If the receiving virtual machine chooses not to accept special messages at any time, it can merely issue SET S8SG OFF. CP would then inform any machine issuing the SMSG command that the virtual machine is
not receiving special messages. When it is ready to resume accepting
special messages, the machine need only to issue SET S8SG ON. The following shows the processing when an SMSG command is issued.
r 1 S8SG userid msgtxt
, 1 CP: 1 • Validates S8SG command. 1 • Checks that receiving virtual machine 1 has Special Message flag ON (in receiving 1 If not --1----------, • Checks for receiving virtual machine being 1 1 authorized with CP. If not--- --------->1 • Obtains storage for containing one VMCF I ,---------- External Interrupt Buffer. ISend message to • Builds VMCF parmeter list: lissuer that I - saves buffer address in VKVMVADA Ireceiving machine I - computes message length & stores that lis not receiving I length in VKVMLENA Ispecia1 messages I - mOves message test into area pointed to ' I ' BY VMCMBUF (VMCMVADA value minus 40 1 bytes) for the computed length of the , message text EIIT
- stores SENDI subfunction code in VMCMFUNC - stores CPU clock value in VMCMMID as a
unique message-id • Calls DMKVMC to execute SEND I subfunction
code to send the message to the receiving
virtual machine. I , , Receiving virtual machine processes datal
fro. buffer transmitted via SENDI. I During a Special Message session, the following error messages could be
sent back to the issuer of the SMSG command: DMKMSG003E: DMKKSG020E: DKKKSG04SW: DMKMSGOS7E: INVALID OPTION - option USERID MISSING OR INVALID userid NOT LOGGED ON userid NOT RECEIVINGi [DISCONNECTED I MSG OFF I SMSG OFF I NOT AUTHORIZED I WNG OFF] 1-42 IBM V8/370 System Logic and Problem Determination--Vo1ume 1

VM/VS Handshaking
The V8/VS Handshaking feature provides a communication path between CP and virtual machine operating systems that makes each system control
program aware of certain capabilities or requirements of the other.
The following is a discussion of VM/VS Handshaking as it relates to OS/VS1. Functions of VM/VS Handshaking incorporated in the V8/370 control program are available and applicable to any operating system that can be system generated to use this V8/370 enhancement. VM/VS Handshaking for OS/VSl performs the following functions: • Closes CP spool files when the VS1 job output from its DSO, terminator, and output writer is complete • Processes VSl pseudo page faults • Provides an optional nonpaging mode for VS1 when it is run in the VK/310 environment
When a VS1 virtual machine with the handshaking feature is loaded
(via IPL), its initialization routines determine whether the handshaking
feature should be enabled. First, VS1 determines if it is running under
the control of V8/370 by issuing a STIDP (Store Processor ID)
instruction. STIDP returns a version code; a version code of X'FF' indicates VS1 is running with VM/310. If VS1 finds a version code of X'FF', it then issues a DIAGNOSE (X'OO') instruction to store the V8/370 extended-identification code. If an extended-identification code is
returned to VS1, VS1 knows that VM/370 supports handshaking; if nothing
is returned to VS1, V8/370 does not support handshaking. At this time
or any time after IPL, the operator of the VS1 virtual machine can issue
the CP SET PAGEX ON command to enable the pseudo page fault handling
portion of handshaking. If the VS1 virtual machine is in the nonpaging mode and, if the pseudo page fault handling is active, full handshaking
support is available.
Because the VS1 system does no paging, any ISAM programs run under VS1 are treated by V8/310 as though they are running in an ADDRSPC=REAL partition. the IS!8 option is required for the VS1 .achine
to successfully execute the 151M program.
If the handshaking feature is active, VS1 closes the CP spool files when
its job output fro. the DSO, terminator, and output writer is complete. Once the spool files are closed, V8/370 processes thea and they are sent
to the real printer or punch. During its job termination processing, VSl issues a DIIGNOSE (1
1
08') instruction to pass the CP CLOSE command
to V8/370 for each CP spool file. A page fault is program interruption that occurs when a page aarked "not in storage" J.S referred to by an instruction with an active page.
The virtual machine referring to the page is placed in a wait state
while the page is brought into real storage. Without the handshaking
feature, the entire VS1 virtual machine is placed in page wait by V8/370 until the needed page is available. CP Introduction 1-43