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4.4.1 Example: Changing output format

You may wish to customize the digital output format e.g. for a CODEC that expects

sample data left justiﬁed with respect to the word clock.

To do this you need to alter the main audio driver loop in

audio.xc

. After the

alteration you need to re-test the functionality. The XMOS Timing Analyzer can

help guarantee that your changes do not break the timing requirement of this core.

4.4.2 Example: Adding DSP to output stream

To add some DSP requires an extra core of computation, so some existing func-

tionality needs to be removed (e.g. S/PDIF). Follow these steps to update the

code:

1. Remove some functionality using the deﬁnes in §5.1.

Add another core to do the DSP. This core will probably have three XC channels:

one channel to receive samples from decoupler core and another to output to

the audio driver—this way the core ‘intercepts’ audio data on its way to the

audio driver; the third channel can receive control commands from Endpoint 0.

Implement the DSP on this core. This needs to be synchronous (i.e. for every

sample received from the decoupler, a sample needs to be outputted to the

audio driver).

Update the Endpoint 0 code to accept custom requests to the audio class

interface to control the DSP. It can then forward the changes onto the DSP core.

5. Update host drivers to use these custom requests.

REV 6.1

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