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Raspberry Pi Pico2 W - Wifi fails to start if CPU is overclocked #16799

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chrisib opened this issue Feb 23, 2025 · 5 comments
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Raspberry Pi Pico2 W - Wifi fails to start if CPU is overclocked #16799

chrisib opened this issue Feb 23, 2025 · 5 comments
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bug port-rp2

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@chrisib
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chrisib commented Feb 23, 2025

Port, board and/or hardware

RPI_PICO_2_W

MicroPython version

MicroPython v1.25.0-preview.307.g4364d9411 on 2025-02-23; Raspberry Pi Pico 2 W with RP2350

Reproduction

Save the following code onto the Pico 2 W and run it with either CPU_FREQ = 300_000_000 or CPU_FREQ = 150_000_000 uncommented.

When using the overclocked frequency, the following error is printed and the access point is not available to connect to: [CYW43] Failed to start CYW43

When using the default frequency the access point can be connected to and no errors are printed

import machine
import network
"""
When overclocked we get

[CYW43] Failed to start CYW43


When using default CPU frequency
the wifi starts fine
"""
CPU_FREQ = 300_000_000  # overclocked
#CPU_FREQ = 150_000_000  # default

machine.freq(CPU_FREQ)

wifi = network.WLAN(network.WLAN.IF_AP)
wifi.config(
    ssid="pico2w_ap",
    channel=10,
    security=network.WLAN.SEC_OPEN,
)
wifi.active(True)

Expected behaviour

WiFi should work if the CPU is overclocked

Observed behaviour

When the CPU is overclocked, the wireless card firmware does not appear to initialize correctly:

[CYW43] Failed to start CYW43

Additional Information

My testing setup has 2 I2C devices connected: an OLED display GP0 & GP1 and a battery-backed realtime clock on GP2 & GP3. The code above does not initialize these devices, so I don't think their presence should have any impact; it looks like simply changing the CPU frequency is enough.

Doing a little trial-and-error changing the frequencies in the script above it looks like 270MHz is the upper limit of what the wifi can handle. Is this a known limitation of the firmware?

Code of Conduct

Yes, I agree
@chrisib chrisib added the bug label Feb 23, 2025
@Gadgetoid
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Have you tested against Pico SDK 2.1.1? It has stability fixes for WiFi which might also work here.

There's a branch with it bumped (and the small required fix to CMakeLists) here: https://github.com/dpgeorge/micropython/tree/lib-pico-sdk-211

It should probably go without saying; but nothing is guaranteed when you overclock. It's not a MicroPython limitation specifically but the hardware- and thus the SDK on which the Pico port relies- isn't officially supported at anything but the stock clock. MicroPython kinda leaves the guardrails off a bit here and lets you discover your own board's limits, but aiui does not attempt to make any guarantees about overclocking.

There is, iirc, also a lower limit at which WiFi breaks down. The CYW43 driver is... spicy.

@chrisib
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chrisib commented Feb 25, 2025

I tried out the fork you linked, but I'm still seeing the same Failed to start CYW43 error if I try to create an access point or connect to my home router while the CPU is overclocked.

@Gadgetoid
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It’s probably just pushing the CYW43 bus clock out of range then.

It might be possible to fix this in MicroPython by proportionally raising the clock divider. IE: the opposite to what is discussed here: raspberrypi/pico-sdk#1392

It’s not a function that is currently exposed, but as part of RM2 support maybe it could be added to the hypothetical CYW43 driver module mentioned here: #16057 (comment)

Though it would perhaps make sense for overclocking using “machine.freq()” to take care of this.

@chrisib
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chrisib commented Feb 26, 2025

Good news: the new 1.25.0-preview.314.g8ce7a58be appears to work if I overclock to 250_000_000; it still fails to start at 300_000_000, but it seems like an improvement.

@jonnor jonnor added the port-rp2 label Mar 3, 2025
@KnorkFox
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KnorkFox commented May 5, 2025

This is probably a timing issue, and no bug in micropython. Please close this bug.

@robert-hh robert-hh converted this issue into discussion #17251 May 5, 2025

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@jonnor @Gadgetoid @chrisib @KnorkFox