mtasrx

This document is an assembly language listing for MTASRX (Magtape Routines for PDP-10, Version V420), developed by Digital Equipment Corporation in 1969.

It details a sub-program designed for low-level interaction with magnetic tape units on the PDP-10 computer. Key functionalities include:

• Initialization and Control: Routines for initializing (MTAINI), connecting (CONECT), and releasing (MTAREL) tape drives.
• Data Transfer: Functions for input (MTIN) and output (MTOUT) operations, including dump mode (MTDMPI, MTDMPO).
• Tape Management: Operations such as closing (MTCLOS), rewinding (REWCHK, HUNGTP), and handling logical end-of-tape (LEOT).
• Error Handling: Extensive mechanisms for detecting and responding to errors, including retries (RETRY, TRYAGN), handling hung devices, and managing error flags (ERRFLG).
• Device Status and Configuration: Routines to check tape readiness (RDYCHK), set device parameters (e.g., 7-track or 9-track modes via SET9TK), manage interrupts (MTAINT), and handle I/O status.

The document provides the assembly code with comments, defining entry points (MTASRX), dispatch tables (MTADSP) for various tape operations, and internal routines that manage the intricate details of magtape hardware control, buffering, and system-level interactions.