MSCP Driver

This document details the PHYMSC driver, a TOPS-20 device driver designed to function as an intermediate layer for the CI-20. Its primary role is to integrate MSCP (Mass Storage Control Protocol) disks with the PHYSIO system, communicating with HSC50 disks using SCA (Systems Communication Architecture) and MSCP protocols. The PHYMSC driver operates as a "Kontroller" within the PHYSIO system.

The document outlines the driver's structure, services, and its relationships with other CI-related services and the overall monitor. Key responsibilities include:

• Coordinating all access between PHYSIO and MSCP disks.
• Maintaining the interface between MSCP disks and the PHYSIO system, including locating, recognizing, and managing remote disks.
• Ensuring the functionality of remote servers and initiating reloads in case of failure.

The driver's core components include a Poller for recognizing new servers and detecting failures, Interrupt Service routines (SCA Callbacks) for handling asynchronous events and I/O completion, and a PHYSIO Interface for managing Start I/O requests and other Kontroller responsibilities.

The operational description covers:

• Initialization: A multi-step, interrupt-driven process involving connecting to remote systems, determining device characteristics, and bringing disk units online.
• Poller Functions: Regularly checking for new nodes, monitoring server health, attempting to online offline drives, and re-establishing connections with failed HSC servers.
• Start I/O: Processing requests from PHYSIO, including validation, resource allocation, address conversion, and queuing requests to SCA, with mechanisms to handle credit availability.
• Error Handling: Mechanisms for managing buffer allocation failures, various data errors (which are mapped to PHYSIO errors), server failures (expected to be resolved by server dis-connect/re-connect/re-initialization), and lack of communication credit.
• Interrupt Services: A detailed breakdown of SCA Callbacks used for error logging, connection management, node status changes, credit availability, and processing MSCP messages.

The document also mentions support for dual-port disks via the HSC50 and notes that code for tape service and RA60 drives exists but is currently untested and inaccessible, intended for future development. Configuration support is stated for 16 CI nodes and 24 units per node.

Overall, this document serves as a "road map" for implementors, detailing how the PHYMSC driver implements its functional specification, its internal workings, and its interactions with other system components.