[ntp:questions] [ATOM (PPS) Refclock] Capture assert AND clear
juergen.perlinger at t-online.de
Tue Apr 21 21:46:41 UTC 2015
On 04/21/2015 09:41 AM, f.hiesinger wrote:
> Hi Folks,
> I'm sourcing a pps-signal via GPIO on a raspberry Pi(debian whezzy).
> The pps0 is configured to capture "Assert" AND "Clear" (mode =
> 0x11f3). The internal echo-mechanism is used, so reception of BOTH
> edges is required. Up to here everything works fine.
> When ntp (incl. ATOM Driver 22) is starting, it instantly
> reconfigures* the pps0-behavior to maintain either Assert OR Clear
> Edges. fudge -> flag2 1 inverts the behavior. Any suggestions, how to
> prevent ntpd from reconfiguring the pps-source?
> * in detail, this pps-modebits are removed at the start of ntpd:
> PPS_CAPTURECLEAR 0x02 (depends on flag2)
> PPS_OFFSETASSERT 0x10
> PPS_OFFSETCLEAR 0x20
> PPS_ECHOASSERT 0x40
> PPS_ECHOCLEAR 0x80
That behaviour is pretty much hardwired into ntpd. I think this is done
to reduce the work needed in kernel space, but that's a wild guess.
Anyway, I checked the sources, and I don't see a way to avoid this
behaviour without changes in the code, some of them in places that are
considered mission critical.
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