Pico W sometimes won't start AP immediately after stopping Station

[anecdata]

CircuitPython version

Adafruit CircuitPython 8.1.0-beta.1-46-gb5a26c7f9 on 2023-04-24; Raspberry Pi Pico W with rp2040

Code/REPL

import time
import wifi
import os
import traceback
import microcontroller
import supervisor

time.sleep(3)

while True:
    try:
        print(f"starting station...", end=" ")
        wifi.radio.start_station()
        while not wifi.radio.connected:
            wifi.radio.connect(os.getenv("WIFI_SSID"), os.getenv("WIFI_PASSWORD"))
            print(f"connected={wifi.radio.connected} {wifi.radio.ipv4_address}")
        print(f"stopping station...")
        wifi.radio.stop_station()  # no delay between stop station stop and start AP
        wifi.radio.start_ap('test', 'lksdfjhksdfjlsdfjgh')
        print(f"ap_active={wifi.radio.ap_active} {wifi.radio.ipv4_address_ap}")
        time.sleep(5)
        microcontroller.reset()
    except Exception as ex:
        print(f"")
        traceback.print_exception(ex, ex, ex.__traceback__)

Behavior

This arose on Discord (https://discord.com/channels/327254708534116352/537365702651150357/1100202386905112576 or discord://discord.com/channels/327254708534116352/537365702651150357/1100202386905112576). About 10% of the time, wifi.radio.start_ap() will fail with RuntimeError: Wifi is in station mode. if it immediately follows wifi.radio.stop_station().

A small time delay, or:

        wifi.radio.stop_station()
        while wifi.radio.connected:
            pass
        wifi.radio.start_ap('test', 'lksdfjhksdfjlsdfjgh')

seems to suffice to let start_ap() succeed consistently.

Is this the solution, or could wifi.radio.stop_station() not return until the station is fully stopped?

Description

No response

Additional information

Station-only loops like:

while True:
    wifi.radio.stop_station()
    wifi.radio.start_station()

or

while True:
    try:
        wifi.radio.stop_station()
        wifi.radio.start_station()
        while not wifi.radio.connected:
            wifi.radio.connect(os.getenv("WIFI_SSID"), os.getenv("WIFI_PASSWORD"))
            print(f"connected={wifi.radio.connected} {wifi.radio.ipv4_address}")
    except Exception as ex:
        traceback.print_exception(ex, ex, ex.__traceback__)

do not exhibit any timing issues. Only when switching from Station to AP.

Addendum: Pico W starts up in Station mode. Even if it never connects to an AP, this can still happen. In that case, it doesn't make sense to check wifi.radio.connected, so a time delay may be the only workaround.

[bill88t]

The delay could be considered a 'necessary' part of stopping STA.
So perhaps it should just be added in the stop_station code.

If you guys agree on that I will go ahead and PR it.

[dhalbert]

That makes sense. If the delay is known, the code can wait. It could also poll some status itself and return quicker if it has stopped, but that may not be possible. It shouldn't poll indefinitely in case the status is never satisfied.

[anecdata]

How about looping this check:

circuitpython/ports/raspberrypi/common-hal/wifi/Radio.c

Line 173 in 827eaeb

if (cyw43_tcpip_link_status(&cyw43_state, CYW43_ITF_STA) != CYW43_LINK_DOWN) {

in wifi.radio.stop_station()? I wonder if the wifi leave AP is needed then.

[bill88t]

Sounds good on paper, but will have to be tested. I will do so.
I will also add a regular timeout so it doesn't get stuck.