Failed to connect to STLink V3 using a USB isolator

SZENG.1 · ‎2020-03-24

Dear,

I expected to connect my PC to a STLink-V3 debugger (either on nucleo G4 board or a standalone one) via a USB isolator but failed.

While, I can connect to the nucleo directly without isolator, I also can connect the nucleo board with a STLink V2 on board

Beside, the PC can recognize the STLink V3 correctly, which means the device can be found in the 'Device Manager', but the ST-Link Utility just cannot talk to it, which says 'communicaiton error'

I'm wondering what's wrong, anyone can help?

Many thanks

S C · ‎2020-03-25

Hello,

I confirm that the STLINK-V3 implements commands only on the High Speed USB interface, and not on the Full Speed one. Which will explain the issue, if the isolator is not supporting the USB HS. It is not currently planned to degrade/duplicate the STLINK-V3 interface in Full Speed.

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TDK · ‎2020-03-24

Did you try to reduce the SWD frequency? Likely just a poor isolator.

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SZENG.1 · ‎2020-03-24

Hi TDK,

When isolator is used, the Utility cannot identify the STLink V3 correctly, so no setting can be performed:

Here is the snapshot without isolator for comparison:

I also feel that it is because of the speed of the isolator, then I'm wondering what's the requirement to the isolator? how fast should it be? what kind of standard should it comply to?

waclawek.jan · ‎2020-03-24

USB isolator is most likely FS (12Mbit/s) whereas STlink V3 is HS capable of 480Mbit/s. It appears that the FS portion of the STLink FW is implemented only formally, not providing any real functionality just minimal descriptors.

JW

PS

@Amel NASRI , could please somebody comment on this?

S C · ‎2020-03-25

Hello,

I confirm that the STLINK-V3 implements commands only on the High Speed USB interface, and not on the Full Speed one. Which will explain the issue, if the isolator is not supporting the USB HS. It is not currently planned to degrade/duplicate the STLINK-V3 interface in Full Speed.

SZENG.1 · ‎2020-03-25

Got it! Many thanks!

Markus Rudolf · ‎2020-05-04

So ST sells USB products violating the USB spec then?

S C · ‎2020-05-04

The FS USB descriptors are provided, the USB spec is respected. But there are no proprietary commands implemented behind. The ST-Link debug interface is a proprietary one.

Markus Rudolf · ‎2020-05-04

Well technically maybe yes, practically if it just does not work in 12 MBit Mode and there is no obvious reason why it shouldn't I call it broken :)