How to use MEMS digital PDMIC on RoadRunner SOM

This article illustrates how to enable the PDMIC interface integrated inside the SAMA5D27 and how to use it on Linux

The Pulse Density Modulation Interface Controller (PDMIC) is a PDM interface controller and decoder that support mono PDM format. It integrates a clock generator driving the PDM microphone and embeds filters which decimate the incoming bitstream to obtain most common audio rates.

The MEMS microphone used in this article is the ST MP34DT05-A. An evalution kit called STEVAL-MIC001V1 is available from ST to manage easily this very small components:

Embedded Characteristics

16-bit Resolution
DMA Controller Support
Up to 4 Conversions Stored
PDM Clock Source can be Independent from Core Clock
Register Write Protection

Wirings

Up to 2 mics (left and right) can be wired to the RoadRunner pins:

Signal	Berta D2	MP34DT05-A
	3V	1 - VDD
	3V	2 - LR
PDMIC_CLK	PB27	3 - CLK
PDMIC_DAT	PB26	4 - DOUT
	GND	5 - GND

Regarding the signale LR (Left/Right) doesn't matter if you wire it on 3V3 or on GND the PDMIC interface is mono send the voice just on one channel

Kernel setup

To enable the PDMIC driver launch the kernel menuconfig (read how...) and enable these drivers:

Device Drivers > 
    Sound card support > 
        Advanced Linux Sound Architecture > 
            ALSA for SoC audio support 
                <*>   SoC Audio for the Atmel System-on-Chip
                <*>     Atmel ASoC driver for boards using PDMIC

Device tree bindings

Definition to insert inside the apb section:

pdmic@f8018000 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_pdmic_default>;
        atmel,model = "PDMIC @ RoadRunner";
        atmel,mic-min-freq = <1000000>;
        atmel,mic-max-freq = <3246000>;
        atmel,mic-offset = <0x0>;
        status = "okay";
};

Definition to insert inside the pinctrl@fc038000 section:

pinctrl_pdmic_default: pdmic_default {
    pinmux = <PIN_PB26__PDMIC_DAT>,
        <PIN_PB27__PDMIC_CLK>;
    bias-disable;
};

Using the PDMIC from user space

cat /proc/asound/pcm
00-00: CLASSD PCM atmel-classd-hifi-0 : CLASSD PCM atmel-classd-hifi-0 : playback 1
01-00: PDMIC PCM atmel-pdmic-hifi-0 : PDMIC PCM atmel-pdmic-hifi-0 : capture 1

cat /proc/asound/devices 
  0: [ 0]   : control
 16: [ 0- 0]: digital audio playback
 32: [ 1]   : control
 33:        : timer
 56: [ 1- 0]: digital audio capture

sudo arecord -D hw:1,0 -d 10 -f S16_LE -c1 -r48000 p48000.wav
sudo arecord -D hw:1,0 -d 10 -f cd -c1 -r48000 p48000.wav
sudo arecord -D hw:1,0 -d 10 -f cd -c2 -r48000 p48000.wav

How to use MEMS digital PDMIC on RoadRunner SOM

Wirings

Kernel setup

Device tree bindings

Using the PDMIC from user space

Links

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