add devicetree overlay for the pcm1862

.gitignore

@@ -44,3 +44,5 @@ src/auracast/server/certs/per_device/
 src/auracast/.env
 src/auracast/server/certs/ca/ca_cert.srl
 src/auracast/server/credentials.json
+pcm1862-i2s.dtbo
+test.wav

src/misc/build_pcm1862_dts.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+DTS=./src/misc/pcm1862-i2s.dts
+DTBO=pcm1862-i2s.dtbo
+OUT=/boot/firmware/overlays
+
+# build
+dtc -@ -I dts -O dtb -o "$DTBO" "$DTS"
+
+# install
+sudo install -m 0644 "$DTBO" "$OUT/$DTBO"
+
+# NOTE: also add 
+# dtparam=i2c_arm=on
+# dtoverlay=pcm1862-i2s
+# to /boot/firmware/config.txt
+
+echo "Built and installed $DTBO to $OUT."
+echo "Now either reboot to load the installed overlay"

src/misc/pcm1862-i2s.dts

@@ -0,0 +1,51 @@
+/dts-v1/;
+/plugin/;
+
+/ {
+    compatible = "brcm,bcm2835";
+
+    /* Enable the I²S controller */
+    fragment@0 {
+        target = <&i2s>;
+        __overlay__ { status = "okay"; };
+    };
+
+    /* PCM1862 on I2C1 at 0x4a */
+    fragment@1 {
+        target = <&i2c1>;
+        __overlay__ {
+            #address-cells = <1>;
+            #size-cells = <0>;
+            pcm1862: adc@4a {
+                compatible = "ti,pcm1862";
+                reg = <0x4a>;
+                #sound-dai-cells = <0>;
+            };
+        };
+    };
+
+    /* Link bcm2835-i2s <-> pcm1862 with simple-audio-card */
+    fragment@2 {
+        target-path = "/";
+        __overlay__ {
+            pcm1862_sound: pcm1862-sound {
+                compatible = "simple-audio-card";
+                simple-audio-card,name = "pcm1862 on i2s";
+                simple-audio-card,format = "i2s";
+                /* Pi is master for BCLK/LRCLK */
+                simple-audio-card,bitclock-master = <&dai_cpu>;
+                simple-audio-card,frame-master    = <&dai_cpu>;
+
+                dai_cpu: simple-audio-card,cpu {
+                    sound-dai = <&i2s>;
+                    dai-tdm-slot-num   = <2>;
+                    dai-tdm-slot-width = <32>;
+                };
+
+                simple-audio-card,codec {
+                    sound-dai = <&pcm1862>;
+                };
+            };
+        };
+    };
+};