Method of Operation
This section describes the two major
sections of the D!K!SS prograa. Diagra. 12-1 shows initialization using OSjVS control blocks.
DMKMSS I r
Diagram 12-1
DMKMSS Initialization Diagraa 12-2 shows the processing of a V!/310 request.
Figure 12-1 shows the relationship of
these diagraas. I Diagram 12-2
DMKMSS
Processing
Figure 12-1. Key to the D!KMSS Method of Operation Diagrams
224 IBM VM/310 Service Routines Program Logic

Input DCB CVT I I i
i I UCB I I ECB I Notes Module 1 Use the VS MODESET SVC to get DMKMSS into supervisor state, key O. 1 2 USe the VS OPEN SVC to connect 1 the DCB to the VS control block. If MSS initializes incorrectly, issue
message. If the DCB for the I device does not open, I Issue message. I I 3 Use the STI DP instruction to ensure
running in a virtual machine. If not
running in a virtual machine, issue
message.
4 Follow pointers through the DCB, DEB, and UCB control blocks to
find the channel/unit address assigned
by the VS scheduler. I 5 Set the MSC's attention table index I I in the communication device's I UCB. Also store the address of the I ECB to be waited on in an unused
field of this same communication
Processing Obtain supervisor state, key O.
2 Open the communication DCB.
3 Ensure running in a virtual
machine.
4 Find the communication device I --'------'J'\ v --'------'-1\ v Output DMKMSS ENDING ERROR - MSS NOT INITIALIZED DMKMSS ENDING ERROR - DCB FOR COMM. DEVICE NOT OPENED DMKMSS ENDING ERROR­ DMKMSS MUST RUN IN A VIRTUAL MACH. 1 address. 5 Set up pointers for the attention
interruption.
6 Issue DIAGNOSE code X'7B'
subfunction O. I I 7 Wait for the attention
interruption. Label Ref
RFooo92 1 RFOO1B2
RFOOOB2
RFOO190
L1 I 1 I Notes
6 Build and issue the DIAGNOSE code X'7B' instruction to tell VM/370
the channel/unit address. Issue VS WAIT SVC, specifying that
the event control block will be posted
when the attention interruption is
received. Module Label Ref PROLOG I 1 I I I __ ____ Diagra. 12-1. DftKftSS Initialization Cnapter 12. D!KftSS--The !SS Co •• unicator 225