[Bug] Lego Remote Light not working on latest Prime Hub update

[johnscary-ev3]

Describe the bug
The lights on the Lego Remote do not work correctly after I updated the Prime Hub firmware.
Firmware Version: ('primehub', '4.0.0b3', 'ci-release-88-v4.0.0b3 on 2025-12-05')

The light.on(color) statement does not set the light on or change color now. Also does not blink white for start up.
I am using this test program below which is a combination of two examples from the documentation in latest Pybricks Beta environment.
While the program runs and senses the buttons fine, the remote light either is dark or sometimes turns orange,
In my main application I use the remote light color to inform the user about what "mode" I am using. The mode redefines the use of the buttons to get more functionality. So it is important to me
Thanks.

To reproduce
Steps to reproduce the behavior:

from pybricks.pupdevices import Remote
from pybricks.parameters import Button, Color

def button_to_color(buttons):
    # Return a color depending on the button.
    if Button.LEFT_PLUS in buttons:
        return Color.RED
    if Button.LEFT_MINUS in buttons:
        return Color.GREEN
    if Button.LEFT in buttons:
        return Color.ORANGE
    if Button.RIGHT_PLUS in buttons:
        return Color.BLUE
    if Button.RIGHT_MINUS in buttons:
        return Color.YELLOW
    if Button.RIGHT in buttons:
        return Color.CYAN
    if Button.CENTER in buttons:
        return Color.VIOLET
    # Return no color by default.
    return Color.NONE


try:
    # Connect to the remote.
    print('Try to Connect to Remote')
    # Search for a remote for 10 seconds.
    remote = Remote(timeout=10000)
    print("Connected!")

    while True:
        # Wait until a button is pressed.
        pressed = ()
        while not pressed:
            pressed = remote.buttons.pressed()

        print('button=', pressed)
        # Convert button code to color.
        color = button_to_color(pressed)
        print('color=', color)

        # Set the remote light color.
        remote.light.on(color)

        # Wait until all buttons are released.
        while pressed:
            pressed = remote.buttons.pressed()

except OSError:
    print("Could not find the remote.")

Expected behavior
Remote light should change color and also blink white during initial connection.

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

[BertLindeman]

code.pybricks.com firmware

Can confirm the program to run OK with firmware:
Pybricks MicroPython ci-release-86-v3.6.1 on 2025-03-11; SPIKE Prime Hub with STM32F413VG
After connection the remote goes to Blue, after a keypress to the designated color.

beta.pybricks.com firmware

On firmware Pybricks MicroPython ci-release-88-v4.0.0b3 on 2025-12-05; SPIKE Prime Hub with STM32F413VG
it does not.

Updated the program to set the hub button color and that shows the corrected color on the hub, but not at the remote.
And a 10 ms wait to get the complete sentence from print('Try to Connect to Remote') in the log window.

On connect the remote light goes off.
On keypress left plus left center right minus and the center buttons, the color gets different intensities of red.
Seems only the RED part of the colors is shown.
No GREEN nor BLUE.

Updated program to show the desired color also on the hub

from pybricks.pupdevices import Remote
from pybricks.parameters import Button, Color
from pybricks.tools import wait
from pybricks.hubs import ThisHub

hub = ThisHub()

def button_to_color(buttons):
    # Return a color depending on the button.
    if Button.LEFT_PLUS in buttons:
        return Color.RED
    if Button.LEFT_MINUS in buttons:
        return Color.GREEN
    if Button.LEFT in buttons:
        return Color.ORANGE
    if Button.RIGHT_PLUS in buttons:
        return Color.BLUE
    if Button.RIGHT_MINUS in buttons:
        return Color.YELLOW
    if Button.RIGHT in buttons:
        return Color.CYAN
    if Button.CENTER in buttons:
        return Color.VIOLET
    # Return no color by default.
    return Color.NONE

try:
    # Connect to the remote.
    print('Try to Connect to Remote')
    wait(10)  # wait shortly to get the complete word "Remote" on the log window
    # Search for a remote for 10 seconds.
    remote = Remote(timeout=10000)
    print("Connected! to", remote.name())
    wait(2000)

    while True:
        print("Wait until a button is pressed.")
        pressed = ()
        while not pressed:
            pressed = remote.buttons.pressed()

        print('button=', pressed)
        # Convert button code to color.
        color = button_to_color(pressed)
        print('color=', color)

        # Set the remote light color.
        remote.light.on(color)
        hub.light.on(color)

        # Wait until all buttons are released.
        while pressed:
            pressed = remote.buttons.pressed()

except OSError:
    print("Could not find the remote.")

[johnscary-ev3]

Bert, thanks for verifying this issue and doing the updated program.
I have run your updated program also.
Hopefully this is not a too difficult problem for the firmware guys to fix,

[laurensvalk]

Great catch @johnscary-ev3 and thanks for confirming @BertLindeman.

This did not reproduce locally but I can reproduce it with the CI version.

Since the connection is OK, I suspect the data we are sending isn't packed properly or isn't persistent. This is just the type of thing that can vary between compiler versions. This might have masked the issue on my local build.

We'll look into it!

[laurensvalk]

Couple of notes. Technic Hub is affected too, so it is more likely the common code than the Prime Hub Bluetooth stack specifically.

Since it doesn't reproduce locally, we'll use the CI for debuging: https://github.com/pybricks/pybricks-micropython/tree/issue-2497

This logs the message we write to the remote via USB. Already getting some promising results. The color bytes are different.

Working version:

Try to Connect to Remote
BT Write Char: handle=0x000b size=10 data=0a 00 41 00 04 01 00 00 00 01 
BT Write Char: handle=0x000b size=10 data=0a 00 41 01 04 01 00 00 00 01 
BT Write Char: handle=0x000b size=10 data=0a 00 41 34 01 01 00 00 00 00 
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 00 5e 
Connected! to Handset
Wait until a button is pressed.
button= {Button.LEFT_PLUS}
color= Color.RED
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 fb 00 00 
Wait until a button is pressed.
button= {Button.RIGHT_PLUS}
color= Color.BLUE
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 00 5e 
Wait until a button is pressed.
button= {Button.LEFT_MINUS}
color= Color.GREEN
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 5e 00 
Wait until a button is pressed.
button= {Button.RIGHT_MINUS}
color= Color.YELLOW
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 7f 2e 00 
Wait until a button is pressed.
The program was stopped (SystemExit).

CI version, with bad lights:

Try to Connect to Remote
BT Write Char: handle=0x000b size=10 data=0a 00 41 00 04 01 00 00 00 01 
BT Write Char: handle=0x000b size=10 data=0a 00 41 01 04 01 00 00 00 01 
BT Write Char: handle=0x000b size=10 data=0a 00 41 34 01 01 00 00 00 00 
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 00 00 
Connected! to Handset
Wait until a button is pressed.
button= {Button.LEFT_PLUS}
color= Color.RED
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 fb 00 00 
Wait until a button is pressed.
button= {Button.RIGHT_PLUS}
color= Color.BLUE
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 00 00 
Wait until a button is pressed.
button= {Button.LEFT_MINUS}
color= Color.GREEN
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 00 00 00 
Wait until a button is pressed.
button= {Button.RIGHT_MINUS}
color= Color.YELLOW
BT Write Char: handle=0x000b size=10 data=0a 00 81 34 00 51 01 7f 00 00 
Wait until a button is pressed.
The program was stopped (SystemExit).

[laurensvalk]

A fix is available in pybricks/pybricks-micropython#441.

Thanks again. I might not have caught this one.