Originally I was going to use an RFDuino to control the clock generator. I backed the RFDuinos a few years ago in the crowd funding campaign but never used them as I generally needed more IO or something else wasn't right. Turns out the same thing again. The RFDuino uses pins 5 and 6 for I2C. I wired it up but found the I2C bus unstable. It would constantly reset. I had a sketch that would set a frequency and every 10 seconds query the Si5351 for it's top register.

Hello
SYS_INIT: 1  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 1
SYS_INIT: 0  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 3
SYS_INIT: 0  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 3
SYS_INIT: 1  LOL_A: 1  LOL_B: 0  LOS: 1  REVID: 1

Looking at the RFDuino spec, it doesn't have a voltage regulator but accepts 1.8-3.6v. I was powering off USB but using the 3V and the GPIO pins are 0.7 * Vdd so I think the clock generator was resetting constantly.

Going back out to the shed I found an OLD Arduino Nano (so old it has a mini-USB port on it) but it worked fine and was able to run the Adafruit Si5351 library and see a signal at my test frequency at 145.225MHz, and the update of the register was working well too:

Hello
SYS_INIT: 1  LOL_A: 1  LOL_B: 0  LOS: 1  REVID: 1
SYS_INIT: 0  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 3
SYS_INIT: 0  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 3
SYS_INIT: 0  LOL_A: 0  LOL_B: 0  LOS: 0  REVID: 3