INITIALIZATION AND TERMINATION
After CP has been initialized, DMKCPVEN enables the communication lines
in response to the ENABLE command. Then an individual virtual machine
is attached to the system, using the following steps:
1. When the CP receives the initial interrupt from a terminal on an
enabled line (normally initiated by a user dialing in On a
data-set), the DMKCNSIN routine is entered. DMKCNSIN determines
the terminal device type, stores this information in the terminal device bleck, writes the online message and puts the terminal line
in a state to receive an attention interruption.
After the online message has been displayed at the user's terminal,
and he has pressed the ATTENTION key, DMKCNSIN (the console
interruption routine) calls DKKBLDV8 to build a skeleton VMBLOK for
the user. At this time, the userid is LOGONxxx, where xxx is the
terminal real device address, and a flag is set to indicate that
the user has not yet completed the logon process.
Then DMKCNSIN calls which types a single blank at the
terminal, and issues a read to the terminal for the user to enter
his first command (normally LOGON or DIAL).
After the first command has been entered by the user, DMKCNSIN further determines the type of terminal. If the terminal is a
2741, DMKTRMID is called to identify it as either a 2741P
(PTTC/EBCD) or a 2741C (Correspondence) terminal. If successful,
the correct device type and translate tables for input and output
are set; if fiot, flags are set to indicate that the terminal is
not yet identified.
Then control is returned to DMKCFMBK, which determines if the first
command is valid (for example, LOGON, ftSG, or DIAL). If the first
command is not valid, a restart message is given, and the read to
the terminal occurs again for the first command. If the first
command was LOGON (or its abbreviation), DMKLOGON is called to
complete the process of attaching the virtual machine to the
system.
The operations performed by DMKLOGON include the following: • Ensures that the maximum number of virtual machines allowed on
the system is not being exceeded. • Obtains the userid from the command line, and chects for a
possible password and other optional operands. • Checks the userid and password (entered separately if not on the LOGON command line) against entries in CP's directory of users. CP Introduction 1-123

• Ensures that the
error condition),
disconnect mode. user is not logged on at
or reconnects the user
another terminal (an
if he was running in • Obtains pertinent information on the user's virtual machine from the user machine block portion of the directory. • Stores the correct userid (replacing the LOGONxxx userid used
until now), virtual storage size, and other vital information in
the virtual machine's VMBLOK. • Allocates
(necessary
storage).
and
for
initializes segment, page,
handling of the virtual
and swap
machine's
tables
virtual • Schedules MSS volume mounts for any required MSS volumes if the MSS is available and the volume is not already mounted. • Allocates an extended VMBLOK (ECBLOK) if the user's virtual
machine has the ability to run in the extended control mode. • Allocates and initializes virtual device blocks, control unit
blocks, and channel blocks, using information from the user
device blocks portion of the directory. • Establishes links (as feasible) to all DASD devices included in
the directory, the accessibility of any disk being determined by
the user access mode in the directory, and whether any other
users are presently linked to the disk, in read mode and/or
write aode. • Initializes all other virtual device blocks as appropriate, such
as reader, punch, printer, and terminal. • Maps all virtual devices to real devices. • Performs appropriate accounting. • Informs the user of the date and time of the aost recent
revision to the system log aessage (LOGMSG), and of the presence
of any outstanding spooled files in his virtual reader, printer,
or punch. • Sends a ready message to the user with the date and time (and
weekday), and a aessage to the system operator indicating that
the user has logged on.
If the virtual aachine has a device address or a named system in the
directory and the initialization was not suppressed via an option on the LOGON command line, then that device or named system is then loaded (via 1PL) at the conclusion of the logon process. Otherwise, when the logon
functions are complete, the user's terminal is placed in CP read mode ready for the entry of his first desired command. Under the latter condition of no automatic IPL, the user can 1Pt an
alternate nucleus by using the STOP option in the IPL coa.and. This
option causes the normal IPL procedure to halt execution prior to
loading the initial PSi, and issues a DIAGNOSE code 8 that places the
user's terminal in CP read mode. A hexadecimal character entered in
location X'08' changes the nucleus naae. A hexadecimal character
entered in location X'09' changes the apparent storage size. The BEGIN coamand allows the 1PL procedure to continue.
1-124 IBM VM/370 System Logic and Problem Determination--Volume 1