So, I got past the undefined symbol by adding this to platformio.ini for this board: build_flags = -DCORE_DEBUG_LEVEL=3 -DARDUINO_USB_MODE -DARDUINO_USB_CDC_ON_BOOT=1 It builds, but Serial.println does not result in any text coming back over the connection (yes, I did Serial.begin() ). Strangely (or...

Thanks for the reply. I copied the sdkconfig from core into my project, but I'm still getting no Serial symbol defined, even though this time, HardwareSerial.h has an extern HardwareSerial Serial; in it. Serial is even undefined in the core itself: /Users/ryan/.platformio/packages/framework-arduinoe...

Have you examined esp_now_init()? Maybe the USB connection isn't a red herring and it's actually the issue itself. Perhaps there's something relevant in that function that could offer a clue as to where to look next...

I am writing a library that I'd like to be as portable as possible, and my development boards are all ESP32-based (the board I'm using currently is the Unexpected Maker Feather S3). I had been primarily using PlatformIO, with platform = espressif32 and framework = arduino until yesterday, when I rea...