#!/bin/bash

# A script to automatically find and reset the FTDI USB-to-Serial converter
# commonly used on SiFive development boards like the P550. This is useful
# when a tool like OpenOCD takes exclusive control and doesn't release the
# ttyUSB devices correctly.

set -e

# --- Configuration ---
# The Vendor and Product ID for the FTDI FT4232H Quad-HS USB-UART/FIFO IC.
# You can verify this for your board by running `lsusb`.
VENDOR_ID="0403"
PRODUCT_ID="6011"

# --- Sanity Checks ---
if [ "$(id -u)" -ne 0 ]; then
  echo "This script must be run as root. Please use 'sudo'." >&2
  exit 1
fi

if ! [ -d /sys/bus/usb/drivers/usb ]; then
    echo "Error: USB drivers not found at /sys/bus/usb/drivers/usb." >&2
    exit 1
fi

# --- Main Logic ---
echo "Searching for USB device with ID ${VENDOR_ID}:${PRODUCT_ID}..."

FOUND_BUS_ID=""
for dir in /sys/bus/usb/devices/*; do
  if [ -f "${dir}/idVendor" ] && [ -f "${dir}/idProduct" ]; then
    if [ "$(cat "${dir}/idVendor")" == "${VENDOR_ID}" ] && [ "$(cat "${dir}/idProduct")" == "${PRODUCT_ID}" ]; then
      FOUND_BUS_ID=$(basename "${dir}")
      echo "Found SiFive board on USB bus ID: ${FOUND_BUS_ID}"
      break
    fi
  fi
done

if [ -z "${FOUND_BUS_ID}" ]; then
  echo "Error: Could not find a connected SiFive board (FTDI ${VENDOR_ID}:${PRODUCT_ID})." >&2
  echo "Please ensure the board is connected." >&2
  exit 1
fi

echo "Resetting USB device..."

# Unbind the device from the kernel
echo " - Unbinding driver from ${FOUND_BUS_ID}..."
echo -n "${FOUND_BUS_ID}" > /sys/bus/usb/drivers/usb/unbind

# Give it a moment to process
sleep 1

# Bind the device, prompting the kernel to re-attach the driver
echo " - Binding driver to ${FOUND_BUS_ID}..."
echo -n "${FOUND_BUS_ID}" > /sys/bus/usb/drivers/usb/bind

echo "Done. The /dev/ttyUSB* devices should reappear shortly."