[SOLVED] J-Trace with STM32WB

juliengros · Apr 26th 2023, 6:41am

Hi,

We are designing a new board and consider ETM trace IOs. I could not find any "tracing recommendation for STM32WB" on wiki.
Do you confirm that J-trace should work with this ST chip famly. Are there any board design recommendations besides those (wiki.segger.com/Trace_board_design_recommendations) to consider? Side note: being limited on IOs, we might have to mux the trace lines with UART lines. Wonder whether this could mean issues/drawbacks?

BR,
Julien

SEGGER - Nino · Apr 26th 2023, 5:08pm

Hello Julien,

Thank you for your inquiry.
According to the STM32WB reference manual only the STM32WB55 series has an ETM + TPIU. So if you are using any of the smaller variants instruction tracing will not be available.
But if you have a STM32WB55 you can trace it if your board implements the necessary trace connector:
wiki.segger.com/UM08001_J-Link…2FSWD_and_Trace_connector

juliengros wrote:

Are there any board design recommendations besides those (wiki.segger.com/Trace_board_design_recommendations) to consider? Side note: being limited on IOs, we might have to mux the trace lines with UART lines. Wonder whether this could mean issues/drawbacks?

This fits to the following generic advice from our Wiki:
"Avoid multi usage of trace pins with other ICs which again will cause unwanted impedance changes and reflection"

So while it is not recommended it does not mean it will not work. Especially as the STM32WB only runs with max. 64 MHz CPU speed which translates to 32 MHz trace clock you should be good.
Worst case you need to design some jumper disconnect for the UART stuff when you are tracing, but I do not think that will be necessary.
In my experience the parasitic effects start to become problematic in the >50MHz trace clock speed area.

Usually we would suggest to simply follow the eval board design from ST. Unfortunately it appears that currently there is no trace capable eval board available from ST for the STM32WB series which is also why we do not have an example project with trace pin init yet as we usually do for popular devices:
segger.com/products/debug-prob…echnology/tested-devices/

Best regards,
Nino

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