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

VIRTUAL 8ACHINE POINTER LIST The virtual machine pointer list (8ICBLOK) is a 24-byte area that starts
on a doubleword boundary and contains eight fullwords. Control register
6 contains an address that points to the beginning of the virtual
aachine pointer list. address is formed by concatenating bits 8 through 28 of control register 6 with three low-order zero bits. All
storage accesses to the virtual machine pointer list are done with real
addresses and with a storage protect key of O. The following table defines the full words at the specified offsets
into the virtual machine pointer list. The usage of the workspace
pointer and the workspace itself is implementation-dependent. The usage
of the pointer and the workspace is not further defined in this
document. +0 Real segment table pointer +4 Virtual control register pointer +8 Virtual PSW pointer
+12 Workspace pointer
+16 Virtual interval timer pointer +20 Assist control field
+24 Reserved for IB8 use
TRACE TABLE ENTRIES The first bit of each V8/310 trace table entry generated by ECPS is set
to one (1). Information about V8/310 trace table entries is contained
in the !B8 RELATIONSHIPS BETWEEN HARDWARE ASSISTS Figure 27 illustrates the possible ways of running a virtual machine with various combinations of hardware assists and how the SET command
affects their operation.
Appendix A: VM/370 Extended Control-Program Support 1-411