CIRCUITPY spontaneously disconnects after mounting sd card and wifi network scan

[phesterman]

CircuitPython version and board name

Adafruit CircuitPython 10.0.1 on 2025-10-09; Raspberry Pi Pico W with rp2040

Code/REPL

# code.py

import mount_sdcard, basic_wifi_test

******************************************

# mount_sdcard.py
# 08/10/2025

import board, busio, sdcardio, storage, sys

sck = board.GP18
si = board.GP19
so = board.GP16
cs = board.GP17

#  SPI setup for SD card
spi = busio.SPI(sck, si, so)
sdcard = sdcardio.SDCard(spi, cs)
vfs = storage.VfsFat(sdcard)
try:
    storage.mount(vfs, "/sd")
    sys.path.append("/sd")
    sys.path.append("/sd/lib")
    print("SD card mounted.")
except ValueError:
    print("No SD card!")

******************************************

# basic_wifi_test
# 10/16/2025

# SPDX-FileCopyrightText: 2022 Liz Clark for Adafruit Industries
#
# SPDX-License-Identifier: MIT

from os import getenv
import ipaddress
import wifi
import socketpool

networks = []
for network in wifi.radio.start_scanning_networks():
    networks.append(network)
wifi.radio.stop_scanning_networks()
networks = sorted(networks, key=lambda net: net.rssi, reverse=True)
for network in networks:
    print("ssid:",network.ssid, "rssi:",network.rssi)

# Get WiFi details, ensure these are setup in settings.toml
ssid = getenv("CIRCUITPY_WIFI_SSID")
password = getenv("CIRCUITPY_WIFI_PASSWORD")

if None in [ssid, password]:
    raise RuntimeError(
        "WiFi settings are kept in settings.toml, "
        "please add them there. The settings file must contain "
        "'CIRCUITPY_WIFI_SSID', 'CIRCUITPY_WIFI_PASSWORD', "
        "at a minimum."
    )

print()
print("Connecting to WiFi")

#  connect to your SSID
try:
    wifi.radio.connect(ssid, password)
except TypeError:
    print("Could not find WiFi info. Check your settings.toml file!")
    raise

print("Connected to WiFi")

pool = socketpool.SocketPool(wifi.radio)

#  prints MAC address to REPL
print("My MAC addr:", [hex(i) for i in wifi.radio.mac_address])

#  prints IP address to REPL
print(f"My IP address is {wifi.radio.ipv4_address}")

#  pings Google
ipv4 = ipaddress.ip_address("8.8.4.4")
print("Ping google.com: %f ms" % (wifi.radio.ping(ipv4)*1000))

Behavior

SD card mounted.
ssid: network1 rssi: -38
ssid: network1 rssi: -39
ssid: network1 rssi: -39
ssid: network1 rssi: -40
ssid: network1 rssi: -42
ssid:  rssi: -75
ssid:  rssi: -75
ssid:  rssi: -76
ssid: network2 rssi: -85
ssid:  rssi: -86
ssid: network3 rssi: -87
ssid: network4 rssi: -88
ssid:  rssi: -90

Connecting to WiFi
Connected to WiFi
My MAC addr: ['0xZZ', '0xZZ', '0xZZ', '0xZZ', '0xZZ', '0xZZ']
My IP address is 192.168.1.144
Ping google.com: 32.999985 ms

Code done running.

[09:02:46.067] Disconnected
[09:02:47.072] Warning: Could not open /dev/tty.usbmodem144101 (No such file or directory)
[09:02:47.072] Waiting for tty device..

*I've edited the network names and MAC address.
pico w disconnects and CIRCUITPY unmounts after "Code done running."

Description

Mounting the sd card and then scanning for wifi networks causes the disconnections...not necessarily immediately nor every time, but eventually. If I don't mount the sd card at all, or mount the sd card after scanning for networks, it seems to work reliably. If I don't scan for networks, everything works as it should no matter when the sd card is mounted.

Additional information

pico w with picow bell proto underplate and Adafruit datalogger; also pico w with Cytron Maker Pi Pro.

tested with different wifi networks, host computers, USB hubs, cabling, etc.

[dhalbert]

I did some version testing on this, with a somewhat reduced version of the given test program. Sometimes just doing a reset, as opposed to a power cycle, will not produce the USB disconnect. So I always unplugged and plugged in the board to test.

9.2.9 does not have the problem.
10.0.0-alpha.5 caused a safe mode on boot up three or four times in a row.
10.0.0-alpha.6 does not have the problem.
10.0.0-alpha.7 usually disconnects, and so do other versions past that one.

A settings.toml with good credentials should exist, which means that the wifi was already connected when the SD card was mounted. When the credentials were missing, and I the wifi.radio.connect() really did connect, the problem didn't happen. The explicit connect is removed in the test below.

import board, busio, digitalio, sdcardio, storage, sys, time

sck = board.GP18
si = board.GP19
so = board.GP16
cs = board.GP17

print("Sleep 5 seconds")
time.sleep(5)
print("continuing after 5 second sleep")

# This is just to allow me to edit code.py without it running. Spending a lot of time here may cause the problem not to happen, but it's not clear.
wait = digitalio.DigitalInOut(board.GP2)
wait.pull = digitalio.Pull.UP
print("Wait for GP2 to be ungrounded...")
while not wait.value:
    pass

#  SPI setup for SD card
spi = busio.SPI(sck, si, so)
sdcard = sdcardio.SDCard(spi, cs)
vfs = storage.VfsFat(sdcard)
try:
    storage.mount(vfs, "/sd")
    print("SD card mounted.")
except ValueError:
    print("No SD card!")

import ipaddress
import wifi
import socketpool

print("scanning...")
networks = []

for network in wifi.radio.start_scanning_networks():
    networks.append(network)
wifi.radio.stop_scanning_networks()
networks = sorted(networks, key=lambda net: net.rssi, reverse=True)
for network in networks:
    print("ssid:",network.ssid, "rssi:",network.rssi)

pool = socketpool.SocketPool(wifi.radio)

#  pings Google
ipv4 = ipaddress.ip_address("8.8.4.4")
print("Ping google.com: %f ms" % (wifi.radio.ping(ipv4)*1000))

print("code.py finished")