Appendix A: VM/370 Extended Control-Program Support
VM/370 Extended Control-Program SUppOit (ECPS) VM/370 Extended Control-Program Support hardware-assisted parts: (ECPS) consists of three
1. Control program assist (CP assist) defines new hardware
instructions to assist CP routines and functions or, in two cases,
as new interpretations of existing VM/370 instructions. CP assist
does not operate in a VM/370 system that runs under VM/370. 2. Expanded virtual machine assist
existing virtual machine assist.
provides an expansion of the
3. Virtual interval timer assist provides a more accurate hardware
updating of the interval timer for the virtual machine. See snQ for a list of the
processors on which Reps is ECPS INTERACTION WITH OTHER FUNCTIONS • Virtual machine assist -The expanded virtual machine assist can be enabled only if virtual machine assist is also enabled. • Program event recording -No PER events are recognized by CP assist. Virtual machine assist does recognize PER events for certain
instructions. PER events are not recognized during the updating of
the virtual interval timer. • VS1 assist
other. VM/370 ECPS and VS1 assist do not interfere with each • DOS emulator -If the DOS emulator is active, virtual machine assist
is disabled. CP assist and the virtual interval timer assist are not
disabled if the DOS emulator is active. CONTROL BY CONTROL REGISTER 6 AND MICBLOK ASSIST CONTROL FIELD
The contents of control register 6 exercise overall and absolute control
over virtual machine assist, CP assist, expanded virtual machine assist,
and virtual interval timer assist. Values in control register 6 share
control of functions provided by expanded virtual machine assist with
the setting of bits in the MICBLOK's assist control field. The use of
the assist control field is described later on under the topic "Expanded Virtual Machine Assist."
The following table defines the contents of control register 6: o Virtual machine assist enabled if on, disabled if off
1 Virtual machine in problem state if on, in supervisor state if
off
Appendix A: VM/370 Extended Control-Program Support 1-409

2 ISK and SSK instructions not allowed if on, allowed if off
3 System/360 instructions only if on, System/370 instructions if
off
4 Virtual SVC interrupts not allowed if on, allowed if off
5 Shadow table fixup allowed if on, not allowed if off
6 Control program assist enabled if on, disabled if off
7 Virtual interval timer support enabled if on, disabled if off
8-28 Real address of virtual machine pointer list
29-31 Unused, must be zero
The following chart summarizes the control by control register 6 of
virtual machine assist, extended virtual machine assist, CP assist, and
the virtual interval timer assist: • virtual Control
Machine Program
Assist Assist
Bit 0 Bit 6
o
o
o
o
1
1
1
1
o
o
1
1
o
o
1
1
virtual
Interval
Timer
Assist
Bit 7
o
1
o
1
o
1
o
1
Enabled
Assists
None
None CP assist CP assist Virtual machine assist Virtual machine assist,
virtual interval tiller
assist Virtual machine assist, CP assist, expanded
virtual machine assist Virtual machine assist, CP assist, expanded
virtual machine assist,
virtual interval timer
assist I * Not possible with VM/370 I A indicates SET SASSIST ON I B indicates SET SASSIST OFF I C indicates SET CPASSIST ON I D indicates SET CPASSIST OFF Systelll Opera tor
Comlland
B, D
*
B, C
*
A, D
A, D
A, C
A, C I E indicates SET ASSIST ON with TMR or NOTMR as indicated User COllmand E, NOTMR E, TMR E, NOTMR E, TMR __________ . ____________ . ________ .-- __________________ .-- _________________________ -J 1-410 IBM VM/370 System Logic and Problem Determination--Volume 1