Internal RC oscillator is specified up to 8MHz, but in reality it can be calibrated to run at up to 12MHz. V-USB has code that does this. HaD, please, work on your terminology.

This is an Arduino Library for the STP3593LF (ROX5242T1N) Digitally-Controlled Double-Oven Crystal Oscillator from rakon. It allows you to fully configure the oscillator over I 2 C. Examples are ...

This is an Arduino Library for the SiT5358 Digitally-Controlled Temperature-Compensated Crystal Oscillator from SiTime. It allows you to fully configure the oscillator over I 2 C. Examples are ...

Rather handily, this unit is compatible with 3.3V Shield, fully conforming to the Arduino R3 Layout. To add on to this board you'll have Atmel's Embedded Debugger, EDBG, ...

To signal devices that accept both the 20- and 25-Hz standards, the oscillator may be designed for 22.5 Hz (R1, R2, and R3 at 27.4 kΩ and R4 at 953 kΩ), permitting adequate frequency stability ...