MSCP Server

The MSCP server acts as an intelligent disk controller for TOPS-20, interfacing as a device-independent disk driver (like DSKOP Jsys) at a higher architectural level than PHYSIO, but without file system knowledge. Its primary user is the TOPS-20 MSCP driver (PHYMSC).

The server's main functions involve managing communications via the Systems Communications Architecture (SCA) and processing commands. It passively establishes SCA connections, listening for "MSCP$DISK" and accepting connections from specific "KL" connectors. Connections exist in various states (e.g., Listen, OK to Send, Shutdown) and can terminate due to port errors, remote system disappearance, driver requests, or server-detected timeouts.

All commands are SCA messages, processed based on their opcode. Commands that cannot be immediately completed, such as READ/WRITE operations or those failing to send end packets, are queued in doubly linked lists and progress through specific states (e.g., Queued, Aborted, IORB active). The server also implements connection and command timeouts to handle unresponsive connections or commands, which can lead to connection shutdown.

The MSCP server interacts with other system components:

• PHYSIO: Utilized for scheduling I/O Request Blocks (IORBs) and disk transfers, particularly for complex READ and WRITE commands that involve acquiring memory pages and initiating named buffer transfers.
• SCA Interface: Handles various callbacks for message reception, connection events, and buffer transfer completions.
• Periodic Check: A routine run every 10 seconds to monitor active connections for timeouts, retry queued commands, and send status messages.
• SMON/TMON/SETSPD Interface: Provides a user interface to manage massbus disks, allowing drivers to restrict or allow disk usage and receive "AVAILABLE ATTENTION MESSAGES" when new disks come online.

Key data structures, such as the MSCP Server Data, Queued Command Header, and Server Connection Data Block (SCDB), store essential information about server status, connections, and command states.