[time-nuts] A (slightly) different apu2 question

Mike Cook michael.cook at sfr.fr
Thu Nov 17 03:42:18 EST 2016

Sorry if this is a dup. I had accidentally left the « SPAM » prefix on my first reply.

> Le 17 nov. 2016 à 00:24, Jay Grizzard <elfchief-timenuts at lupine.org> a écrit :
> 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).

The principle should be applicable…. BUT you had better look closely at the schematics. There are some very low voltages in there.

> 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 wouldn't work?
> 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 rework gear?
> -j
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