Type ASSEMBLE
Source Lines : 524
Fixes Applied : 1
Most Recent Version : Thursday, December 7, 1978
Last Fix ID : [R10283DT]

Module

       DMTIOM

Function

        THE  DMTIOM  MODULE  CONTAINS BOTH  THE  MSUP  I/O
        INTERRUPT  HANDLER   AND  THE  TASK   I/O  SERVICE
        ROUTINE. THE I/O SERVICE PROVIDED BY DMTIOM TO THE
        TASK  PROGRAMS   INCLUDES  SEQUENTIAL   SUBCHANNEL
        SCHEDULING, CHANNEL  PROGRAM EXECUTION,  AUTOMATIC
        SENSE  EXECUTION  ON UNIT  CHECK  WHEN  REQUESTED,
        RETURN OF ALL PERTINENT  INFORMATION REGARDING THE
        EXECUTION OF THE CHANNEL PROGRAM, AND NOTIFICATION
        VIA  POST   ON  COMPLETION   OF  CHANNEL   PROGRAM
        EXECUTION.

Attributes

       REUSABLE

       INTERRUPT ENTRY EXECUTABLE DISABLED ONLY

Operation

        THE I/O  SERVICE ROUTINE IS  ENTERED VIA  A BRANCH
        AND  LINK FROM  TASK  PROGRAMS.  EXECUTION OF  THE
        CALLING TASK IS IMMEDIATELY  SUSPENDED BY MEANS OF
        THE  FREEZE SVC.  A  SUPERVISOR  QUEUE ELEMENT  IS
        GOTTEN  BY  MEANS OF  A  CALL  TO DMTQRQ,  AND THE
        APPROPRIATE  I/O   ELEMENT  IS  BUILT   USING  THE
        INFORMATION  SPECIFIED IN  THE  I/O REQUEST  TABLE
        SUPPLIED BY THE CALLER.  THE APPROPRIATE (SELECTOR
        OR MULTIPLEXOR) CHANNEL QUEUE IS SCANNED TO LOCATE
        THE POSITION OF THE SUBQUEUE FOR THE SUBCHANNEL ON
        WHICH THE  I/O IS  TO BE  EXECUTED. IF  A SUBQUEUE
        ALREADY EXISTS FOR THE SUBCHANNEL, THE IMPLICATION
        IS THAT  THE SUBCHANNEL IS  BUSY WITH  ANOTHER I/O
        REQUEST EXECUTION.  IN THIS CASE, THE  NEW REQUEST
        ELEMENT IS ENQUEUED AT THE END OF THE SUBQUEUE FOR
        LATER  EXECUTION, AND  CONTROL  IS  PASSED TO  THE
        DISPATCHER. IF NO SUBQUEUE EXISTS, THE NEW ELEMENT
        BECOMES  THE  FIRST  ENTRY  IN  THE  SUBQUEUE  AND
        CONTROL IS PASSED TO THE  ROUTINE WHICH STARTS I/O
        REQUEST ELEMENTS.

        ON ENTRY FROM AN I/O INTERRUPT, DMTIOMIN SAVES THE
        EXECUTION  STATUS IF  NECESSARY  AND SEARCHES  THE
        APPROPRIATE  I/O  QUEUE  TO  FIND  AN  ACTIVE  I/O
        REQUEST ELEMENT ON THE  INTERRUPTING DEVICE. IF NO
        SUCH ELEMENT  IS FOUND, THE ASYNCHRONOUS  I/O EXIT
        QUEUE IS  SCANNED FOR  A MATCHING  DEVICE ADDRESS,
        AND AN  ASYNCHRONOUS EXIT IS  TAKEN IF A  MATCH IS
        FOUND. IF  NEITHER AN  ACTIVE I/O  REQUEST ELEMENT
        NOR  AN  ASYNCHRONOUS  EXIT   REQUEST  ELEMENT  IS
        LOCATED FOR THE INTERRUPTING DEVICE, THE INTERRUPT
        IS   IGNORED  AND   CONTROL  IS   PASSED  TO   THE
        DISPATCHER.

