Loop
CP Disabled Loop
tern they are using to examine and rearrange files. Refer to the utilities publica
tion for the operating system running in the virtual machine for information on
how to use the utilities.CMS users should use the DASD Dump Restore (DDR) service program to
print or move the data stored on direct access devices. TheVM/SP DASD Dump Restore (DDR) program can be invoked by the CMS DDR command in
a virtual machine controlled byCMS. The DDR program has the following
functions:
DUMP --dumps part, or all, of the data from aDASD device to magnetic
tape.
RESTORE --transfers data from tapes created by DDRDUMP to a direct
access device. The direct access device to which the data is being restored
must be the same type of device as the direct access device originally con
taining that data.
COpy --copies data from one device to another device of the same type.
Data may be reordered by cylinder (or by block number for fixed-blockDASDs) when copied from disk to disk. In order to copy one tape to anoth
er, the original tape must have been created by the DDRDUMP function.
PRINT --selectively prints the hexadecimal and EBCDIC representation ofDASD and tape records on the virtual printer.
TYPE --selectively displays the hexadecimal and EBCDIC representation ofDASD and tape records on the terminal. CMS users should refer to the VM/SP CMS Command and Macro Reference for
instructions on using the DDR command.
The real cause of a loop usually is an instruction that sets or branches on the condi
tion code incorrectly. The existence of a loop can usually be recognized by the
ceasing of productive processing and a continual returning of thePSW instruction
address to the same address. IfI/O operations are involved, and the loop is a very
large one, it may be extremely difficult to define, and may even comprise nested
loops. Probably, the most difficult case of looping to determine is entry to the loop
from a wild branch. The problem in loop analysis is finding either the instruction
that should open the loop or the instruction that passed control to the set of looping
instructions.
The processor operator should perform the following sequence when gathering
information to find the cause of a disabled loop.
1.Use the alter/display console mode to display the real PSW, general registers,
control registers and storage locationsX'OO' - X'lOO'. On an attached processor or multiprocessor system, you must add the prefix
value for thePSA of the other processor (that is, the processor whose console
you are not using) to display, dump, or alter low core storage for the other
processor, or use the M or N operand prefixes described under theDCP, DMCP, and STCP commands.
Introduction to Debugging 483
CP Disabled Loop
tern they are using to examine and rearrange files. Refer to the utilities publica
tion for the operating system running in the virtual machine for information on
how to use the utilities.
print or move the data stored on direct access devices. The
a virtual machine controlled by
functions:
DUMP --dumps part, or all, of the data from a
tape.
RESTORE --transfers data from tapes created by DDR
access device. The direct access device to which the data is being restored
must be the same type of device as the direct access device originally con
taining that data.
COpy --copies data from one device to another device of the same type.
Data may be reordered by cylinder (or by block number for fixed-block
er, the original tape must have been created by the DDR
PRINT --selectively prints the hexadecimal and EBCDIC representation of
TYPE --selectively displays the hexadecimal and EBCDIC representation of
instructions on using the DDR command.
The real cause of a loop usually is an instruction that sets or branches on the condi
tion code incorrectly. The existence of a loop can usually be recognized by the
ceasing of productive processing and a continual returning of the
address to the same address. If
large one, it may be extremely difficult to define, and may even comprise nested
loops. Probably, the most difficult case of looping to determine is entry to the loop
from a wild branch. The problem in loop analysis is finding either the instruction
that should open the loop or the instruction that passed control to the set of looping
instructions.
The processor operator should perform the following sequence when gathering
information to find the cause of a disabled loop.
1.
control registers and storage locations
value for the
you are not using) to display, dump, or alter low core storage for the other
processor, or use the M or N operand prefixes described under the
Introduction to Debugging 483