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