Technicalities » DAPM http://www.sirena.org.uk/log Just another random blog Fri, 16 Jul 2010 17:24:50 +0000 en hourly 1 http://wordpress.org/?v=3.0 ASoC changes in 2.6.30 http://www.sirena.org.uk/log/2009/06/10/asoc-changes-in-2630/ http://www.sirena.org.uk/log/2009/06/10/asoc-changes-in-2630/#comments Wed, 10 Jun 2009 08:31:00 +0000 Mark Brown http://www.sirena.org.uk/log/?p=174 Linux 2.6.30 was released today. This has been a fairly quiet release from the ASoC point of view with no substantial API changes for drivers but there’s a few new interfaces which people may find helpful. Highlights include:

  • A simple wrapper for the standard ALSA jack detection interface. This helps makes jacks a bit easier to use in a multi-component system, providing a framework for using multiple jack detection methods on a single jack (eg, for both headphone and microphone) and automatic integration with DAPM, allowing output paths to be powered up only when a jack is present. See sound/soc/soc-jack.c.
  • A new SND_SOC_DAPM_PIN_SWITCH helper for machines exposing control of DAPM pins to user applications.
  • More conversion of ASoC CODEC drivers to use the new device model integrated driver registration methods.
  • TI DaVinci support now works in mainline, no out of tree patches are required for the DMA code.

plus a selection of new drivers and enhancements to existing drivers..

]]> http://www.sirena.org.uk/log/2009/06/10/asoc-changes-in-2630/feed/ 0 DAPM power sequence optimisation http://www.sirena.org.uk/log/2009/06/08/dapm-power-sequence-optimisation/ http://www.sirena.org.uk/log/2009/06/08/dapm-power-sequence-optimisation/#comments Mon, 08 Jun 2009 18:08:26 +0000 Mark Brown http://www.sirena.org.uk/log/?p=178 I recently implemented some enhancements to DAPM, the part of ASoC which minimizes the power consumption of the embedded audio subsystem by keeping any unused components powered off while avoiding audible artifacts as the power changes. Prior to these changes DAPM used to change the power for each component with an individual register write which with many systems would result in a lot of repeated writes to the same register. This can get noticeable on slow or heavily contended buses, especially around resume. With these changes DAPM will try to minimize the number of register writes it does while still trying to avoid audio artifacts. These changes are currently available from the dapm branch of my ASoC git repository and should make their way into 2.6.32. Once they are merged the dapm branch is likely to be removed.

As with any substantial change in the power sequencing there is a risk that there may have been some performance regressions on some systems – my biggest concern is that some thing were being helped by the delays introduced by the repeated register writes and may require special handling to fix. My hope is that this won’t happen if anything it should fix some problems by ensuring that both left and right channels of stereo paths get powered up together without wide testing that’s hard to guarantee. Any testing that you can do on your systems would be greatly appreciated.

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