VAXELN

This document, the "VAXELN User's Guide" (First Edition - March 1985, Software Version 2.0), serves as an introduction and user's guide to the VAXELN toolkit. It is designed for programmers and students with a working knowledge of Pascal or C programming and a basic understanding of VAX/VMS DCL.

VAXELN Overview: VAXELN is a software product for developing dedicated, real-time systems on VAX processors. Its development tools run on VAX/VMS and MicroVMS operating systems. Key capabilities and features of VAXELN include:

• High-Level Programming: Supports development entirely in high-level languages like VAXELN Pascal and C.
• Minimal Operating System "Overhead": Operates with a small kernel executive directly on VAX hardware, managing system resources and data.
• Concurrent Programming: Enables multitasking (multiple parts of a program executing concurrently) and multiprogramming (multiple programs executing concurrently).
• Transparent Network Support: Provides data communication between VAXELN jobs (and with other DECnet systems) across a network.
• File Service: Supports I/O operations to local and remote file storage devices, using a file structure compatible with VAX/VMS (Files-11).
• Program Development & Debugging: Tools run on a VAX/VMS host, allowing remote or local debugging of target systems.

Document Structure and Key Topics:

The guide is organized into 15 chapters and 4 appendices, covering the following main areas:

1. VAXELN Concepts (Chapter 1): Introduces what VAXELN is, its core capabilities, the structure of a VAXELN system (host and target machines on Ethernet, jobs, processes), and dynamic program loading. It also includes a walk-through example of building, down-line loading, and executing a simple VAXELN application.
2. Kernel Objects (Chapter 2): Describes the types of objects managed by the VAXELN kernel (PROCESS, AREA, EVENT, SEMAPHORE, MESSAGE, PORT, NAME, DEVICE), their properties, operations, and internal representation.
3. Processes and Jobs (Chapter 3): Details jobs as process families, process states (running, ready, waiting, suspended), job and process scheduling priorities, memory management (PO/P1 regions, stacks), and interjob data sharing using AREA objects.
4. Synchronization (Chapter 4): Explains the WAIT procedures for coordinating processes, events, semaphores (binary and counting) for resource control, and time representation.
5. Interjob Communication (Chapter 5): Covers message passing as the primary means of interjob communication, including MESSAGE and PORT objects, named message ports, message transmission methods (datagrams and circuits), and flow control.
6. I/O Devices and Interrupt Handling (Chapter 6): Discusses handling device interrupts, Interrupt Priority Levels (IPLs), Direct Memory Access (DMA) device handling, and device register procedures.
7. The Network Service (Chapter 7): Describes the VAXELN Network Service, its use of DECnet protocols for network applications, application message services, name servers (for universal names), and communication with non-VAXELN nodes.
8. System Security (Chapter 8): Outlines optional security features, the Authorization Service (for user authentication and resource protection), and File Service security features including User Identification Codes (UICs) and protection masks.
9. The File Service (Chapter 9): Provides a comprehensive look at disk and tape file services, device specifications, volume names, file specifications, the File Access Listener (for remote file access), and the Data Access Protocol (DAP) used by device drivers.
10. Device Drivers (Chapter 10): Details the features of supplied VAXELN device drivers for disk, tape, printer, terminal, and real-time devices, including their characteristics and logical I/O.
11. Exception Handling (Chapter 11): Explains synchronous and asynchronous exceptions, the VAX stack architecture in relation to exceptions, exception handler arguments, "continue" and "resignal" operations, and message processing features for status codes.
12. Program Development (Chapter 12): Summarizes the use of VAXELN Pascal and C compilers, and the VAX/VMS librarian and linker for preparing program images.
13. System Development (Chapter 13): Describes the VAXELN System Builder (EBUILD command) for combining program images into a bootable system, including configuring system, program, device, network, terminal, and console characteristics.
14. Booting and Down-Line Loading (Chapter 14): Explains procedures for booting VAXELN systems from disks and for down-line loading systems onto target machines via Ethernet, including configuration steps.
15. Debugging (Chapter 15): Covers local and remote debugging methods provided by the VAXELN development system, including general debugger concepts, syntax rules, and a detailed summary of debugger commands.

Appendices (A-D): Provide additional technical information, including VAX-11/750 microcode patches, internal call notation for kernel procedures, a list of status values and exception names, and performance evaluation data for VAXELN on a MicroVAX I system.