ARMv5 Olinuxino board - problems with ALSA audio

[TrevorPage]

Firstly, apologies if this is not the most appropriate section (or not the most appropriate forum whatsoever) to post this. Please let me know if there's another forum or mailing list where I might get more response to this.

My situation is that I am using an Olinuxino Maxi (i.MX233 processor) with the latest Arch Linux ARM SD card image specifically for this board. It is running a VOIP application that I have developed for it, using the Linphone library.

With the latest ALARM build working on the board, I then switched to the mainline kernel (3.12+) by installing the package linux-armv5, which replaced default linux-olinuxino kernel (in accordance with a note on the download page). By doing this, I then have support for the onboard i.MX233 audio, which I believe has only recently gone into the mainline kernel.

Although audio works and I can make Linphone calls and record / play audio, a significant problem is that there is a periodic clicking noise on audio sampled from the line input on the board, except for the first time the line input is used since boot. To clarify what I mean, if I reboot the board and then use arecord to make three recordings, the first recording is clean and all subsequent recordings contain the clicking noise. Similarly, if I reboot and then make Linphone VOIP calls, only the first call is 'clean'; for subsequent calls, transmitted audio has the noise (although it manifests itself more as a nasty 'chopping' noise over the VOIP calls).

For example:
- Reboot the board.
- Use arecord to record audio to test1.wav.
- Use arecord to record audio to test2.wav.
- aplay test1.wav. The audio is clean.
- aplay test2.wav. The audio is noisy with fast cyclic clicking.
- Any subsequent recordings are noisy. The only way to create another clean recording is to reboot.

I have tried all sorts of experimentation with alsamixer settings without success. Attempting to make the audio input go 'clean' again by using alsactl to reset and initialise the audio simply has no effect. Once the first 'clean' arecord or Linphone call has finished since boot, the line-in goes 'dirty' and nothing I can do will revert it.

Any ideas please?