[Bug] Prime Hub broadcast does not work properly if broadcasting too fast

[laurensvalk]

here is my code:

from pybricks.hubs import PrimeHub
from pybricks.pupdevices import Motor, ColorSensor, UltrasonicSensor, ForceSensor
from pybricks.parameters import Button, Color, Direction, Port, Side, Stop
from pybricks.robotics import DriveBase
from pybricks.tools import wait, StopWatch

hub = PrimeHub(broadcast_channel=10)
mode = 0

while (True):
    print('') # the problem
    if (mode == 0):
        direction = 0
        x = 0
        y = 0
        t = hub.imu.tilt()
        if (t[1] > 30):
            y = 1
        elif (t[1] < -30):
            y = -1
        
        if (t[0] > 30):
            x = -1
        if (t[0] < -30):
            x = 1
        hub.ble.broadcast(x, y)

this code is for broadcasting signal to the other hub, but I realized that I can only broadcast this consistently if I connect this to my computer, and print something. otherwise, it would only send every two seconds, for about 5 pulses instead of sending signal all the time. Is there a way to make the robot work more independently? I don't want to always connect this hub to my computer when I run it.

Originally posted by @Potato-eater in #1149

[laurensvalk]

On Prime Hub, we could add a wait(max(0, 10 - (time_now - time_last_broadcast) before broadcasting. This way it introduces delays only in tight loops.

Having this method (a)wait would make it consistent with the other hubs, which is probably a good thing.

[laurensvalk]

The PT_THREAD for this is already set up in the right form. It probably just needs a short wait in it (but only if recently called, as per above).

[laurensvalk]

I can reproduce this problem consistently as follows:

SPIKE Prime receiver with this script, running disconnected from PC:

from pybricks.hubs import ThisHub
from pybricks.parameters import Color
from pybricks.tools import wait, StopWatch

hub = ThisHub(observe_channels=[12])

watch = StopWatch()

while True:
    data = hub.ble.observe(12)
    if data:
        hub.display.number(data)
    wait(10)

SPIKE Essential sender:

from pybricks.hubs import EssentialHub
from pybricks.pupdevices import ColorLightMatrix
from pybricks.parameters import Color, Port
from pybricks.tools import wait, StopWatch

hub = EssentialHub(broadcast_channel=12)

watch = StopWatch()

while True:
    for i in range(100):
        data = i
        color = Color.RED if i % 2 else Color.GREEN
        hub.ble.broadcast(data)
        print(watch.time())
        hub.light.on(color)
        # wait(10)   <--- Needed to make it work when disconnected from PC

[laurensvalk]

This fix had to be undone via pybricks/pybricks-micropython@da7565e because it wasn't the right fix.

So we should also revert pybricks/pybricks-micropython@cf73380 which can now hang the hub. We should probably implement the todo/fixme mentioned in there to await setting the broadcast data instead of waiting 10 ms anyway.

[dlech]

It should also be possible to use the BTStack timer API instead, if needed.