Shared-Memory Objects

6.1 Introduction

VxMP is an optional VxWorks component that provides shared-memory objects dedicated to high-speed synchronization and communication between tasks running on separate CPUs. For information on how to install VxMP, see Tornado Getting Started.

Shared-memory objects are a class of system objects that can be accessed by tasks running on different processors. They are called shared-memory objects because the object's data structures must reside in memory accessible by all processors. Shared-memory objects are an extension of local VxWorks objects. Local objects are only available to tasks on a single processor. VxMP supplies three kinds of shared-memory objects:

shared semaphores (binary and counting)

shared message queues

shared-memory partitions (system- and user-created partitions)

Shared-memory objects provide the following advantages:

A transparent interface that allows shared-memory objects to be manipulated with the same routines that are used for manipulating local objects.

High-speed inter-processor communication--no unnecessary packet passing is required.

The shared memory can reside either in dual-ported RAM or on a separate memory board.

The components of VxMP consist of the following: a name database (smNameLib), shared semaphores (semSmLib), shared message queues (msgQSmLib), and a shared-memory allocator (smMemLib).

This chapter presents a detailed description of each shared-memory object and internal considerations. It then describes configuration and troubleshooting.