mtcsr6

This document is an assembly language listing for MTCSR6 - Magnetic Tape Routines for 516 Control, copyrighted by Digital Equipment Corp. in 1969. Assembled on June 4, 1969, it provides detailed code for managing magnetic tape operations within a system that utilizes a 516 Control unit.

The document outlines a comprehensive set of magnetic tape service subroutines responsible for various functions, including:

• Initialization (MTCINI): Setting up the tape system and its parameters.
• Basic I/O Operations (MTIN, MTOUT): Handling data input and output to magnetic tape.
• Device Control: Functions such as releasing tape units, closing input/output channels, renaming, and clearing tape units.
• Special Tape Operations: Routines for dumping data (MTOMPO, MTOMPI), writing end-of-file markers, performing BACKSPACE operations, and REWINDING the tape.
• Error Handling: Extensive mechanisms for detecting and managing various errors, including hung timeouts, parity errors, data missed, illegal operations, write-locked conditions, and end-of-tape conditions. The code maintains cumulative error and record counters within the Magnetic Tape Control (MTC) Device Data Block to track device status.
• System Integration: Interfacing with the operating system through User Unimplemented Operations (UUOs) to define legal tape commands. It also includes clock-level routines (MTCLOK) for monitoring asynchronous tape operations like rewinding and managing the detachment/attachment of Magnetic Tape Control (MTC) and Data Control (DC) units.
• Device Data Block (MTCDDB): Defines the structure and flags for managing magnetic tape devices, including specific bit-level definitions for error types and status.

The routines are designed to handle control flow, check device availability, manage data transfers, and include specific modifications to support the 545 Transport hardware. The document concludes with a symbol table, listing all internal and external symbols, highlighting the modularity and interconnections of these magnetic tape routines within the larger 516 Control system.