enable LED blink

buildroot-2021.05/board/milkv/duo/overlay/etc/init.d/S99user

@@ -15,9 +15,14 @@ case "$1" in
 
         echo "Starting app..."
 
+        if [ -f $SYSTEMPATH/blink.sh ]; then
+                . $SYSTEMPATH/blink.sh &
+        fi
+
 	if [ -f $SYSTEMPATH/rndis.sh ]; then
                 . $SYSTEMPATH/rndis.sh &
         fi
+
         if [ -f $USERDATAPATH/auto.sh ]; then
                 usleep 30000
                 . $USERDATAPATH/auto.sh &

milkv/overlay/mnt/system/blink.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+LED_GPIO=/sys/class/gpio/gpio440
+
+if test -d $LED_GPIO; then
+    echo "GPIO440 already exported"
+else
+    echo 440 > /sys/class/gpio/export
+fi
+
+echo out > $LED_GPIO/direction
+
+while true; do
+    echo 0 > $LED_GPIO/value
+    sleep 0.5
+    echo 1 > $LED_GPIO/value
+    sleep 0.5
+done
+