[alsa-devel] About joining codecs together

Mike Looijmans mike.looijmans at topic.nl
Thu Sep 6 08:43:32 CEST 2012

I have multiple codecs (TLV320AIC3256) connected to the McASP of an OMAP L138. I've adapted the drivers a bit so they work with my 2.6.37 kernel and the custom board (similar to a DA850).

Currently, I can only use one codec at a time. The mcasp is set up in the board config, and there it determines which AXR lines are active. Each codec is connected to another line. They run on the same clock lines.

- How can I forward information from the codec to the mcasp driver, to inform which AXR channel to enable? There seems to be no information exchange between them. When codec 1 is running, the mcasp driver must record from AXR1, and when codec2 is running, AXR2 and so on.

What I ultimately want to do is use two (or more) codecs for multichannel recording, so that I can use two codecs for a 4-channel recording. For the McASP side, this would simply mean enabling both AXR inputs (DAVINCI_MCASP_PDIR_REG) and then starting both codecs.

- How does this work in user space? There are two codecs, which are to be configured independently, but there will be only one audio stream coming out.

I was thinking to create a sort of "multiswitch", a codec that by itself doesn't really do anything, but presents itself as a single codec with lots of channels. The actual commands will be delivered to the appropriate "real" codecs, so that you can record from the "switch", which then in turn enables two codecs and sets up the DAI to record both streams. Would that be possible at all? What are the alternatives?

Met vriendelijke groet / kind regards,

Mike Looijmans

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E-mail: mike.looijmans at topic.nl
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