[time-nuts] Beaglebone NTP server

[Gabs Ricalde]

As an alternative to the Net4501, the AM335x in the Beaglebone has
timers that accept an external clock up to 25 MHz (TCLKIN) and can
timestamp events on an input pin (TIMER4-TIMER7). Both sets of pins are
available on the headers after an appropriate pinmux configuration.

I'm finishing the clocksource driver for Linux, I'm testing it using the
10 MHz and PPS outputs of a LEA-6T. ntpd loopstats show +/- 0.1 us
offsets, frequency is a flat 0.000 PPM as expected.