Hard fault: memory access or instruction error on Cytron Maker Nano RP2040 running 10.2.1

[kevinjwalters]

CircuitPython version and board name

Adafruit CircuitPython 10.2.1 on 2026-05-13; Cytron Maker Nano RP2040 with rp2040

Code/REPL

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Behavior

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CircuitPython core code crashed hard. Crikey!
Hard fault: memory access or instruction error.
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Description

I've got some large code which is doing lots of i2c comms, some UART, low frequency PWM to make LEDs flash on GPIO, very occasional neopixel use and using a fair bit of memory including some use of large array.array.

I have the RP2040 running at 200Mhz rather than 125MHz. I looked at https://learn.adafruit.com/circuitpython-safe-mode/overview and it doesn't include over-clocking as a potential cause. About a minute after that hard crash the microcontroller.cpu.temperature was 37 degrees celsius FWIW. The temperature is now printed from the program and it's peaking at 43 (ambient is 30, it's hot over here). Can over-clocking cause that type of hard fault?

I'd had the program running okay for 2 hours yesterday and today it died after about 10 minutes of use today.

Additional information

No response

[tannewt]

Generally I think overclocking could lead to a crash if data doesn't get from one place to another in time. Either a small reproducer or a backtrace with a debugger is needed to determine the cause.

[kevinjwalters]

I am not sure what causes it so can't produce a small piece of code to reproduce it at the moment. Speculating I thought it could be related to UART rx buffering as that can be unpredictable but in my specific case it's not.

I'm going even faster now at 250MHz now to see if it provokes it but it's been fine for many hours. I'll keep a look out for any further faults as the code progresses. I'll capture the output so I get a better idea of what it's doing when/if it goes bang.