        IF AN ACTIVE I/O ELEMENT IS FOUND, THE ELEMENT AND
        THE ASSOCIATED  I/O REQUEST TABLE IN  TASK STORAGE
        ARE UPDATED TO  REFLECT THE NEW STATUS  OF THE I/O
        REQUEST  EXECUTION. IF  THE INTERRUPT  IS A  STAND
        ALONE PCI, THE ASYNCHRONOUS  EXIT REQUEST QUEUE IS
        SCANNED  FOR A  MATCHING DEVICE  ADDRESS, AND  THE
        EXIT IS TAKEN IF ONE  IS FOUND. THE UPDATED ACTIVE
        I/O  REQUEST TABLE  IS  INSPECTED  TO SEE  IF  THE
        REQUESTED I/O PROCESSING HAS  COMPLETED. IF IT HAS
        NOT,  CONTROL  IS  IMMEDIATELY   RETURNED  TO  THE
        DISPATCHER. OTHERWISE,  THE I/O  REQUEST TABLE  IS
        INSPECTED TO  SEE IF UNIT  CHECK HAS BEEN  SET AND
        AUTOMATIC SENSE HAS BEEN REQUESTED. IF THIS IS THE
        CASE, ANOTHER  SUPERVISOR QUEUE ELEMENT  IS GOTTEN
        BY MEANS  OF A CALL  TO DMTQRQ, THE  SENSE CHANNEL
        PROGRAM  IS BUILT  IN  THE  NEW ELEMENT,  THE  NEW
        ELEMENT IS CHAINED TO THE REQUEST ELEMENT, AND THE
        SENSE OPERATION IS STARTED. IF THE SENSE OPERATION
        DOES NOT  IMMEDIATELY COMPLETE, CONTROL  IS PASSED
        TO THE DISPATCHER.

        WHEN SERVICE FOR A REQUEST IS COMPLETELY FINISHED,
        THE ASSOCIATED I/O ELEMENT  (AND SENSE ELEMENT, IF
        PRESENT) ARE DEQUEUED AND FREED BY MEANS OF A CALL
        TO DMTQRQ,  AND THE REQUESTING TASK'S  I/O REQUEST
        TABLE IS POSTED BY MEANS OF  A CALL TO DMTPST.  IF
        ANOTHER  I/O REQUEST  ELEMENT  IS  PENDING ON  THE
        SUBQUEUE  FOR   THE  SUBCHANNEL  WHICH   HAS  JUST
        COMPLETED THE PREVIOUS  REQUEST EXECUTION, CONTROL
        IS PASSED TO THE ROUTINE  WHICH STARTS I/O REQUEST
        ELEMENTS.  OTHERWISE,  CONTROL IS  PASSED  TO  THE
        DISPATCHER.

        THE ROUTINE WHICH STARTS  I/O REQUEST ELEMENTS MAY
        BE ENTERED EITHER FROM I/O INTERRUPT PROCESSING OR
        I/O  REQUEST SERVICE.  ITS FUNCTION  IS SIMPLY  TO
        MOVE THE STARTING CCW ADDRESS  FROM THE TASK'S I/O
        REQUEST TABLE  TO THE LOW  STORAGE CAW,  AND START
        THE I/O CHANNEL PROGRAM ON THE APPROPRIATE DEVICE.
        IF  THE  I/O  COMPLETES  IMMEDIATELY,  CONTROL  IS
        PASSED DIRECTLY TO THE ROUTINE WHICH COMPLETES I/O
        REQUEST PROCESSING  AND SELECTS  A NEW  REQUEST ON
        THE  SUBCHANNEL  FOR  PROCESSING.   IF  A  PENDING
        ASYNCHRONOUS INTERRUPT  FOR THE DEVICE  IS CLEARED
        BY  THE SIO,  THE ROUTINE  SETS  A REGISTER  WHICH
        CAUSES THE INTERRUPT  TO BE FAKED PRIOR  TO RETURN
        TO THE DISPATCHER.

Calls to Other Routines

       DMTQRQ -   TO RESERVE OR RELEASE SUPERVISOR QUEUE ELEMENTS
       DMTDSP -   TO RESUME DISPATCHED PROCESSING