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
3800 Image Library
Generating a VM/370 System that Supports
the 3800 Image Library
The generation of a 3800 image library that runs under the control of VM/370 is normally done after the VM/370 system generation is completed.
However, when a 3800 image library is to be generated, the following
preparations must be made: An RDEVICE macro instruction for the 3800 printer must be included in
the real I/O configuration (DMKRIO) file. The 3800 image libraries that are to be used by VM/370 must be stored
on a CP-owned volume in the page format that is currently used for
saved virtual machine systems (that is, those created by the SAVESYS command). All 3800 image libraries in the system name table (CP module DMKSNT) and saved with the IMAGELIB command. Enough space to contain the 3800 image library must be allocated on
the CP-owned volume specified in the NAME3800 macro instruction.
Coding the RDEVICE Macro
The RDEVICE macro is described in Part 2. However, the format of the RDEVICE macro for a 3800 is included here to help you code the macro
correctly. The format of the RDEVICE macro for an IBM 3800 is:
r I Name Operation Operands
1--------------- I I RDEVICE ADDRESS= ccu, DEVTYPE=3800, [FEATURE=4WCGMS,] [IMAGE=imagelib,]
[ CHARS=ffff, ]
[FCB=lpi g ] , 1 , ! I [ DPM SIZE=n, ]
L
ADDRESS=cuu is the real device address (cuu) of the 3800. DEVTYPE=3800 is the device type. PEATURE=4WCGMS is a 3800 device with 4 Writeable Character Generation
Modules.
IMAGE=imagelib is the image library to be used by the 3800 printer
device after a cold start if none is specified on the
ST ART command.
CHARS=ffff
FCB=lpi
is the character arrangement table for the 3800 printer
device to be used after a cold start if none is specified
on the START command.
is the FCB to be used for the page separator for the 3800 printer device after a cold start if none is specified on
the START command. Part Planning for System Generation 69
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