[time-nuts] A (slightly) different apu2 question
elfchief-timenuts at lupine.org
Wed Nov 16 18:24:06 EST 2016
So there's been a lot of discussion going around on how to do GPS foo on
pcengines.ch's apu2 hardware, but there's one question I haven't seen
discussed ... which I'm now going to discuss. Or at least ask about.
I can't find a public datasheet for the actual processor in these (a AMD
GX-412TC SOC), but looking at datasheets for similar AMD chips, this SOC
seems to use a single 48MHz external crystal from which all the other
system clocks are derived (save for the 32.768kHz RTC).
On the apu2, this crystal is easily accessible (at least as easy as
anything SMD is). Can anyone think of a reason that it wouldn't be
feasible to replace this crystal with an external reference, à la the
widely known clockblock + Soekris net4501 hack (but with 64x the RAM)? I
figure the higher frequency might make it a bit trickier to get the
signal to the board intact, but is there any other good reason this
The CPU itself is four cores (no hyperthreading), so I'm figuring
dedicate one core to PPS handling (should give really low-jitter
interrupt handling), maybe one to ntpd, and combined with that precision
reference, a pretty nice NTP/PTP server should pop out the other side.
The ethernet on the apu2 even does hardware timestamping.
Can anyone think of a reason this wouldn't work, before I break out the
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