The following procedure should be followed by the processor operator
to record the needed information.
1. Using the alter/display mode of the processcr console, display the
real PSW and CSW. Also, display the general registers and the
control registers.
2. Press the SYSTEM RESTART button in order to get a system abend dump.
3. IPL the system.
Examine this information and attempt to find what caused the wait. If you cannot find the cause, attempt to reconstruct the situation that
existed just before the wait state was entered.
If you determine that CP is in an enabled wait state, but that no IIO interrupts are occurring, there may be an error in the CP routine or CP aay be failing to get an interrupt from a hardware device. Press the SYSTEM RESTART button on the operator's console to cause an abend dump
to he taken. Use the ahend dump to determine the cause of the enabled
(and noninterrupted) wait state. After the dump is taken, IPL the
system. Using the dump, examine the VMBLOK for each user and the real device,
channel, and control unit blocks.. If each user is waiting because of a
request for storage and no more storage is available, there is an error
in CP. There may be looping in a routine that requests storage. Refer to
-Reading CP Abend Dumps" for specific information on how to analyze a CP du.p.
The VM/370 Control Program does not allow the virtual machine to enter a
disabled wait state or certain interrupt loops& Instead, CP notifies
the virtual machine operator of the condition with one of the following
aessages: DMKDSP450W CP ENTERED; DISABLED WAIT PSW DMKDSP451W CP ENTERED; INVALID PSi DMKDSP452W CP ENTERED; EXTERNAL INTERRUPT LOOP DMKPRG453W CP ENTERED; PROGRAM INTERRUPT LOOP and enters the console function .ode. Use the CP commands to display the
following information on the terminal. PSW CSW General registers Control registers
Then use the CP DUMP command to take a dump. Part 1. Debugging with V8/370 29
If you cannot find the cause of the wait or lcop from the information
just gathered, try to reproduce the problem, this time tracing the
processing via the CP TRACE command.
If CMS is running in the virtual machine, the CMS debugging
facilities may also be used to display information, take a dump, or
trace the processing. The CMS SVCTRACE and the CP TRACE commands record
different information. Figure 7 compares the two.
If the virtual machine is in an enabled wait state, try to find out why
no I/O interrupt has occurred to allow processing to resume.
The Control Program treats one case of an enabled wait in a virtual
machine the same as a disabled wait. If the virtual machine does not
have the "real timer" option and loads a PSW enabled only for external
interrupts, CP issues the message DMKDSP450W CP ENTERED; DISABLED WAIT STATE Since the virtual timer is not decreased while the virtual machine is
in a wait state, it cannot cause the external interrupt. A "real timer"
runs in both the problem state and wait state and can cause an external
interrupt which will allow processing to resume. The clock comparator
can also cause an external interrupt.
Three disabled wait conditions can occur during the operation of the RSCS component of VM/370. They can result from either hardware
malfunctions or system generation errors. CP notifies the RSCS operator
of the wait condition by issuing the message DMKDSP450W CP ENTERED; DISABLED WAIT PSW to the RSCS operator's console. Using CP display the virtual machine's PSW. The
characters indicate the error condition.
commands, the operator can
rightmost three hexadecimal !!IT If no RSCS message was issued, a program check
interrupt occurred during the execution of the program check handler. A
programming error is the probable cause.
If the RSCS message DMTREX091T INITIALIZATION FAILURE -- RSCS SHUTDOWN was issued, RSCS operation has been terminated due to an error in the
loading of DMTAXS or DMTLAX. A dump of virtual storage is automatically
taken. Verify that the CMS files DMTAXS TEXT and DMTLAX TEXT are
correctly written and resident on the RSCS system-residence device. 30 IBM System Programmer's Guide
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