Message Queues
Input/Output Methods 6-21
Note: This document does not discuss how to write an allocator.
Information about designing allocators and transports will be provided in a
future document.
An application can use multiple allocators. The purpose of having multiple
allocators is to allow an application to regulate its message usage. For
example, an application can allocate critical messages from one pool of fast
on-chip memory and non-critical messages from another pool of slower
external memory.
6.5.4 Transports
The job of the transport is to communicate across a physical link to another
processor. The transport interface allows you to change the underlying
communication mechanism without changing the application (except for the
configuration of the transport).
A transport is an instance of an implementation of the transport interface.
There is an array of transports on each processor. There is at most one
transport between any two processors. This array is based on processor IDs.
So the first element (the 0th index) of the transport array on each processor
contains the transport to processor 0. On processor 0, the first element is a
MSGQ_NOTRANSPORT transport that is never used.
For example, consider the system shown in the following figure, in which
three processors are running DSP/BIOS. The transports are indicated by the
arrows.
Figure 6-6. Transports in a Multi-Processor Example
Processor 0 Processor 1
Processor 2
Shared memory-based
transports
HPI-based
transports
DMA-based
transports
Transport
array
Transport
array
Transport
array
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