AA-L620A-TK StorageSysDiags

This document, "Storage System Diagnostics and Utility Protocol (DUP)," outlines the communication protocol used by Digital Equipment Corporation's mass storage systems for diagnostics and utility operations. It is specifically intended for programmers developing host DUP class drivers.

Key aspects of the DUP protocol include:

1. Purpose: Unlike the Mass Storage Control Protocol (MSCP) used for normal data transfer, DUP enables the host to load, start, monitor, and terminate diagnostic and utility programs (called "remote programs") running on the mass storage controller.
2. Communication Structure:
   • It defines a primary, asymmetric master/slave protocol between the host's DUP class driver and the controller's DUP server.
   • A subprotocol, the "Host Control Program/Remote Program protocol" (also known as the DUP Dialog), is embedded within SEND/RECEIVE DATA commands for interaction between the host application and the remote program.
   • Communication utilizes two services: sequential messaging (for control) and block data transfer (for data and program images).
3. DUP Server States: The DUP server operates in distinct states relative to the class driver: "Offline" (unavailable), "Available" (could connect but not synchronized), and "Online" (connected and synchronized), which further divides into "Idle" (not monitoring a remote program) and "Active" (a remote program is running).
4. Commands: DUP messages have a generic format with a header (including a command reference number, opcode, modifiers) and a parameter area. Key commands include:
   • ABORT PROGRAM: Terminates a remote program.
   • GET DUST STATUS: Queries the server's characteristics, state, and running program's status.
   • EXECUTE SUPPLIED PROGRAM: Loads and executes a program supplied by the host.
   • EXECUTE LOCAL PROGRAM: Instructs the controller to find, load, and execute a program from its local media.
   • SEND DATA / RECEIVE DATA: Used for two-way data and message transfer between the host and a running remote program.
5. Synchronization and Error Recovery: The protocol emphasizes re-synchronization between the class driver and DUP server as the primary method for error recovery, ensuring a known state where no commands are outstanding. Command timeouts are used to detect unresponsive controllers or programs.
6. Remote Program Characteristics: Remote programs, whether supplied by the host or local, have a "Remote Program Header" defining characteristics like size, overlay requirements, and whether they utilize the DUP Dialog for communication. A special "DIRECT" program exists to report a directory of local programs.

In summary, the DUP protocol provides a detailed framework for diagnostic and utility management, enabling robust interaction and control over software execution on Digital Equipment mass storage controllers.