commaai/openpilot · error · RuntimeError

could not disable USB runtime PM: {control}

Error message

could not disable USB runtime PM: {control}

What it means

RuntimeError from disable_runtime_pm() in the chestnut flasher: it writes 'on' to the device's sysfs power/control file but a read-back returns something other than 'on', so runtime power management is still active and could suspend the device mid-flash. The flasher refuses to continue with nondeterministic USB power state.

Source

Thrown at openpilot/system/hardware/chestnut/flash.py:87

      pass
  if len(found) > 1:
    raise RuntimeError(f"expected one chestnut, found {len(found)}")
  return found[0] if found else (None, None, None)


def in_rom_bootloader(vid_pid, product):
  # the ROM bootloader reports the config page strings, or its own when the config page is lost
  return vid_pid in ROM_VID_PIDS or product == ROM_PRODUCT or (product or "").startswith("AS2462")


def disable_runtime_pm(path):
  control = os.path.join(path, "power/control")
  if not os.path.exists(control):
    return
  with open(control, "w") as f:
    f.write("on\n")
  if open(control).read().strip() != "on":
    raise RuntimeError(f"could not disable USB runtime PM: {control}")
  delay = os.path.join(path, "power/autosuspend_delay_ms")
  if os.path.exists(delay):
    with open(delay, "w") as f:
      f.write("-1\n")


def unbind_drivers(path):
  for interface in glob.glob(path + ":*"):
    driver = interface + "/driver"
    if os.path.islink(driver):
      with open(os.path.realpath(driver) + "/unbind", "w") as f:
        f.write(os.path.basename(interface))


def open_device(path):
  bus, dev = int(open(path + "/busnum").read()), int(open(path + "/devnum").read())
  return os.open(f"/dev/bus/usb/{bus:03d}/{dev:03d}", os.O_RDWR)

View on GitHub (pinned to 516ec1e682)

Solutions

1. Run the flasher as root (sudo) so sysfs writes take effect
2. Check dmesg and /sys/<dev>/power/control manually: echo on, then cat to see whether it sticks
3. If in a container, run with /sys mounted rw or flash from the host

Example fix

# before
python3 flash.py   # as normal user

# after
sudo python3 flash.py

import os

def runtime_pm_writable(sysfs_path: str) -> bool:
    control = os.path.join(sysfs_path, 'power', 'control')
    if not os.path.exists(control):
        return True  # nothing to disable
    return os.access(control, os.W_OK)

try:
    disable_runtime_pm(sysfs_path)
except RuntimeError as e:
    if 'runtime PM' in str(e):
        raise RuntimeError('rerun the flasher as root so sysfs power/control writes take effect') from e
    raise

When it happens

Trigger: Running the flasher without root (sysfs power files are root-writable, so the write silently fails or is ignored), an unusual kernel/driver that ignores power/control writes, or a read-only sysfs mount.

Common situations: Invoking the flash tool as a normal user instead of sudo, containers without writable /sys, or a kernel where the USB driver does not honor runtime PM control for that interface.

Related errors

• flash did not converge within {FLASH_BUDGET:g}s
• expected one chestnut, found {len(found)}
• Unhandled sparse chunk type
• Raw hash mismatch '{raw_hash.hexdigest().lower()}'
• Uncompressed size mismatch

AI-assisted analysis of commaai/openpilot@516ec1e682 (2026-08-15). Data as JSON: /api/errors/940cda21d8d02f5b. Report an issue: GitHub.