diff --git a/py/tarpn/bbd/firmware_update.py b/py/tarpn/bbd/firmware_update.py
index bf70618..4f63a0a 100644
--- a/py/tarpn/bbd/firmware_update.py
+++ b/py/tarpn/bbd/firmware_update.py
@@ -64,14 +64,17 @@ def start_agent_process():
     assert check_agent_process(), "Started agent program, but not showing RUNNING"
 
 
-def ensure_serial_port_free():
-    p = subprocess.run(shlex.split("lsof /dev/ttyS0"), stdout=subprocess.PIPE)
+def ensure_serial_port_free(device: str):
+    if not os.path.exists(device):
+        assert False, f"No such device {device}"
+    p = subprocess.run(shlex.split(f"lsof {device}"), stdout=subprocess.PIPE)
     if p.returncode == 1:
+        # lsof will return code 1 if nothing is using the device
         return
     else:
         lines = p.stdout.decode("ascii").split("\n")
         cols = re.split("\s+", lines[1])
-        assert False, f"Process {cols[0]} (pid {cols[1]}) is using the serial port"
+        assert False, f"Process {cols[0]} (pid {cols[1]}) is using the serial port {device}"
 
 
 def reset_atmega(gpio: int) -> True:
@@ -89,29 +92,32 @@ def reset_atmega(gpio: int) -> True:
     GPIO.output(gpio, GPIO.HIGH)
 
 
-def upload_firmware():
+def upload_firmware(device: str):
     path = firmware_file()
-    p = subprocess.run(shlex.split(f"avrdude -v -p atmega328p -c arduino -b 38400 -D -P /dev/ttyS0 -U flash:w:{path}:i"))
+    p = subprocess.run(shlex.split(f"avrdude -v -p atmega328p -c arduino -b 38400 -D -P {device} -U flash:w:{path}:i"))
     assert p.returncode == 0, "Firmware upload failed!"
 
 
 def main():
     parser = argparse.ArgumentParser(description="Firmware updater for TARPN BBD")
-    parser.add_argument("--gpio", type=int, default=7, help="Override the default GPIO used for Atmega reset (7).")
+    parser.add_argument("--gpio", type=int, default=7,
+                        help="The GPIO pin used to reset the ATmega microcontroller. Defaults to pin 7 (GPIO 4).")
+    parser.add_argument("--device", type=str, default="/dev/ttyS0",
+                        help="The serial device that the BBD is connected to. Defaults to hardware UART /dev/ttyS0")
     parser.add_argument("--dry-run", action="store_true", help="Perform a dry-run of the firmware update")
-    parser.add_argument("--reset-only", action="store_true", help="Only reset the atemga, do not update the firmware")
+    parser.add_argument("--reset-only", action="store_true", help="Only reset the ATmega, do not update the firmware")
 
     args = parser.parse_args()
     if args.reset_only:
-        check(partial(reset_atmega, args.gpio), "atmega is reset", skip=args.dry_run)
+        check(partial(reset_atmega, args.gpio), "ATmega is reset", skip=args.dry_run)
         exit(0)
 
     check(ensure_firmware_file, "firmware is present")
     check(ensure_supervisor, "supervisor is installed") 
     check(stop_agent_process, "agent is not running", allow_fail=True)
-    check(ensure_serial_port_free, "serial port is unused") 
-    check(partial(reset_atmega, args.gpio), "atmega is reset", skip=args.dry_run)
-    check(upload_firmware, "firmware is uploaded", skip=args.dry_run)
+    check(partial(ensure_serial_port_free, args.device), f"serial port {args.device} is unused")
+    check(partial(reset_atmega, args.gpio), "ATmega is reset", skip=args.dry_run)
+    check(partial(upload_firmware, args.device), "firmware is uploaded", skip=args.dry_run)
     check(start_agent_process, "agent is running")