# How to use MEMS digital PDMIC on RoadRunner SOM

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

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.

<img src="./mp34dt05.jpg" width="260px">

The MEMS microphone used in this article is the [ST MP34DT05-A](https://www.st.com/resource/en/datasheet/mp34dt05-a.pdf).
An evalution kit called [STEVAL-MIC001V1](https://www.st.com/en/evaluation-tools/steval-mic001v1.html) is available from ST to manage easily this very small components:

<img src="./steval-mic001v1.jpg" width="260px">

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...](/roadrunner_compile_kernel_4_19)) 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

## Links

* [Datasheet ST PDMIC MP34DT05-A](https://www.st.com/resource/en/datasheet/mp34dt05-a.pdf)
* [Microchip SAMA5D27 MCU Datasheet](http://www.microchip.com/wwwproducts/en/ATSAMA5D27)
* [How to use record audio stream with PDMIC](https://www.linux4sam.org/bin/view/Linux4SAM/PDMICAudioRecord)

@include='adv_roadrunner'