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

operator loads V8/370 r--t 11--------1 1 I II L
Hardware assist status:
CP assist on,
virtual machine assist
on,
expanded virtual machine
assist on.
virtual interval timer
assist on II Class 1 (operator) com­ mands possible before a
virtual machine user is
dispatched. II r --, I These hardware assists are on I after VM/370 is loaded on the I following .achines: Systea/370 Models I 1 35-3 , 1 38 , 14 5-3 , an d 1 4 8 L--- r___ I SET CP1SSIST OFF I SET CP1SSIST ON I SET SlSSIST OFF I SET SlSSIST ON L--- I Operator issues hardware I----------------r----------------------, I assist commands I If no operator hardware
assist commands are
issued, go to part 4 (F) II ..----, I F I L---.J Part 4 Operator issues SET CPASSIST OFF Results:
1
CP assist is eff, I expanded virtual I machine assist is I off, I virtual machine I assist is on I If no more oper­
ator hardware as­
sist com.ands are
issued, go to
part 2 (B) Operator issues SET CPASSIST OR , ,.--I-, I A I L---.I Part 1 Operator issues SET SASSIST OFF r , Results:
CP assist is on,
expanded virtual machine assist is
off,
virtual machine assist is off
virt. intv. timer assist is off
If no more oper­
ator hardware as­
sist commands are
issued, go to
part 3 (D) Operator issues SET SASSIST ON , ,.--I-, I A I L---.I Part 1
Figure 27. Hardware Assist Relationships (Part 1 of 4)
1-412 IBft Vft/370 System Logic and Problem Determination--Volume 1