Instructions for Enabling DMIC support in Dragonboard410c

This document provides instructions for enabling DMIC support in Dragonboard410c.

Table of Contents

1) DMIC (Digital MIC) in Dragonboard410c

Dragonboard410c has one DMIC port which can be used to connect external Digital Microphone (two can be connected as a multiplex). APQ8016 provides the CLK and DATA signals while PM8916 provides the MIC_BIAS. On the Dragonboard410c DATA and CLK signals are exposed on the LS expansion header (J8) while MIC_BIAS is available at the Analog Expansion header (J7). Also, CLK and DATA signals are multiplexed to the UART0 TxD and RxD signals at Pin 4 and 6 on J8.

2) Hardware Required

  • Dragonboard410c
  • Arrow Audio Mezzanine board

3) Modifying Device Tree

Since, UART signals are multiplexed to DMIC CLK and DATA signals on pads, we need to disable UART0 and enable DMIC in order to use it.

Apply the following diff to arch/arm64/boot/dts/qcom/apq8016-sbc.dtsi

diff --git a/arch/arm64/boot/dts/qcom/apq8016-sbc.dtsi b/arch/arm64/boot/dts/qcom/apq8016-sbc.dtsi
index 5d0d5a3..061f5f3 100644
--- a/arch/arm64/boot/dts/qcom/apq8016-sbc.dtsi
+++ b/arch/arm64/boot/dts/qcom/apq8016-sbc.dtsi
@@ -42,7 +42,7 @@

                serial@78af000 {
                        label = "LS-UART0";
-                       status = "okay";
+                       status = "disabled";
                        pinctrl-names = "default", "sleep";
                        pinctrl-0 = <&blsp1_uart1_default>;
                        pinctrl-1 = <&blsp1_uart1_sleep>;
@@ -281,13 +281,17 @@
                         reg-names = "mic-iomux", "spkr-iomux";

                         status = "okay";
-                        pinctrl-0 = <&cdc_pdm_lines_act &ext_sec_tlmm_lines_act &ext_mclk_tlmm_lines_act>;
-                        pinctrl-1 = <&cdc_pdm_lines_sus &ext_sec_tlmm_lines_sus &ext_mclk_tlmm_lines_sus>;
+                        pinctrl-0 = <&cdc_pdm_lines_act &ext_sec_tlmm_lines_act &ext_mclk_tlmm_lines_act &cdc_dmic_lines_act>;
+                        pinctrl-1 = <&cdc_pdm_lines_sus &ext_sec_tlmm_lines_sus &ext_mclk_tlmm_lines_sus &cdc_dmic_lines_sus>;
                         pinctrl-names = "default", "sleep";
                         qcom,model = "DB410c";
                         qcom,audio-routing =
                                 "AMIC2", "MIC BIAS Internal2",
-                                "AMIC3", "MIC BIAS External1";
+                                "AMIC3", "MIC BIAS External1",
+                                "DMIC1", "MIC BIAS Internal1",
+                                "DMIC1", "Digital Mic1",
+                                "DMIC2", "MIC BIAS Internal1",
+                                "DMIC2", "Digital Mic2";
                        external-dai-link@0 {
                                link-name = "ADV7533";
                                cpu { /* QUAT */
@@ -609,4 +613,4 @@

4) Building Device Tree

Build the device tree with above mentioned changes.

$ export ARCH=arm64
$ export CROSS_COMPILE=<path to your GCC cross compiler>/aarch64-linux-gnu-
$ make defconfig distro.config
$ make -j$(nproc) dtbs

Now, prepare the boot image.

$ git clone git://
$ ./skales/dtbTool -o dt.img -s 2048 arch/arm64/boot/dts/qcom/
$ wget* -O initrd.img
$ wget* -O vmlinuz
$ ./skales/mkbootimg --kernel vmlinuz \
                   --ramdisk initrd.img \
                   --output boot-db410c.img \
                   --dt dt.img \
                   --pagesize 2048 \
                   --base 0x80000000 \
                   --cmdline "root=/dev/disk/by-partlabel/rootfs rw rootwait console=ttyMSM0,115200n8"

5) Flashing boot and roofs image

Boot Dragonboard410c into fastboot mode by following the instructions.

  1. Download latest rootfs image from here.
  2. Flash boot and rootfs images onto Dragonboard410c
$ sudo fastboot flash boot boot-db410c.img
$ sudo fastboot flash rootfs linaro-<DEBIANRELEASE>-alip-<BUIILD>.img

Note: Replace < DEBIANRELEASE > and < BUILD > according to the downloaded rootfs image.

6) Testing DMIC

Note: Make sure you have soldered Male headers on the Analog Expansion header (J7) on Dragonboard410c before connecting the Audio Mezzanine.

  • Stack Audio Mezzanine on top of Dragonboard410c
  • Boot Dragonboard410c with the above mentioned custom Boot image and pre-built RFS image.

For testing the audio capture functionality using DMIC, follow the below commands on Dragonboard:

First setup mux to use DMIC.

$ amixer cset iface=MIXER,name='DEC1 MUX' 'DMIC1'
$ amixer cset iface=MIXER,name='CIC1 MUX' 'DMIC'

Now, record audio using DMIC present in Audio Mezzanine.

$ arecord -D plughw:0,2 -r 48000 -f S16_LE /tmp/f-48000.wav

After recording audio, mux can be reset using the following command.

$ amixer cset iface=MIXER,name='DEC1 MUX' 'ZERO'
$ amixer cset iface=MIXER,name='CIC1 MUX' 'ZERO'