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

Input Processing Output
1 When the attention interruption is received, issue DIAGNOSE B code X'7B' subfunction X'04'. "- J\. 2 If VM/370 has a request, build INVALID REQUEST CODE IN V SVC 126 parameter list, issue
v
VM REQUEST SVC 126; otherwise, go back
into wait state. 3
Upon return from SVC 126, issue DIAGNOSE code X'7B', subfunction code X'OB' (only
if MSC accepted).
Return to Step 1.
Notes Module Label Ref Notes Module Label Ref
1 This loop will run in the VS DMKMSS MAINLOOP machine as long as MSS support
is in effect. The DIAGNOSE X'7B' instruction points to a
buffer in DMKMSS into which VM/370 places an MSSCOM, or
zeros.
2 Look at MSSCOM to determine L2
volume serial, 3330V device
address, and type of request
(mount or demount). If the RFOO149 request is inval id, issue a
message. If there are no out· standing requests, go into a wait RFOO122 state.
3
The SVC 126 routines issue
orders to the MSC. If the MSC DIAG rejects the order, it sends a unit
check as ending status. SVC then sets a non·zero return code MSSCHECK in register 15. niaaram 12-2. DMKMSS Processing
226 IBM VM/370 Service Routines Program Logic