Leakage current potentially via STLINK pins on demo board?

bigjosh · ‎2024-07-01

I am trying to make some very low current (<1uA) power measurements on the MCU on the STM32U083C-DK demo board.

I see that jumper `JP7` is provided specifically for this purpose, but I am concerned that connections from the MCU to the STLINK interface might leak current and throw off these measurements- especially when testing with MCU Vcc voltages that differ from the STLINK supply voltage.

Is this a valid concern, or are those connections equivalent to air-gapped when the MCU is normally running?

Thanks!

bigjosh · ‎2024-07-03

These Nucleo boards are actually kind of ironic because they copy the superficial *shape* of an air-gappable DMZ, but they have traces that sneak across the gap...

This *exactly* misses the point! 🙂

BarryWhit · ‎2024-07-03

I don't think anyone really expects the ST-Link section to talk to the mainboard MCU by telepathy.

But It is unclear what the point of the slots are. Are customers just supposed to just snap off the embedded ST-LINK? That's definitely one way to air-gap.

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Andrew Neil · ‎2024-07-04

@BarryWhit wrote:
Are customers just supposed to just snap off the embedded ST-LINK? That's definitely one way to air-gap.

yes, that is exactly the point!

https://community.st.com/t5/stm32-mcus-products/stm32-mcu-choosing-and-programming/m-p/657536/highlight/true#M239953

bigjosh · ‎2024-07-04

>I don't think anyone really expects the ST-Link section to talk to the mainboard MCU by telepathy.

The two sides need to talk to each other, but the path by which they do so should be manifest rather than hidden.

On the TI boards, there are no traces in the DMZ. The only things that straddle the border line are the jumpers, and so pulling those jumpers obviously air-gaps the MCU, and does so non-destructively so you can replace the jumpers and go back to debugging after you've made your measurements.

BarryWhit · ‎2024-07-04

> the path by which they do so should be manifest rather than hidden.

If the ST user manual instructs you to snap off the complementary ST-LINK module and reconnect it with a harness to the board, that's pretty "manifest". it's also easy to "visually verify". etc. You like the way TI does it? you're free to do so.

But, you suggested ST didn't even consider the need to completely and provably disconnect the embedded ST-LINK from the rest of the system, and I showed you that you are wrong about that. So now, you dislike the way they do address this need - and that's also your prerogative. I suggest we leave it at that.

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Andrew Neil · ‎2024-07-04

@BarryWhit wrote:
ST didn't even consider the need to totally and provably disconnect the embedded ST-LINK from the rest of the system

It's possible on the Nucleos with the break-off ST-Link, but not on other boards.

The OP's STM32U083C-DK doesn't have the break-off ST-Link.

The LRWAN1 in another without the break-off ST-Link, and it has some obscure & undocumented leakage paths.