April 1, 1981
GENERAL CONSIDERATIONS The SENDX function is a fast way to transfer messages or data and can be
used in place of the CP MSG command where the message length exceeds the
capacity of the terminal input line. Its use is somewhat restricted in
that the maximum data length must be agreed upon by all VMCF users and
then remains fixed unless reneqotiated.
The SEND and SEND/RECV functions are better suited to transfer high
volume data base type information. This type of data transfer requires
the flexibility of a wide range of data lengths along with rigorous
management and control techniques.
The QUIESCE function allows a virtual machine to discontinue
receiving messages. The virtual machine can process those messages
already stacked and then use the RESUME function to continue reception.
The QUIESCE function also allows a virtual machine to process all queued
messages prior to terminating VMCF operation.
The user parameter list, VMCPARM, is designed such that it can be
used foc any subfunction by simply varying the contents of its fields. Users should keep copies of VMCPARMs for all requests made via the SEND, SEND/RECV, or SENDX functions. When a final response interrupt is
received and the interrupt message header indicates no data transfer
errors, the corresponding VMCPARM copy can be released. If a data tcansfec error is indicated, the copy can be used to reinitiate the
tr ansact ion.
VMCF Protocol VMCF pcovides four types of protocol: SEND, SEND/RECV, SENDX, and IDENTIFY. The protocol used to communicate between two virtual machines
depends on the application of VMCF and conventions established by
virtual machine users authorized to use VMCF. A virtual machine must
in voke the AUTHORIZE subfunct ion before it is allowed to use any of the
other subfunctions.
The types of transactions that virtual machines can be involved in
are described by a series of VMCF protocols. In these protocols the
originating virtual machine is called the "source" virtual machine. The
dest inat ion virtu al machine is called the "sink" virt ual machine.
The pcotocol for a transaction remains in effect for the duration of
the transaction.
THE SEND PROTOCOL The SEND pcotocol defines a one-way transfer of data from source virtual
machine stocage to sink virtual machine storage. The SEND protocol uses
the SEND and RECEIVE subfunctions, as described in Figure 15. The source victual machine first transfers data to the sink virtual machine.
This is done by executing the SEND subfunction which specifies the
userid of the sink virtual machine, a message ID, and the address and
length of the data being sent. The sink virtual machine receives an
external interrupt from CP notifying it of the data transfer request.
The sink virtual machine can then respond via the RECEIVE subfunction.
The RECEIVE request specifies the address and the length of the SINK buffer that is to receive the data and causes the data to be transferred
148 IBM VM/370 System Programmer's Guide
from source virtual machine storage to sink virtual machine storage. When the data transfer is complete, the source virtual machine receives
__ L ____ ' !_L _____ L &___ __ L! __ L ______ L! __ au LLVW 1S complete and that the sink virtual machine has received the data.
All virtual machines authorized to use VMCF can send data using this
The amount of data
storage size. Data
necessary) and only
transfer operation.
transferred is limited only by virtual machine
is transferred in blocks of up to 2K (when
one real page frame is locked during the data Source Virtual Machine DMKVMC VMCF Interface
SEND-------)----------) Sink Virtual Machine External Interrupt--------)
-----------------)Data Transfer---------------------) I I <--External Interrupt--I I (Final Response) I I I I I I I I Figure 15. The SEND Protocol Part 2. Centrol program (CP) 149
Previous Page Next Page