lptser

This document describes LPTSER (Line Printer Service Routine), a MACRO assembly program developed by Digital Equipment Corporation (DEC) in 1969 for managing multiple line printers on a DEC system.

The routine's core functions include:

• Initialization (LPTINI): Setting up each individual line printer at system startup, clearing its state, and deassigning interrupt channels.
• Output (LPTOUT): Handling requests to print data, managing output buffers, and initiating I/O operations.
• Interrupt Service (LPTINT): Processing hardware interrupts from the printers, advancing printing, handling job completion, and managing buffer pointers.
• Error Handling (LPTERx): Responding to and logging printer errors, and attempting recovery.
• Device Control: Providing routines for closing (LPTCLS) and releasing (LPTREL) printer resources, and addressing "hung" device conditions (LPTHNG).

Each line printer managed by LPTSER utilizes a Device Data Block (DDB) to store its control and status information, with specific mnemonics defined for various hardware flags (e.g., busy, done, error, clear buffer). The routine also defines and references external symbols, indicating its integration with other system components for common memory, clock services, error control, and User Unimplemented Opcodes (UUOCON) management.