ptysrh

This document is a MACRO assembly language listing for "PTYSRH: Half Duplex Pseudo Teletype Service Routines," developed by D. Witcraft/RAP for Digital Equipment Corporation, dated June 4, 1969.

The code defines and implements the core software functions for managing a pseudo (simulated) teletype device operating in half-duplex mode. It serves as a low-level driver or operating system component, handling input and output for virtual terminals.

Key functionalities and components include:

• Initialization: Setup of accumulator assignments, definition of device-dependent I/O status bits (e.g., IOPTW for output wait, IOPTRE for response ready, MONMOD for monitor mode).
• Output Routine (PTYOUT): Manages character transmission, output buffers, handling responses from the pseudo teletype, and setting relevant status flags for the "object job" (application) interacting with the device.
• Input Routine (PTYIN): Handles the processing of incoming characters and managing input buffers.
• Synchronization (PTWAKE, PTYPE): Includes routines to intercept TTY output at the UUO (User-User-Output) level to synchronize it with pseudo teletype input, likely involving a system clock.
• Status Management (PTYSET, PTYMNMD, PTYOW): Routines for setting various internal status bits related to the pseudo teletype's operational state, such as monitor mode or output wait.
• Context Saving/Restoration (PTYSAV, PTYRET): Functions to preserve and restore the state of accumulators (registers) and I/O registers during operations, crucial for multi-tasking or interrupt handling.
• Data Structures: Defines the "Pseudo Console Device Data Block" (PTYDDB), which stores information about each pseudo teletype unit.

The document provides detailed assembly code, comments explaining logic, accumulator assignments, status bit definitions, and a symbol table. It describes how the routines interact with system components like TCOMM (teletype communication) and TTYTAB (teletype table) to provide a robust pseudo teletype service.