3850 MSS To specify alternate channel addresses on the RCTLUNIT macro, code: RCTLUNIT ADDRESS=cuu,CUTYPE=nnnn,FEATURE=xxx-DEVICE, ALTCH= (1,2,4)
Figure 13 shows how the real I/O control block structure would be coded
and logically appear when alternate channels are specified. Note that
the subordinate control unit blocks do not contain pointers to the
alternate channel blocks. Only the prime control unit block contains
pointers to the alternate RCHBLOKS. This is consistent with the current CP block structure. RCTLUNIT ADDRESS=340,CUTYPE=3830,FEATURE=32-DEVICE,ALTCH=(1,2,4) RCHANNEL ADDRESS=1,CHTYPE=MULTIPLEXOR RCHANNEL ADDRESS=2,CHTYPE=MULTIPLEXOR RCHANNEL ADDRESS=3,CHTYPE=MULTIPLEXOR RCHANNEL ADDRESS=4,CHTYPE=MULTIPLEXOR RCHAN1 RCHAN2 RCHAN3 RCHAN4 r->.- r->. r->. r->. I 1 I I I 1 I , L 1 L- , I I I RCU340 RCU350 I RCU348 RCU358 I • • i , , I I I I ----.I IRCUSUB 1 , 1 RCHAN3 RCUCHA I I I I I 1 L +-1 RCHAN1 RCUCHB IRCU340 I I I 1---1 L--IRCHAN2 RCUCHC I 1 1 1 I I RCHAN4 RCUCHD 1 I L ----, 1 L
Figure 13. Real I/O Control Block Structure for Alternate Channel
Specification
The following restrictions apply directly to Alternate Path processing: • VM/370 does not support alternate paths for devices
attention interrupts to invoke a read response from the
example, the 3851 Mass storage Control (MSC) unit.
that issue
host; for • All devices on one physical control unit must be defined as either
alternate path or no alternate path. There can be no splitting of
control units when dealing with alternate paths. 78 IBM VM/370 Planning and System Generation Guide

Saved Systems Saved Systems Saved systems are described in detail in the VftLJ70 2Y§tem Programmer's If you plan to save core-image copies of virtual machine
operating systems you should do the following when you generate Vft/370. • Create an entry in the system name table for each system you wish to
save. • Reserve space on a CP-owned volume for each system you wish to save. You create entries in the system name table by coding NAftESYS and NAMENCP macros and assembling the system name table (DMKSNT) file during
system generation. You specify which volumes are to be owned by CP by
coding the SYSOWN macro and assembling the CP system control (DMKSYS) file during system generation. These macros and files are described in Part 2.
If you decide to add entries to the system name table after you have
installed Vft/370, you must code the appropriate NAMESYS or NAMENCP macros, reassemble the system name table module (DftKSNT), and reload the CP nucleus. Likewise, if you must add a CP-owned volume after system
generation, you must recode the SYSOWN macro, reassemble the CP system
control module (DMKSYS), and reload the CP nucleus. Use the GENERATE EXEC procedure to reassemble DMKSNT and/or DftKSYS and to reload the CP nucleus. GENERATE is described in "Part 5. Updating VM/370." Part 1. Planning for System Generation 79