Design Specification for the Systems Communications Architecture

This document provides a design overview for the TOPS-20 implementation of the Systems Communications Architecture (SCA) protocol. It is organized into two primary sections:

• SCAMPI (Monitor SYSAP support): Covers major data structures like the System Block and Connect Block, interrupt handling, buffer management routines, and periodic function handlers like 'idle chatter' and buffer threshold management.
• SCSJSY (User-mode SYSAP support): Describes the user interface to the CI via SCA, including service request handlers (for sending packets and reading counters), buffer allocation within a dedicated virtual section, and the circuitous interrupt event handling process involving the scheduler and the Process Structure Block (PSB).

The document acts as a map for developers to understand the high-level flow and interlock mechanisms within the SCA implementation.