RSCS Supervisor
The first 4K bytes of contain hardware and supervisor-defined
constants, control areas, and supervisor service routines. The first bytes of are defined by System/370 architecture and contain hardware-defined constants. This area is
initialized by the DMTINI routine at initial program load time.
The rest of DMTVEC, 112 bytes, contains supervisor-defined addresses
and constants used for dispatching, storage maPfin9, queue management,
and task management. DMTMAP: The supervisor storage area contains the main storage map and the-fIrst extent of the supervisor queue.
The main storage map is a table comprising one byte for each page in
accessible storage. Each byte displacement in the table implies an
associated main storage number.
The supervisor queue is a chain of 16-byte elements, formatted during
initialization, maintained by the DMTQRQ routine, and containing the
status information for all system tasks running or waiting to be
dispatched. The length of this chain is such that the service routines
that follow are located at the end of the page of storage. ftgy!!ng§: The rest of the supervisor contains service
routines that provide services to other system tasks, as follows: DMTEXT DMTSVC DMTIOM DMTQRQ DMTDSP DMTWAT DMTPST DMTASK DMTSTO DMTASY DMTSIG DMTGIV DMTAKE
Function Handle-external interruptions
Handle SVC interruptions
Handle I/O interrupts and requests
Manage the supervisor status queue
Dispatch eligible tasks Suspend task execution Signal completion of an event
Create and delete system service tasks
Reserve and release main storage pages
Provide asynchronous task to task exits
Interrupt a task, immediately, for an ALERT request
Enqueue a GIVE request element for another task
Process a GIVE request element
Supervisor Queue Extension
The supervisor queue extension is a chain of 16-byte elements that
provide an extension to the supervisor queue located in DMTMAP. Free Storage
This area of free storage is managed by the module. Syste. tasks
reserve and release virtual storage in full page increments as required. Part 4. Remote Spooling Communications Subsystem (RSCS) 333
System Control Task
The system control task consists of
nonexecutable modules, as follows:
five executable and two DMTREX Handle console I/O; process request elements for service routines; terminate system service and line driver tasks.
DMTCRE DMTCMX DMTMGX DMTCOM DMTMSG DMTSYS Start a line driver task and create the rMTAXS and DMTLAX tasks during initialization.
Handle all console functions.
Build and forward message request elements. Perform miscellaneous system service functions.
Table of message texts and codes.
Link table, file tag storage area, tag queue pointers,
and switched line port table.
Free Storage and Line Drivers
This area of free storage is also managed by DMTSTO. In addition to
providing storage for system tasks, it is used for line driver storage.
For each active link that is initialized by DMTCRE, a copy of a DMTSML or DMTNPT line driver is brought into virtual storage. Line driver
storage is assigned downward from X'7COOO', in four-page increments.
Free storage for system tasks is assigned upwards from the page boundary
following DMTSYS, in one-page increments.
Line Allocation Task
The DMTLAX module allocates a line port to a link when its line driver
task is started. If a line address has been previously assigned in the
link definition or is specified in the START command, DMTLAX verifies
that the line is for a valid device type and is not already in use. If
a line address has not been previously assigned and is not specified in
the START command, DMTLAX scans the table of switchable line ports fer
an available line and assigns it to the link's line driver task. If a
line is not available or is incorrectly specified, an error message is
issued to the RSCS operator. Spool File Access Task
The DMTAXS module accepts files from the VM/370 spool system and
maintains the queues of main storage file tag slots; executes the ORDER, CHANGE, and PURGE commands; and opens and closes input and output VM/370 spool files.
334 IBM VM/370 System programmer's Guide
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