRL/Y AST-TRAPPING ROUTINE -----
	!
	! ----- 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. -----
	! -----   2) The calling routine must include the ASTMAP map so -----
	! -----      that the EXIT_PROGRAM_FLAG variable is available. -----
	! -----   3) AST_ROUTINE.FUN must be compiled and linked into -----
	! -----      the calling program. -----
	!
	SUB CTRL_C_Y_TRAP

	OPTION TYPE = EXPLICIT			! ENSURE ALL VARIABLES DECLARED

	DECLARE LONG CONSTANT TRUE = (1% = 1%)
	DECLARE LONG CONSTANT FALSE = NOT TRUE

	! ----- SYSTEM SERVICE ERROR CODES AND FUNCTION VALUES -----
	EXTERNAL LONG CONSTANT IO$_SETMODE	! QIOW VALUE FOR MODE SETTING
	EXTERNAL LONG CONSTANT IO$M_OUTBAND	! QIOW VALUE FOR OUT-OF-BAND AST

	RECORD CHARACTER_MASK			! OUT-OF-BAND AST CHARACTER MASK
		LONG MUST_BE_ZERO
		LONG OUT_OF_BAND_CHAR
	END RECORD CHARACTER_MASK

	DECLARE WORD QIO_CHNL			! CHANNEL NUMBER FOR QIOW
	DECLARE LONG QIO_FUNC			! QIOW FUNCTION VALUE
	DIM WORD QIO_IOSB(3%)			! QIOW STATUS BLOCK
	DECLARE CHARACTER_MASK QIO_MASK		! OUT-OF-BAND AST CHARACTER MASK
	DECLARE LONG SYS_STATUS			! SYSTEM SERVICE EXIT STATUS

	EXTERNAL LONG AST_ROUTINE		! OUT-OF-BAND AST HANDLER
	EXTERNAL LONG FUNCTION LIB$STOP(LONG BY				&
		VALUE)				! STOP PROGRAM
	EXTERNAL LONG FUNCTION SYS$ASSIGN	! ASSIGN I/O CHANNEL
	EXTERNAL LONG FUNCTION SYS$QIOW		! QUEUE I/O REQUEST AND WAIT

	! ----- MAPPED VARIABLE FOR AST_ROUTINE FUNCTION -----
	! ----- (MUST ALSO BE DEFINED IN THE CALLING PROGRAM) -----
	MAP (ASTMAP)	WORD EXIT_PROGRAM_FLAG	! TRUE TO EXIT PROGRAM

	EXIT_PROGRAM_FLAG = FALSE		! INIT FLAG FOR END PROGRAM

	! ----- ENABLE OUT-OF-BAND ASYNCHRONOUS SYSTEM TRAP (AST) TO -----
	! ----- ESTABLISH AN AST ROUTINE THAT RESPONDS TO CONTROL/C -----
	! ----- AND CONTROL/Y -----

	SYS_STATUS = SYS$ASSIGN("TT",QIO_CHNL,,)! ASSIGN A CHANNEL TO TERMINAL
	SYS_STATUS = LIB$STOP(SYS_STATUS) IF (SYS_STATUS AND 1%) = 0%

	QIO_FUNC = IO$_SETMODE OR IO$M_OUTBAND	! INITIALIZE QIOW FUNCTION CODE
	QIO_MASK::MUST_BE_ZERO = 0%		! INIT MASK
	QIO_MASK::OUT_OF_BAND_CHAR = 2% ** 3% OR			&
		2% ** 25%			! INIT MASK TO ENABLE CTRL/C AND
						! CTRL/Y (BIT NUMBER = BINARY
						! VALUE OF THE CONTROL
						! CHARACTER)

	! ----- CALL THE QIOW SERVICE TO ENABLE THE OUT-OF-BAND AST. -----
	! ----- NOTE THAT OUT-OF-BAND ASTS ARE REPEATING ASTS; THEY -----
	! ----- CONTINUE TO BE DELIVERED UNTIL SPECIFICALLY DISABLED. -----
	SYS_STATUS = SYS$QIOW(, QIO_CHNL BY VALUE,			&
		QIO_FUNC BY VALUE,					&
		QIO_IOSB() BY REF, , ,					&
		AST_ROUTINE BY REF,					&
		QIO_MASK BY REF, , , ,)
	SYS_STATUS = QIO_IOSB(0%) IF (SYS_STATUS AND 1%) = 1%
	SYS_STATUS = LIB$STOP(SYS_STATUS) IF (SYS_STATUS AND 1%) = 0%

	! ----- NOW, WHENEVER A CTRL/C OR CTRL/Y KEY IS PRESSED, -----
	! ----- INSTEAD OF THE PROGRAM BEING INTERRUPTED, THE VALUE OF -----
	! ----- EXIT_PROGRAM_FLAG WILL BE CHANGED FROM FALSE TO TRUE. -----
	! ----- THE CALLING PROGRAM CAN THEN TEST ITS VALUE WHENEVER IT -----
	! ----- NEEDS TO DO SO. -----

	END SUB