[RP2040] `maxlen` parameter in `pulseio.PulseIn` is not respected

[eigenein]

Related issues: #4659 #4660

Firmware

Adafruit CircuitPython 6.2.0 on 2021-04-05; Raspberry Pi Pico with rp2040

code.py

Note: GP16 and GP17 are directly connected with a wire.

from board import GP16, GP17
from digitalio import DigitalInOut, Direction
from pulseio import PulseIn
from time import sleep

trigger = DigitalInOut(GP16)
trigger.direction = Direction.OUTPUT
trigger.value = False

echo = PulseIn(GP17, maxlen=3, idle_state=False)


def trigger_pulse(seconds: float):
    print(f"Triggering ~{seconds:.6}s pulse…")
    trigger.value = True
    sleep(seconds)
    trigger.value = False
    print("Done:", [echo[i] for i in range(len(echo))])


sleep(1.0)  # giving myself enough time to connect to the serial
for i in range(10):
    trigger_pulse(0.001000)

Output

The documentation says:

When there is no more room (len() == maxlen) the oldest pulse length is removed to make room.

But the list keeps growing despite the maxlen=3:

code.py output:
Triggering ~0.001s pulse…
Done: [816]
Triggering ~0.001s pulse…
Done: [816, 183]
Triggering ~0.001s pulse…
Done: [816, 183, 237]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183, 237]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183, 237, 816]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183, 237, 816, 183]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183, 237, 816, 183, 237]
Triggering ~0.001s pulse…
Done: [816, 183, 237, 816, 183, 237, 816, 183, 237, 816]

Code done running.