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
protocol.
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
Module
SEND-------)----------) Sink Virtual Machine External Interrupt--------)
<--------<----------RECEIVE
-----------------)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

THE SEND/RECV PROTOCOL The SEND/RECV protocol defines a transaction calling for two-way
transfer of data, as described in Figure 16. The SEND/RECV protocol
uses the SEND/RECV, RECEIVE, and REPLY subfunctions.
The source virtual machine initiates the transaction using the SEND/RECV using an external interrupt, CP notifies the sink virtual machine that there is a message waiting. The sink virtual
machine uses the RECEIVE subfunction to cause the data to be transfered from the source virtual machine's storage to the sink virtual machine
storage. The sink virtual machine now uses the REPLY subfunction to
cause data to be transferred from its storage to the source virtual
.achine's storage. When the REPLY subfunction completes processing, CP causes an external interrupt in the source virtual machine, notifying it
that the transaction is complete.
The SEND/RECV request requires that ·the source virtual machine
specify the address and length of the data to be transferred and the
address where data is expected from the REPLY subfunction. (Both
addresses are in source virtual machine storage.) These addresses,
along with the length of the data to be transferred, are specified via
the VMCPARM parameter list, described below. When RECEIVE is issued by the sink virtual machine in response to the SEND/RECV request, VMCPARM contains the address in sink virtual machine
storage where data is to be received. Finally, when the REPLY request
is issued, VMCPARM contains the address in the sink virtual machine
storage from which data is to be transferred. r I I DMKVMC I • I VMCF I I Interface I I Module I Source Virtual Machine L-- SEND/RECV-->----------> -----------------)Data I I I (-----------------Data I (--External Interrupt-- I (Final Response) I I Sink Virtual Machine --External Interrupt------) (--------(----------RECEIVE Transfer-------------------) I I (------------(--------REPLY I Transfer-------(------------ I I I I Figure 16. The SEND/RECV Protocol 150 IBM iM/370 System Programmeris Guide