[Bug] [EV3] NXT color sensor is not recognized or replug on all ports, but the sensor is activate on a re-boot

[BertLindeman]

Describe the bug
Plug an NXT color sensor into port S1 and replug into S2 etc.
The sensor light is ON on Port.S1 and Port.S4 but not on ports S2 and S3.
Keep the sensor in a port where the light does NOT come on.
Then power off and on the hub.
Now the sensor is activated.

I assume the light-on means the sensor is correctly recognized.

To reproduce
Steps to reproduce the behavior:

1. Get an EV3 with V4.0.0.b7 firmware and power-on
2. Plug the NXT color sensor successively in Ports S1-S2-S3-S4
3. Remember on which port the light stayed OFF. Keep the sensor in that port.
4. Power-off the hub and power-on again
5. See that now the sensor is activated and the light goes on.

Expected behavior
What did you expect to happen instead?
The sensor should be activated either in none of the ports or in all.

Screenshots
There is a saying that a picture is worth a 1000 words. Screenshots really help to identify and solve problems.

extra info

1. The EV3 on firmware local-build-v4.0.0b6-11-gba4b03996-dirty on 2026-02-26
   did similar, but on different port.
   Sensorlight stayed OFF on Port.S3

2. Tried the same with an NXT Light sensor, EV3 color sensor and those did not suffer this problem.

[laurensvalk]

I can't seem to be able to reproduce this.

Here is a firmware version with debug info for EV3 detection enabled. You should get output such as:

Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.

In cases where the light does not come on, what do you see?

firmware.zip

[BertLindeman]

With your debug firmware all ports activate the NXT ColorSensor and report like this:

Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan

So can not recreate the problem on this firmware.

(My C knowledge is zero, so will not try the crc fix)

[BertLindeman]

Update:
Did many more tests and then the NXT color sensor did not light up a few times.
But the log did show the same data. 3 plug in / out (On the sensor side cable off/on) shows:

Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.
Color Sensor disconnected.
Start device scan
Device kind detected: 97
Initializing NXT Color Sensor.
Finished initializing NXT Color Sensor.

First plugin - no light
second plugin - light
third plugin - no light.

It is not a cable issue, as the color sensor is fixed to the hub and if the led does not come on, I do a reboot without touching the cable. After reboot the light gets on.