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8 VM/HSC 6.0 System Programmer’s Guide
1st ed., 6/30/04 - 312579601
Task Management
Multi-tasking is provided by the SCP to support the MVS-type task requests such as
POST, WAIT, ATTACH, etc. that the HSC expects. All modules are made resident at the
time of initialization. Also included in this component is the processing of System
Management Facility (SMF) records for output to a spool file.
Job Management
Most utilities are executed within the SCP environment as batch jobs punched by other
virtual machines. Special job statements define both the resources to be used and the
parameters to be passed to the desired program.
Processor Management
This component handles the resources of the virtual processor, including:
• interrupt handlers
• timer management
• IUCV paths and messages
• event tracing.
This component also handles authorization checking and PSW mode changing. Interrupts
consist of common processing, a first level handler which usually sorts out the interrupt
subtypes, and a second level handler which does the bulk of the processing. Timer services
include the TOD clock, the TOD clock comparator, and the CPU timer. Tracing includes
an internal table and a task which writes records to a spool file.
Communication
Standard MVS-type WTO/R and related operator communications are also supported,
with limitations on the routing and descriptor codes. The QEDIT interface, ECBs, and
various queues provide for inter-task communication.
Inter-Machine Communication
The Inter-User Communication Vehicle (IUCV) is a closed-loop technique used in VM to
communicate between users. A user sends an IUCV message and waits for a reply. This
service is used to transfer data between the HSC and the TMS.
Additionally, IUCV is used to access the BLOCKIO and MESSAGE system services. The
message service (*MSG) is used to intercept SMSG communications from operators.CP
DASD BLOCKIO forms the foundation of the SCP BDAM access method. BLOCKIO
reads and writes data to any DASD device with device independence, but the SCP must be
aware of the device type, especially when the data set is shared with an MVS host.