Those are (mostly) esp-idf libraries; the sources are in esp-idf. See e.g. here for how they get built.

ESP-Spirit I'm not sure what you mean by "Are you powering the ESP32 through the 3.3V generated by that Cp2104 chip, perhaps?". I am using the USB cable. In all likelihood, that USB cable either uses the CP2104 chip in it as the source for 3.3V, or has some other small LDO that delivers it. Either ...

Are you powering the ESP32 through the 3.3V generated by that Cp2104 chip, perhaps?

From what I call, the esp_timer subsystem does callbacks from its own task; it may be configurable in Menuconfig on what core it runs. Esp_timer is a shared resource as in: if something else has scheduled a callback at the same time as your program, your callback could be delayed until the earlier c...

Do you have enough decoupling on your voltage lines? Especially with a slow-reacting power supply, putting a few uF near the ESP32 itself may help. (Also, only just saw you're using ESP-IDF 3.0 - that one went out of support a while ago. Not saying it'll solve your issue, but you may want to think o...

You're probably better off poking sales @ espressif . com with this question; they have experience getting people through testing procedures like that.

A busy interrupt could impact how everything else that is CPU bound runs, but I'm having a hard time explaining e.g. the baud rate change, as this is something set in hardware. Can I ask what hardware you are using, and would you be OK with sharing code that shows this effect?

The only thing I can think of is that display.display() is still doing things even after the call itself returns; as the mutex is unlocked after, perhaps the 2nd thread overwrites some information it uses. You'd need to take a good, hard look at the lib code to see if that's true, though.

Still sounds like a power issue, to be honest... I am applying 3.6V on VIN with 1A limit on a power supply so it can't come from power supply I guess. VIN? Of what devboard? Many devboards have a regulator that requires a larger voltage difference between Vin and the output 3.3V. For instance, the A...

Are you sure you're using an USB cable capable of data transfers, and not one that is power-only?