nrf52840 with low power usage

package main

import (
	"device/nrf"
	"time"

	"tinygo.org/x/bluetooth"
)

var adapter = bluetooth.DefaultAdapter

var (
	serviceUUID = [16]byte{0xa0, 0xb4, 0x00, 0x01, 0x92, 0x6d, 0x4d, 0x61, 0x98, 0xdf, 0x8c, 0x5c, 0x62, 0xee, 0x53, 0xb3}
	charUUID    = [16]byte{0xa0, 0xb4, 0x00, 0x02, 0x92, 0x6d, 0x4d, 0x61, 0x98, 0xdf, 0x8c, 0x5c, 0x62, 0xee, 0x53, 0xb3}
)

func main() {
	nrf.USBD.ENABLE.Set(0)

	must("enable BLE stack", adapter.Enable())
	adv := adapter.DefaultAdvertisement()
	must("config adv", adv.Configure(bluetooth.AdvertisementOptions{
		LocalName: "LED colors",
		Interval:  bluetooth.NewDuration(1 * time.Second),
	}))
	must("start adv", adv.Start())

	var ledColorCharacteristic bluetooth.Characteristic
	must("add service", adapter.AddService(&bluetooth.Service{
		UUID: bluetooth.NewUUID(serviceUUID),
		Characteristics: []bluetooth.CharacteristicConfig{
			{
				Handle: &ledColorCharacteristic,
				UUID:   bluetooth.NewUUID(charUUID),
				Flags:  bluetooth.CharacteristicReadPermission | bluetooth.CharacteristicWritePermission | bluetooth.CharacteristicWriteWithoutResponsePermission,
				WriteEvent: func(client bluetooth.Connection, offset int, value []byte) {
				},
			},
		},
	}))

	select {}
}

func must(action string, err error) {
	if err != nil {
		panic("failed to " + action + ": " + err.Error())
	}
}