Just curious, since I'm trying to build a Leonardo-compatible-ish board... I see the 32u4RC-AU chip out there with a built in oscillator, but the leo and most other boards use an external crystal with the non-RC chip. Is there a reason to avoid the internal oscillator? Is it just not accurate enough?
21.4 Crystal-less operation
To reduce external components count and BOM cost, the USB module can be configured to operate in low-speed mode with internal RC oscillator as input source clock for the PLL. The internal RC oscillator is factory calibrated to satisfy the USB low speed frequency accuracy within the 0°C and -40°C temperature range.
For USB full-speed operation only external crystal oscillator or external source clock can be used.
Thanks; exactly what I was looking for, clear and unambiguous. Sorry I missed it.