3704/3705 Control Program For each physical 3704/3705, there should be only one RDEVICE macro
which specifies the ADAPTER=TYPE1, TYPE2, TYPE3, or TYPE4, MODEL, CPTYPE, and CPNAME operands. This RDEVICE macro defines the base
address of the 3704/3705 (that is, the real address used to perform the
load and dump operations). If the physical device is a 3705 with two
channel adapters installed, there may be a second RDEVTCE macro that
specifies the ADAPTER=TYPE1, TYPE2, TYPE3, or TYPE4, MODEL, and CPTYPE operands. There must a second use of the CPNAf!E o-perand. --Even
if CPTYPE=EP is specified, the 3704/3705 base address cannot be used as
a telecommunication line; its function is only to load and dump the 3704/3705, and the device type and class are different from those of all
other lines generated. Whenever there is more than one subchannel address (CPTYPE=EP); include in the DMKRIO deck all of the RCTLUNIT macros required to
specify those real addresses which the EP control program may use.
If you have a 3704/3705 and a 2701/2702/2703 on the same V"/370 system, the virtual addresses for the 3704/3705 must not be the same as
any of the real 2701/2702/2703 addresses.
Examples of RDEVICE macro specifications follow. For convenience, the
continuation character in position 72 is not shown. RDEVICE ADDRESS=(020,16), DEVTYPE=3704, MODEL=A2, ADAPTER=TYPE1, CPNAME=CEP020 This describes a 32K 3704 at address X'020', with 15 emulator lines
addresses X'021' to X'02F' and with the default parameter of
ADAPTER=IBM1 and SETADDR=4. The 3704 is to be loaded with the
Emulation Program 'CEP020'. RDEVICE ADDRESS=(030,16), DEVTYPE=3704, ADAPTER=IBM1,
SETADDR=2,
B ASEADD=02-0 This describes an additional 16 emulator lines on the same 3704 specified by Example 1. Part 1. Planning for System Generation 67
3704/3705 control Program
Creating an Entry in the System Name Table It is necessary to create an entry in the system name table (D"KSNT) for
each unique 3704/3705 control program that you generate. If you can
foresee generating several versions of the 3704/3705 control program,
define extra entries in the system name table when you generate V"/370. In this way, you need not regenerate the VM/370 system just to update
the system name table. If you should have to regenerate the VM/370 system just to add a new entry to the system name table, see the
discussion about the GENERATE EXEC procedure in "Part 5. Updating VM/ 370. " The NAMENCP macro is described in Part 2.
Reserving DASD Space for the 3704/3705 Control Program Image DASD space to contain the 3704/3705 control program image must be
reserved on a CP-owned volume. The DASD space reserved should be
sufficient to contain the number of pages specified in the SYSPGCT operand of the NAMENCP macro, plus one or more for system use, as
follows: • If CPTYPE=EP, allow only one extra page.
These additional pages are used to store the reference table
information provided by the SAVENCP program. Alternate Path Support Alternate path logic provides support for the two channel switch and
two-channel Switch Additional Feature and the String Switch Feature by V"/370. This support allows up to four channels on one control unit to
be attached to V"/370 and/or one device to be attached to two logical
control units. This allows the control program up to eight paths to a
given device when the maximum number of alternate channels and alternate
control units are specified. When an I/O request is received for a
device, V"/370 can select a free path from any of the available paths to
the device. With this support, even though the primary path to a device
is busy, there may exist an alternate path(s) that is available.
Instead of the I/O request being queued, it can be initiated immediately
on an alternate path. In the case where no available path to the device
exists, alternate path I/O scheduling is implemented in such a way that
the request is queued off multiple busy/scheduled paths and the first
path to become available will be the path the I/O is started on. This
approach has some distinct advantages over approaches used by other
operating systems:
1. The I/O starts on the first available path to the device. This
eliminates the arbitrary choice of queuing based on number of IOBLOKs already queued, primary path, last busy scheduled path
encountered, etc.
2. No single user is penalized more than any other user.
3. The first in, first out (FIFO) principle is adhered to.
An example of alternate path usage is shown in the section "3850 "ass Storage System" later in Part 1. 68 IBM V"/370 Planning and System Generation Guide
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