Trouble with I2S MEMS microphone breakout

[la_croix]

Hi all,

I'm trying to use this on a raspberry pi, running an image built with yocto (unfortunately, I don't have a choice here). I've been told that the kernel contains i2s support, and I've loaded the modules such that lsmod | grep 'snd' gives:

Code: Select all

snd_bcm2835            32768  0
snd_soc_bcm2835_i2s    16384  0
snd_soc_core          188416  1 snd_soc_bcm2835_i2s
snd_compress           20480  1 snd_soc_core
snd_pcm_dmaengine      16384  1 snd_soc_core
snd_pcm                98304  4 snd_pcm_dmaengine,snd_soc_bcm2835_i2s,snd_bcm2835,snd_soc_core
snd_timer              32768  1 snd_pcm
snd                    69632  5 snd_compress,snd_timer,snd_bcm2835,snd_soc_core,snd_pcm

Alsa is definitely installed, etc, but arecord -l gives: **** List of CAPTURE Hardware Devices **** (i.e. an empty list).

I realise that yocto might be a bit out of scope, but I'm looking to outfit fifty pis with one of these microphones each (hence the need for yocto, as I can use the images with mender to update the pis OTA), and I'd really appreciate some help getting it working.

Thanks in advance!

[adafruit_support_mike]

Unfortunately, yocto images collapse so much system functionality into all-in-one binaries that all we can do is point to what does work and let you look for the corresponding parts in your build.

My guess is that you're missing the middleware that lets your applications use the I2S support in the kernel. It's roughly like a kernel with a TCP/IP stack still needing an ssh daemon to handle network logins. The middleware layer in Raspbian is ALSA, which would be a likely candidate for replacement with some build-specific binary in yocto. Check to see what you have there, and what APIs the existing I2S support provides.

[la_croix]

Hi, thanks for this. ALSA is definitely installed, and usable. Could it be anything else?

[adafruit_support_mike]

What configuration are you using for that?