DMSSET initializes the C"S/DOS operating environment as follows: Verifies that the mode, if specified, is for a DOS formatted disk. Stores appropriate data in the SYSRES LUB and PUB. Locates and loads the CMS/DOS discontiguous shared segment. Saves (in NUCON) the addresses of the two major CMS/DOS data blocks, SYSCOM, BGCOM,and the address of the CMS/DOS discontiguous shared
segment (C"SDOS). Sets the DOSMODE and DOSSVC bits in DOSFLAGS in NueON. Assigns (via ASSGN) the SYSLOG logical unit as the CMS virtual
console.
The CMS/DOS operating environ.ent is entered when the CMS SET DOS eN i& invoking the Several data areas are prepared for processing during initialization.
The .ain CMS data area, NUCOH, is modified to contain the addresses of
two DOS data areas, SYSCOM and BGCOM. The SYSCOM DSECT is the DOS system communications region. It
consists mainly of address constants, including the addresses of the AB
option table, the PUB ownership table, and the FETCH table. It also
includes such information as the number of partitions (always one for CMS/DOS) and the length of the PUB table.
The BGCOM DSECT is the partition communication region. It includes
such information as the date, the location of the end of supervisor
storage, the end address of the last phase loaded, the end address of
the longest phase loaded, bytes used to set the language translator and
supervisor options, and the addresses of many other DOS data areas such
as the LUB, PUB, NICL, FICL, PIB, PIB2TAB, and the PCTIE. The LUB and PUB tables are also made available during initialization.
The LUB is the logical unit block table. It acts as an interface
between the user's program and the CMS/DOS physical units. It contains
an entry for each sy.bolic device available in the system.
Each of the symbolic names in the LUB is mapped into an element in
the PUB, the physical unit block table. The PUB table contains an entry
for each channel and device address for all devices physically available
to the system and also contains such information as device type cede, eMS disk mode, tape mode setting, and 7-track indicator.
Two bits are set in DOSFLAGS in NUCOH, DOSHODE and DOSSVC. DOSMODE specifies that this virtual machine is running in the eMS/DOS operating
environment. DOSSVC indicates Whether OS or DOS SVCs are operative in
the operating environment. If DOSSVC is set, DOS SVCs are used;
otherwise, as SVCs are operative.
2-138 IBM VM/370 System Logic and Program Determination--Volume 2
SETTING OR RESETTING SYSTEK ENVIRONMENT OPTIONS Once the CKS/DOS environment is initialized, the flags and control
blocks set during initialization can be modified and manipulated to
perform the functions specified by commands entered at the console.
This section describes the modules that set and reset the system environment options. That is, they set those options that control
co.piler execution and that control the configuration of logical and
Fhysical units in the system.
The CKS/DOS OPTION command invokes module DKSOP!, which sets either the
default options for the compiler or the options specified on the command
line. The ncnstandard language translator options switch and the jcb
duration indicator byte are altered. Options are set using two control
words located in the partition communication region (EGCOM). Bits in
bytes JCSW3 or JCSW4 are set, depending on the options specified. Module DMSASN is invoked when the ASSGB command is entered. DKSASN first scans the command line to ensure that the logical unit being
assigned is valid for the physical unit specified (for example, SYSLCG must be assigned to either the virtual console or the virtual printer). Once the command line is checked, PUB and LUB entries are modified to
reflect the specified assignment.
For the PUB entry, the device type is determined (via DIAG 24) and
the device type code is placed in the PUB. Other modifications are made
to the PUB depending on the specified assignment. The LUB entry is then
mapped to its corresponding PUB. The function of DMSLLU is to request a list of the physical units
assigned to logical units. It performs this function by referencing
information located in the CMS/DOS data blocks, specifically LUB, and PUB. Another data block, the next in class (NICL) table is
also referenced.
The information on the com.and line is scanned and the appropriate items are displayed at the user's console. If an option (EXEC or APPEND) is specified, an EXEC file is created ($LISTIO EXEC A1) to
contain the output. If EXEC is specified, any existing $LISTIO EXBC 11 file is erased and a new one is created. If APPEND is specified, the
new file is appended to the existing file. CKS Method of Operation and Program Organization 2-139
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