Terminal Interruptions
Terminal input/output interruptions are handled by theDMSCIT module.
All interruptions other than those containing device end, channel end,
attention, or unit exception status are ignored. If device end status
is present with attention and awrite CCW was terminated, its buffer is
unstacked. An attention interrupt causes a read to be issued to the
terminal, unless attention exits have been queued via theSTAX macro.
The attention exit with the highest priority is given control at each
attention until the queue is exhausted, then a read is issued. Device
end status indicates that the lastI/O operation has been co.pleted. If
the last1/0 operation was a write, the line is deleted from the output
buffer and the next write, if any, is started. If the lastIIO operation was a normal read, the buffer is put on the finished read list
and the next operation is started. If the read was caused by an
attention interrupt, the line is first checked for the commandsRTI HC, OA, and the appropriate flags are set if one is found. Unit exception indicates a canceled read. The read is reissued, unless it
had been issued withATTREST=NO, in which case unit exception is treated
as device end.
ReaderI Pu nchl Pri nter I nterru ptions
Interruptions from these devices are handled by the routines that
actually issue the correspondingI/O operations. When an interruption
from any of these devices occurs, control passes to Then DMSITI passes control to DMSIOW, which returns contrel to the routine that
issued theI/O operation. This routine can then analyze the cause of
the interruption.User-Controlled Device Interruptions
Interruptsfrom devices under user control are serviced the same as CMS devices except that DMSIOW and DMSITI manipulate a user-created device
table, andDMSITI passes control to any user-written interrupt
processing routine that is specified in the user device table.Otherwise, the processing program regains control directly.
Program Interruptions
The program interruption handler,DMSITP, receives control when a
program interruption occurs.When DMSITP gets control, it stores the
program oldPSi and the contents of the registers 14, 15, 0, 1, and 2
into the program interruption element(PIE). (the routine that handles
theSPIE macro instruction has already placed the address of the program
interruption control area(PICA) into PIE.) DMSITP then determines
whether or not the event that caused the interruption was one of those
selected by aSPIE macro instruction. If it was not, DMSITP passes
control to theDMSABN abend recovery routine.
If the cause of the interruption was one of those selected in aSPIE macro instruction, DMSITP picks up the exit routine address from the
PICA and passes control to the exit routine.Upon return from the exit
routine,DMSITP returns to the interrupted program by loading the
original program check oldPSW. The address field of the PSi was
modified by aSPIE exit routine in the PIE. CMS Introduction 2-9
Terminal input/output interruptions are handled by the
All interruptions other than those containing device end, channel end,
attention, or unit exception status are ignored. If device end status
is present with attention and a
unstacked. An attention interrupt causes a read to be issued to the
terminal, unless attention exits have been queued via the
The attention exit with the highest priority is given control at each
attention until the queue is exhausted, then a read is issued. Device
end status indicates that the last
the last
buffer and the next write, if any, is started. If the last
and the next operation is started. If the read was caused by an
attention interrupt, the line is first checked for the commands
had been issued with
as device end.
Reader
Interruptions from these devices are handled by the routines that
actually issue the corresponding
from any of these devices occurs, control passes to
issued the
the interruption.
Interrupts
table, and
processing routine that is specified in the user device table.
Program Interruptions
The program interruption handler,
program interruption occurs.
program old
into the program interruption element
the
interruption control area
whether or not the event that caused the interruption was one of those
selected by a
control to the
If the cause of the interruption was one of those selected in a
PICA and passes control to the exit routine.
routine,
original program check old
modified by a