IAS Guide to Writing a Device Handler Task

This manual provides instructions for system managers and programmers on creating device handler tasks for non-standard peripheral I/O devices within the IAS (Interactive Application System) operating system.

Key topics covered include:

• Handler Task Architecture: The five basic sections of a device handler, including table areas, initialization code, I/O service routines, interrupt service routines (ISR), and power failure recovery.
• Communication and Data Structures: How handlers interface with the system using Unit Identification Tables (UIT) and Dispatch Tables, and how they utilize system data structures like the Physical Unit Directory (PUD) and System Task Directory (STD).
• Initialization and Linking: Requirements for declaring a handler as resident, connecting to interrupt vectors, and the procedures for linking tasks using the Task Builder.
• I/O Processing: Details on dequeuing I/O requests, handling different I/O functions, and managing error logging.
• Advanced DMA Support: Specialized guidance on handling Direct Memory Access (DMA) devices, including UNIBUS mapping register (UMR) support for PDP-11/44 and PDP-11/70 systems.
• System Subroutines: An extensive reference (Appendix A) of IAS subroutines used by handlers for tasks like node handling, event flag management, and task swapping.