Debugging I2S microphone input issue

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Debugging I2S microphone input issue

Postby RobMeades » Mon Jan 29, 2018 4:40 pm

I am trying, and failing, to connect an I2S microphone (Invensense ICS43432) to my Raspberry Pi (B+) and would like to ask for advice on how to go about debugging such an audio recording problem.

I have adapted the instructions for Raspbian to do this under Arch (v4.9.78). I have built and loaded the ics43432.c module [unedited] from Linux source 4.9.78 (no errors at boot in dmesg aside from kernel taint) then configured a sound card using DTC. The lsmod output seems correct:

$this->bbcode_second_pass_code('', 'snd_soc_bcm2835_i2s 6745 2
snd_soc_simple_card 5509 0
snd_soc_simple_card_utils 4423 1 snd_soc_simple_card
bcm2835_gpiomem 3515 0
bcm2835_rng 2679 0
rng_core 7676 1 bcm2835_rng
uio_pdrv_genirq 3456 0
uio 9072 1 uio_pdrv_genirq
fixed 2921 0
sch_fq_codel 9358 2
snd_bcm2835 21570 0
snd_soc_ics43432 2050 1
snd_soc_core 157891 4 snd_soc_ics43432,snd_soc_simple_card_utils,snd_soc_bcm2835_i2s,snd_soc_simple_card
snd_compress 9500 1 snd_soc_core
snd_pcm_dmaengine 4847 1 snd_soc_core
snd_pcm 87826 4 snd_pcm_dmaengine,snd_soc_bcm2835_i2s,snd_bcm2835,snd_soc_core
snd_timer 21638 1 snd_pcm
snd 60574 5 snd_compress,snd_timer,snd_bcm2835,snd_soc_core,snd_pcm
ip_tables 12235 0
x_tables 17324 1 ip_tables
ipv6 387315 48
')
arecord -l shows that a mems microphone "soundcard" is present and I have boosted the volume on that input by 30 dB using alsamixer. The full blow-by-blow account of the entire setup process can be found here but, in theory at least, it should all be working.

Using a logic analyser I have verified that the I2S interface is running and that my microphone is returning valid looking left-channel data on pin 38 of the Raspberry Pi header.

However, all my attempts to record from the microphone produce a file where all data bytes are zero, so something is plainly not right. Can anyone suggest how I go about debugging where my nice valid-looking audio input data is going?
RobMeades
 
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Joined: Sat May 17, 2014 3:35 pm

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