feat: Add script to reset SiFive P550 USB TTYs

This script automates the process of unbinding and binding the FTDI
USB driver, which is useful for restoring serial console access after
running tools like OpenOCD.

reset_sifive_usb.sh

@@ -0,0 +1,60 @@
+#!/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."