Pseudo Timer
Pseudo Timer Start I/O
Pseudo Timer DIAGNOSE
The pseudo timer is a special VM/SP timing facility. It provides 24 or 32 bytes of
time and date information in the format shown in Figure 28.
Start I/O Diagnose
<------ 8 bytes -------> <--- 8 bytes > HH:MM:SS HH:MM:SS
or VIRTCPU I TOTCPU VIRTCPU TOTCPU Figure 28. Fonnats of Pseudo Timer Infonnation
The first eight-byte field is the date, in EBCDIC, in the form
Month/Day-of-Month/Year. The next eight-byte field is the Time of Day in
Hours:Minutes:Seconds. The VIRTCPU and TOTCPU fields contain virtual
processor and total processor time used. The units in which the processor times are
expressed and the length of the fields depend upon which of two methods is used
for interrogating the pseudo timer.
The pseudo timer can be interrogated by issuing a START I/O to the pseudo timer
device, which is device type TIMER, and is usually at device address OFF. No I/O interrupt is returned from the SIO. The address in virtual storage where the timer
information is to be placed is specified in the data address portion of the CCW
associated with the SIO. This address must not cross a page boundary in the user's
address space. If this method is used, the virtual processor and the total processor
times are expressed as full words in high resolution interval timer units. One unit is
13 microseconds.
The pseudo timer can also be interrogated by issuing DIAGNOSE with an opera­
tion code of C, as described under "DIAGNOSE Instruction in a Virtual Machine." If this method is used, the virtual and total processor times are expressed as
doublewords in microseconds.
Timers in a Virtual Machine 207

CP in Attached Processor and Multiprocessor Modes
Multiprocessor Environment
This chapter enables you to: • Define attached processor (AP) mode
Define multiprocessor (MP) mode • Understand the use of the channel set switching instructions when available • Understand the use of the privileged instructions that set and inspect the
processor's prefix register
Understand the use of the privileged instruction that determines the address of
the processor that is executing
Understand the use of hardware signaling to communicate between processors • Understand the use of a TOD clock synchronization check
Code fetch and store sequences that can be safely used in the AP /MP envi­
ronment • Use locks for serialization of functions
Set processor affinity
Change processors using the SWTCHVM macro
Configure I/O devices to obtain maximum availability and recovery potential
Debug an AP/MP system.
In a tightly coupled multiprocessor (MP) environment two processors share real
storage under the control of a single control program. Both processors have I/O capability in an MP environment. See the section "Configuring I/O Devices" for a
discussion on how to configure I/O devices for maximum availability and recovery
potential.
In a dyadic environment two processors share real storage under the control of a
single control program. Both processors have I/O capability. However, unlike an MP complex, a dyadic processor cannot be partitioned into two distinct
uniprocessor systems.
Attached Processor Environment
In an attached processor (AP) environment two processors share real storage under
the control of a single control program. However, unlike a multiprocessing envi­
ronment, only one processor in an AP environment has I/O capability. If you are
running on a 3033 or a 3081, the channel set switching feature is available. If a
severe hardware error occurs on the first processor in an AP environment, the con­
trol program may be able to use the channel set switching feature to dynamically 208 VM/SP System Programmer's Guide