#!/bin/bash
# Composite USB gadget for the robot, via configfs: NCM Ethernet (usb0) + ACM serial (ttyGS0).
# Installed as /usr/local/sbin/robot-usb-gadget and run by robot-usb-gadget.service.
#   robot-usb-gadget start | stop
set -euo pipefail

G=/sys/kernel/config/usb_gadget/hermes
HOST_MAC=02:68:65:72:6d:01   # the host's end of the link (locally administered, spells "herm")
DEV_MAC=02:68:65:72:6d:02    # the robot's end (usb0)

stop() {
  [ -d "$G" ] || return 0
  cd "$G"
  echo "" > UDC 2>/dev/null || true
  rm -f configs/c.1/ncm.usb0 configs/c.1/acm.usb0
  rmdir configs/c.1/strings/0x409 configs/c.1 functions/ncm.usb0 functions/acm.usb0 strings/0x409 2>/dev/null || true
  cd /
  rmdir "$G" 2>/dev/null || true
}

start() {
  modprobe libcomposite
  mountpoint -q /sys/kernel/config || mount -t configfs none /sys/kernel/config
  stop
  udc=
  for _ in $(seq 40); do          # dwc2 can take a moment to register after boot
    udc=$(ls /sys/class/udc 2>/dev/null | head -n1 || true)
    [ -n "$udc" ] && break
    sleep 0.5
  done
  [ -n "$udc" ] || { echo "robot-usb-gadget: no UDC (is dtoverlay=dwc2,dr_mode=peripheral set?)" >&2; exit 1; }

  mkdir -p "$G"
  cd "$G"
  echo 0x1d6b > idVendor        # Linux Foundation
  echo 0x0104 > idProduct       # multifunction composite gadget
  echo 0x0100 > bcdDevice
  echo 0x0200 > bcdUSB
  echo 0xEF > bDeviceClass      # composite with interface association descriptors
  echo 0x02 > bDeviceSubClass
  echo 0x01 > bDeviceProtocol
  mkdir -p strings/0x409
  echo "$(awk '/^Serial/ {print $3}' /proc/cpuinfo)" > strings/0x409/serialnumber
  echo "Hermes" > strings/0x409/manufacturer
  echo "Hermes robot" > strings/0x409/product

  mkdir -p configs/c.1/strings/0x409
  echo "NCM + ACM" > configs/c.1/strings/0x409/configuration
  echo 250 > configs/c.1/MaxPower

  mkdir -p functions/ncm.usb0
  echo "$HOST_MAC" > functions/ncm.usb0/host_addr
  echo "$DEV_MAC" > functions/ncm.usb0/dev_addr
  mkdir -p functions/acm.usb0
  ln -s functions/ncm.usb0 configs/c.1/
  ln -s functions/acm.usb0 configs/c.1/

  echo "$udc" > UDC
}

case "${1:-}" in
  start) start ;;
  stop) stop ;;
  *) echo "usage: $0 start|stop" >&2; exit 2 ;;
esac