RE: Can I add HFCLKSRC in nrf51.h?

RK — Sun, 03 May 2015 09:13:14 GMT

HFCLKSRC isn't a register, it's just an internal designation, there is only one place to connect the HF clock source and that's pins XC1 and XC2. You can use a 16 or 32MHz crystal or, according to the manual, a 16MHz external source, here's the relevant piece

The HFCLK crystal oscillators utilize amplitude regulated architecture to achieve low current consumption and fast start-up. The HFCLK crystal oscillators are also designed to work with one of the following alternative external sources:

A 16 MHz rail-to-rail clock signal applied to the XC1 pin. The XC2 pin shall then be left unconnected.
A 16 MHz low swing clock signal applied to the XC1 pin. The XC2 pin shall then be left unconnected.

So external source is specified by leaving XC2 unconnected.

It says nothing there about a 32MHz external reference. The table 11 in chapter 3.6 of the nrf51822 product spec also says you have a choice of 16/32MHz crystal or 16MHz external, no option for 32MHz external is listed there.

I would expect if 32MHz external was available, it would work by connecting the external source to XC1, leaving XC2 unconnected and specifying 32MHz as you have done. If that doesn't work, it's probably because 32MHz external clock is not an available option.