A force start is required when checkpoint start encounters I/O errors
while reading files, or invalid data. The procedure is the saae as for
checkpoint start except that unreadable or invalid files are bypassed.
CP COMMANDS The CP commands allow you to control the virtual machine froa the
terainal, much as an operator controls a real aachine. Virtual machine
execution can be stopped at any time by use of tbe terminal
1
s attention key (for 3066 and 3270 terminals, the ENTER key is used); it can be
restarted by entering the appropriate CP command. External, attention,
and device ready interrupts can be siaulated on the virtual aachine.
Virtual storage and virtual machine registers can be inspected and
.odified, as can status words such as the PSi and the CSi. Extensive
trace facilities are provided for the virtual machine, as well as a
single-instruction mode. Commands are available to invoke the spooling
and disk sharing functions of CP.
CP com.ands are classified by privilege classes. The VM/370 directory entry for each user assigns one or more privilege classes.
The classes are primary systea operator (class A), system resource
operator (class B), system progra.aer (class C), spooling operator
(class D), system analyst (class E), service representative (class P), and general user (class G). Commands in the system analyst class may be
used to inspect real storage locations, but may not be used to make aodifications to real storage. Co.mands in the operator class provide
real resource control capabilities. System operator commands include
all coamands related to virtual aachine performance options, such as
assigning a set of reserved page frames to a selected virtual aachine. Par descriptions of all the CP commands, see the 1M/370 fo!: General and the V!!/370 CP Introduction 1-9
Program States When instructions in the Control Progra. are being executed, the real
coaputer is in the supervisor state; at all other ti.es, vhen running
virtual machines, the real co.puter is in the proble. state. Therefore, privileged instructions cannot be executed by the virtual .achine.
programs running on a virtual machine can issue privileged instructions;
but such an instruction either (1) causes an interruption that is
handled by the Control program, or (2) is intercepted and handled by the
processor, if the virtual .achine assist feature or V8/310 Extended Control-program Support is enabled and supports that instruction. CP examines the operating status of the virtual machine PSW. If the
virtual machine indicates that it is functioning in supervisor mode, the
privileged instruction is simulated according to its type. If the
virtual machine is in problem mode, the privileged interrupt is
reflected to the virtual machine. Only the Control Program .ay operate in the supervisor state on the
real machine. 111 programs other than CP operate in the proble. state
on the real .achine. 111 user interrupts, including those caused by atte.pted privileged operations, are handled by either the control program or the processor (if the virtual .achine assist feature or VM/310 Extended Control-Program Support is available). Only those
interrupts that the user progra. vould expect fro. a real machine are
reflected to it. 1 problem progra. viII execute on the virtual .achine
in a .anner identical to its execution on a real Syste./310 processor,
as long as it does not violate the CP restrictions. See V8/310 Syste. for a list of the restrictions. 1-10 IB! VM/370 System Logic and Problem Deteraination--Volu.e 1
Previous Page Next Page