PHYMVR Nov84

This document describes the TOPS-20 MSCP Server, PHYMVR, a module responsible for providing access to massbus disks across the CI-20 interconnect within the TOPS-20 operating system.

Key aspects of PHYMVR include:

• Architectural Position: It acts as an intelligent disk controller for the TOPS-20 MSCP driver (PHYMSC), interfacing as a device-independent disk driver (DSKOP Jsys). It operates at a level above physical I/O (PHYSIO) but below file system management, having no knowledge of file system formats. It is an SCA SYSAP, communicating with the MSCP driver using the TOPS-20 SCA interface.
• Limited MSCP Implementation: PHYMVR implements only a subset of the full MSCP functions, supporting only what is required for PHYMSC's operation. This means certain unit flags, controller flags, command modifiers, and MSCP functions (e.g., shadowing, caching, tape device services, error logging datagrams, specific write/read commands) are either unsupported, ignored, or partially supported.
• Administrative Control: System administrators can manage which disk drives are accessible through PHYMVR using the SETSPD program with new ALLOW and RESTRICT commands (invoked via the SMON% Jsys). By default, all disks are initially restricted.
• Operational Details: The server is a generally passive, interrupt-driven device responding to MSCP driver requests. It requires the TOPS-20 Common File System to be in use. It communicates through the PHYSIO interface for disk operations and relies on SCAMPI services for inter-process communication. Periodic checks ensure connection integrity and broadcast availability messages.
• Data Structures: It modifies and uses specific bits within the TOPS-20 Unit Data Blocks (UDBs) and I/O Request Blocks (IORBs) to manage disk status and connection information.

The document also details error handling (no direct error log datagrams, IORB error mapping), unit number calculation, and the impact of PHYMVR on existing system documentation.