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Unknown pulsing on STM32L073RZ

Adam Mitchell
Associate II

Hi there,

I'm working with an STM32L073RZ CPU and Mbed OS 5.12.0 and experiencing an issue that I'm not quite sure how to describe. The processor gets into a state whereby it oscillates a pin (PA_5 which is setup as an InterruptIn that pulls down) and also has periodic power spikes that are inversely correlated to the state of PA_5 - this can be seen in the image below. As soon as this issue occurs the CPU seems to no longer be responsive, suggesting that it has crashed.

0690X000008j8PjQAI.png

I am working on a custom board, but I've verified that this issue occurs on a Nucleo-L073RZ development board too.

At first I thought that I may be running out of memory as the issue seemed only to occur when manipulating strings (as, unfortunately, I need to serialise to JSON). However, monitoring memory usage with the API provided by Mbed shows that I am using only a fraction of available memory.

The issue has also occurred when attempting to read an integer via scanf from a hardware UART that is connected to a SIM800 modem.

Both causes seem to be string manipulation related but I'm really not sure what else to check aside from memory usage.

Any insights are greatly appreciated.

4 REPLIES 4

Does your Hard Fault handler output anything helpful? Make sure it and things like Error_Handler() output entry warnings

https://www.st.com/resource/en/datasheet/stm32l073rz.pdf

PA5 is specifically called out with respect to current injection susceptibility.

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There’s nothing from the hard fault handler, or any error handler, unfortunately - no UART output at all. Can’t even connect over SWD due to some bugs with ST-Link Utility.

I wouldn’t be totally surprised if there was current injection on the custom board, but on the dev board the pin is simply broken out as a GPIO.

For this sort of thing you'd probably want to ping your local FAE, probably a known issue

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Figured this out in the end - I was running out of memory. I'm not quite sure where as Mbed's memory management API reported a fair amount of available memory. Alas, adjusting heap/stack sizes and some creative scoping fixed the issue.