A flexible approach is loading an operating system via the 1PL command. you have a choice. You can 1Pt by device address or by
system nane. If you IPt by the virtual address of the device containing
the operatinq system, you can also clear virtual storage to binary zeros before loajing the system:
ipl 190 ::lear This can be useful if your operating system does not
automatically clear storage when it is loaded. You can stop the IPt procedure at a point just before the initial PSi is loaled by issuing the IPt command with the STOP operand:
ipl 190 stop
At this point, you can issue CP commands to display or alter data in your - I. _, _ I""" 11:..a.\".,..L:: u::::> • beqin ..:I. ,",VIUWa.U u. You can loa5 your operating system by name provided that the name
refers to a system that has been previously saved by your installation's
system programmer. As an example:
ipl 10svs If do load by name, the options to clear storage or to stop before lOlling the initial PSW are not availablee Whether you TO! by device address or by name, you can pass up to 64 bytes lata (including embedded and trailing blanks) to your operating
system the IPt command. The data is entered following the keyword PARM: io1 10svs parm this data will be passed VM/370 loajs the qeneral registers, starting with register zero with
the contents of the command line beginning with the first nonblank
character after the keyword PARM and ending with the last character or
blank Embedded and trailing blanks are passed. For the previous example, the qeneral reqisters contain the followinq: G?R 0 THIS OAT A WI LL B GPR 4 E PA SSEO xxxx xxxx GPR 8 xxxx xxxx xxxx xxxx G1?R 12 xxxx xxxx xxxx xxxx
where x x ••• lenotes no change to previous contents.
If VOU hld entered three blank characters following the word "passed"
in the command line, the registers would contain: r;PR 0 GPR 4 GOR 8 G1?R 12 TQIS E PA xxxx
xxxx
OAT SSEO xxxx
xxxx
A WI x
xxxx
xxxx
Lt B
xxxx
xxxx
xxxx
For further information on the PARM operand, refer to the "Usage Notes"
discussion of the IPL command in Section 5.
Section 3. CP Command Usage 23

SIMULATIN3 INTERRUPTS The EXTERNAL command can be used to simulate an external interruption to
the virtual machine and return control to that virtual machine. If you
enter the command: external a default interrupt code of X'40' is assumed. This code corresponds to
pressing the external interrupt key the real system control panel. You can also specify an interruption code within the range of X'01' throuqh X'FF':
external A8
If your virtual machine has the ECMODE option specified in the VM/370 directory, you can also code X'1004' (clock comparator interruption) and X'1005' (:PU timer interruption). The interruption code that you enter
or default to, is placed in position 16 through 31 of the PSi if you are
operatinq in basic control (BC) mode. If your machine is in extended
control (Ee) mode, the interruption code is placed in the two bytes at
location X'84'. An external interruption is then presented to your
virtual machine and subsequent action is determined by your operating
system. If vour virtual machine is operating in the basic control mode (ECMODE OFF), virtual addresses specified can be no higher than 5FF
(channels 0 through 5). If it is operating in extended control mode (ECMODE ON), all addresses through FFF are valid.
The attention or request keys on the real console can be simulated by
the CP commands:
attn
-- or --
request
In either case, the effect is to interrupt the runninq condition of the
virtual machine and ready it for console input.
ENTERING CP COMMANDS There are several ways that you can interrupt the running of your
virtual machine in order to execute CP commands. You can stop the
virtual machine and place it in a virtual console read environmenti you
can go from a virtual console read environment to the CP environmenti
and, you stop a virtual machine and place it directly into the CP environment.
ENTERING CP COMMANDS WHEN THE VIRTUAL MACHINE IS RUNNING If your terminal mode is set to VM, pressing the attention key (or its
equivalent) once stops the virtual machine and places it into the
virtual console read environment. You can now execute CP commands by
24 IBM CP Command Reference for General Users