IBM Professional Series User Manual page 169

meaning but the data that they point to should not be
destroyed by this user exit routine (for example, register 13
save area).
The HST ACC routine must not issue commands that will
allow the system to interrupt the VMPCSERV processing
(such as "CP SET MSG ON"). The HOST and the VM/PC
Local processors are paced and required to answer each
other in a timely sequence. If this sequence is interrupted,
the connection will be broken and VMPCSERV will stop.
It
will be necessary to IPL the HOST CMS to recover the
machine.
Remember if you use any spooling type functions in this exit,
the local VM/PC user may also be using them. This could
be confusing unless you save and restore the current values
that the local processor set, prior to exiting from HSTACC
each time. Spooling messages are impossible to stop and
may interrupt VMPCSERV. Unless the screen is reset in the
host machine on time, VMPCSERV may terminate.
Because VMPCSERV preserves the users environment and
restores it at the completion of the service process, there are
no disks accessed other than the system
"s"
disk. This is so
that the local VM/PC can use all 25 mode letters other than
S. It is not recommended that any file I/O be performed in
this EXIT. piagnose "4C" should be used to create
accounting data, but it is also possible to accumulate the
transactions in buffers, and then send them to the accounting
or other machine to be processed. See the description of the
second entry point, above, for more information.
HSTACC should only be used to accumulate or interrogate
the names of the files that are being requested by the
LOCAL processor (VM/PC). The exit will be given control
with register one (R1) pointing to the filename, filetype, and
filemode. HSTACC could accumulate or filter the names of
the downloaded files and send formatted accounting records
of them to an accounting machine or use the DIAG X'4C'
directly. The Accounting machine could then reduce the
data and create a list of programs that are being used by the
local VM/PC.
6-20
VM/PC Users
Guide