🚀 go-pugleaf

 On Mon, 27 Jul 1992, portal!cup.portal.com!TRADER@UUNET.UU.NET said:
>I'm familiar with using EXCP to do channel I/O. However the IOB
>structure and EXCP seem to be geared towards devices that do not present
>asynchronous attention interrupts. In VM environments, it is very easy
>to setup interrupt handlers with HNDIO.
>How does one write code in MVS to handle devices such as 3270 terminals
>that present asynchronous interrupts?

    I fought this war before.  Why can't IBM document how to write
 an I/O Attention routine for MVS.

    Three suggestions:

    Look at CBT tape file 353 from Brian Cook of Morton Thiokol.
 His ETPS program uses an I/O Attention that can talk to local
 non-SNA 3270 terminals before VTAM, JES2 or other sub-systems
 are even started.  His code has broken and been fixed when we
 switched operating systems but it is at least a good sample.
 He at one time even had a one byte overlay of SQA.  He moved
 his program plus one byte to SQA in space only large enough
 for his program. Meaning: Test off hours.
 If you need my copy that runs in MVS/SP 2.2.3, just ask.

    Look at IBM's I/O Attention routines.  I believe that the
 free BTAM one was called IECTATEN or something like it.
 VTAM and JES2 should have I/O Attention routines also.

    The last suggestion is to give up and use VTAM, TCAM, or
 BTAM to talk to 3270 terminals.

    Note: If you can ever get good documentation for IBM, please
 send me a copy.