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Playback Features

Playback by File Offset and Length

This feature provides two benefits:

• an application can play from a particular location within a file by providing an offset, in bytes, from the beginning of the file

• a user can specify how long the file should play, so it doesn’t have to play to the end

When only part of a file is requested to be played, only the requested bytes are cached (not the entire file) on both the 8260 chip and the DSP. Because the Offset and Length are in bytes, and because they represent bytes in a file, the application is responsible for managing the different encoding formats, and for how bytes should represent time.

Handling Inconsistent File Sizes

If the Length plus the Offset is greater then the actual file size, the file plays until the end. If the Offset is greater then the actual file size, a File Open error occurs.

Dynamic File Management

Using NFS, recorded voice files are handled dynamically through a Least Recently Used algorithm. Voice files are downloaded to the card’s memory one at a time, and as the memory on the card is consumed, a Least Recently Used (LRU) algorithm keeps track of the order in which the files are played. When the memory is completely consumed, the following takes place:

1. The LRU algorithm identifies the Least Recently Used File ID.

2. This File ID is then deleted.

3. The memory blocks are freed for further use.

The DSP Series 2 card also has one hour of cache per DSP chip. The purpose of this cache is to increase performance for frequently used messages, not to increase storage capacity.

When the host application sends an instruction to play a specific file on a specific DSP chip, the DSP chip then:

1. Checks its one hour cache for the announcement file.

2. Checks the main board’s three hour cache for the announcement file.

Checks the Network File System server (if used) for the announcement file.

Digital Signal Processor