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 eVC - AC97 mic-to-speaker app (direct codec ctrl)
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1519 Posts

Posted - 11 Nov 2003 :  17:46:52  Show Profile  Email Poster

AudioLoop illustrates how to use IOCTLs to control the routing functions of the AC97 audio codec.

This particular example loops the microphone inputs of the BitsyX (and similar products) out to the speakers.

(Although this application does not involve an AM radio, it may remind U.S. customers of a product sold in the late 1970s called Mr. Microphone. )

The Codec Archtecture and Datasheet
Interested parties can download the datasheet for the CS4202 codec (PDF 1.2MB) to see how this app works. The analog multiplexers are organized as follows:

Source: Crystal CS4202 codec data sheet, May 2002 (PDF)

Audio signal routing is described in section 2.4 The codec registers are described in chapter 4.

Key APIs Used



Lines of Code: 275

Source Download
Rev 1, 10-nov-2003 (ZIP 36kB).

Related topics: Audio topic index, Show_AC97_Registers app

Edited by akidder 16-Feb-2004: Add image of audio mixer.
Edited by akidder 15-Jul-2004: Add link to Show_AC97_Registers application


1519 Posts

Posted - 18 Feb 2004 :  11:20:21  Show Profile  Email Poster
We've added a picture of the audio codec signal routing.
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