CP Enabled Wait
Virtual Machine Disabled Wait
Virtual Machine Enabled Wait
If you determine that CP is in an enabled wait state, but that no I/O interrupts are
occurring, there may be an error in the CP routine or CP may be failing to get an
interrupt from a hardware device. Force a CP system restart at the operator's con­
sole to cause an abend dump to be taken. Use the abend 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 dump.
The VM/SP Control Program does not allow the virtual machine to enter a disa­
bled wait state or certain interrupt loops. Instead, CP notifies the virtual machine
operator of the condition with one of the following messages: DMKDSP450W CP ENTERED; DISABLED WAIT PSW DMKDSP451W CP ENTERED; INVALID PSW DMKDSP452W CP ENTERED; EXTERNAL INTERRUPT LOOP DMKPRG453W CP ENTERED; PROGRAM INTERRUPT LOOP and enters the console function mode. Use the CP commands to display the fol­
lowing information on the terminal.
PSW
CSW
General registers
Control registers
Then use the CP DUMP or VMDUMP command to take a dump.
If you cannot find the cause of the wait or loop from the information just gathered,
try to reproduce the problem, this time tracing the processing via the CP TRACE
or CP PER commands.
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, CP TRACE, and CP PER commands record different information.
Figure 66 compares the CP and CMS facilities for debugging.
If the virtual machine is in an enabled wait state, try to find out why no I/O or
external interrupts have 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, CP issues the message DMKDSP450W CP ENTERED; DISABLED WAIT STATE Introduction to Debugging 487

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 allows processing to
resume. The clock comparator can also cause an external interrupt.
Summary of VM/SP Debugging Tools
Figure 65 summarizes the VM/SP commands that are useful for debugging pro­
grams in a virtual machine. The CP and CMS commands are classified by the func­
tion they perform.
488 VM/SP System Programmer's Guide