Now, that may be a bit tricky as your u8x8 object is probably global at the moment, and so any call to Trill::begin() will only take place after that. Teensyduino is the name of the PJRC software that adds features and libraries that support the Teensy boards on the Arduino IDE. So, I'd recommend that you ensure that all of the Trill objects' begin() method (which in turn calls Wire.begin()) are called before you construct the u8x8 object, so that the latter will override any pin setting done by Wire.begin(). My guess is that while Wire may do some pin initialisation, it won't care if someone changes that afterwards, as long as you keep using the same bus (0). Brian 'nox771' has written an improved I2C library for Teensy 3.0. Download: Wire is included with Arduino Richard Gemmell has written an improved I2C library for Teensy 4.0.

As SDA0/SCL0 are the same signals used normally by Wire on the Teensy 3.6 - and without any specific knowledge of the library or of the board - I can try to make a guess. Wire Library The Wire library allows you to communicate with I 2 C devices, often also called '2 wire' or 'TWI' (Two Wire Interface). The Trill library currently uses the Wire library for I2c communication, so whether that one does any initialisation pertaining the functionality of the pins under the hood, I am not sure.

Teensy wire library