[Bug] EV3 Motor Detection is incomplete

[laurensvalk]

^{Originally posted by @KhuongAnNguyen January 6, 2026}

Hello. I am using the nightly build ev3-firmware-4563 (30-December-2025) on the latest Raspberry Pi Trixie OS.

The program compiled and ran; but sometimes gave random OSError when controlling the medium EV3 servo. For example:

1. OSError: [Errno 1] EPERM: The requested operation is not valid in the current state.
   motor.run_target(speed=1000, target_angle=-150*2, wait=True)
   print(motor.angle())
   wait(1000)
   motor.run_target(speed=1000, target_angle=0, wait=True) # This line triggers the error
2. OSError: [Errno 19] ENODEV: A sensor or motor is not connected to the specified port.
   ev3 = EV3Brick()
   motor = Motor(Port.D) # This line triggers the error
   I double-checked the cable, changed the port. Same issue from time to time.
   If I add "wait(200)" before the motor initialisation, the error seemed to appear less frequently.

What was really strange is that the exact same code ran 50% of the time, but randomly gave up with the above error.

Please help advise me. Thanks.

[laurensvalk]

Thank you for trying our new EV3 version early!

Automatic motor detection still needs some work, so this isn't entirely unexpected.

In this case, ENODEV means that it did not see the device when initializing it, whereas EPERM happens when it no longer sees it in the middle of an operation (even if it did see it before).