From:	CSBVAX::MRGATE!info-vax-RELAY@KL.SRI.COM@SMTP 13-JUN-1988 12:42
To:	ARISIA::EVERHART
Subj:	Trapping broadcast messages


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Date:	  Thu, 9 Jun 88 08:38:27 PDT
From:     KARNEY%PPC.MFENET@NMFECC.ARPA
Message-Id: <880609083827.20400214@NMFECC.ARPA>
Subject:   Trapping broadcast messages
To:       info-vax@KL.SRI.COM
Comment: From KARNEY@PPC.MFENET on  9-JUN-1988 11:37:05.53 EDT

A month ago, I asked:
        I'm using smg$set_broadcast_trapping and smg$get_broadcast_message to
        trap and redirect broadcast messages.  Two questions about this:

        (1) Is there a way of doing this without involving SMG?  (I'm not
        using SMG otherwise.)

        (2) How you I determine the class of the broadcast message (OPER,
        SHUTDOWN, MAIL, GENERAL, etc.)?  I want to pass this information along
        too.

I received replies from: Jerry Leichter, Mark H. Wood, Kevin Lahey, Tony
Carter, and Eric Loyd.  Thanks for the help!

In brief the answers are (1) Yes, (2) No.

A fuller answer to (1) is:
(a) Associate a mailbox with the terminal with LIB$ASN_WTH_MBX.
(b) Do a IO$_SETMODE on the terminal with TT$M_MBXDSBL, TT$M_NOBRDCST, and
TT2$M_BRDCSTMBX. 
(c) Do a IO$_READVBLK on the mailbox channel specifying a buffer and an AST
completion routine.
(d) The completion routine extracts the broadcast message length from byte
20 and 21 of the buffer, and the message text from bytes 22 on.  It does
whatever it needs to do, and reposts the IO$_READVBLK on the mailbox
channel.

Incidentally, it turns out that I couldn't use SMG$SET_BROADCAST_TRAPPING
to trap the broadcasts because I already had a mailbox associated with the
terminal.

More details are in I/O User's Reference Manual Part I, Sec 8.2.4.

    Charles Karney
    Plasma Physics Laboratory   Phone:   +1 609 243 2607
    Princeton University        MFEnet:  Karney@PPC.MFEnet
    PO Box 451                  ARPAnet: Karney%PPC.MFEnet@NMFECC.ARPA
    Princeton, NJ 08543-0451    Bitnet:  Karney%PPC.MFEnet@ANLVMS.Bitnet

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        KARNEY