Add a level shifter for logic signals

[DSTkrt]

If the target core is supplied with a voltage other than 3.3V, driving a signal line high will forward-bias the target pins esd diode, which may be destructive. Segger solves this in their J-Link by having a level shifter between their microcontroller and the target core. ST doesn't care and blasts 3.3V on the core anyways.

I'd suggest adding a bi-directional level shifter behind the ESD protection IC. Proper care needs to be taken when selecting the IC, since they are limited in silly ways. For example:

• NLSX4014 has stupid restrictions on power supplies (as many others do), namely VCCB < VCCA-0.4V
• PI4ULS3V204 is too slow.

Alternatively, an unidirectional with direction control might do, too, the firmware will need to manage the direction of the translation, then...

[adamgreig]

It's not likely any more hs-probe will be made soon due to parts shortages, but there has been work on a new probe here (rusty-probe) which does include level-shifters for 1.8-3.3v.