1. Yongchang, Kai, Justin, Rama
Audio Group
Yongchang, Kai, Justin, Rama

2. Requirements:
The audio library must facilitate the playback of several “wave” files over the UHF radio.
Audio playback requires the use of an 8kHz interrupt, so the code must be very efficient so as not to monopolize the processor.

3. Background
Format of a “wave” file (note this is a stereo wave file, where we will be using mono files)

4. Design
When a playback command is issued, playback is initialized by enabling the “play sample” function call on an 8kHz interrupt. The “play sample” function puts a byte sized sample onto the DAC each time it is called, until the end of the playback is found.

5. Testing
One major complication discovered during testing is that an unprocessed wave file will not easily be audible by simply pushing each byte onto the DAC. The peak-to-peak range of the samples needs to be increased before the audio playback sounds correct.
A program was written to process a wave file and output the modified samples into an array of bytes.

6. Status
Functionality includes playback of a single, pre-defined array of bytes (independent of the “file ID” sent by the command parser).
Playback of multiple wave files was impossible due to the lack of a file system.

7. Future
Future implementation of the audio library will require the audio initialization function to be modified:
The audio initialization function will need to obtain the correct audio file from the file system (this may include multiple file system calls, due to the 512 byte limit on file transfers)
A playback queue would also be a nice feature, so that the audio initialization would not simply ignore a “play audio” command when it is already playing a file.