This API was introduced for 2 reasons:
1. Some hardware can emit PPS signals but not starting from arbitrary
absolute times, but rather phase-aligned to the beginning of a
second. We _could_ patch ts2phc to always specify a start time of
0.000000000 to PTP_PEROUT_REQUEST, but in practice, we would never
know whether that would actually work with all in-tree PHC drivers.
So there was a need for a new flag that only specifies the phase of
the periodic signal, and not the absolute start time.
2. Some hardware can, rather unfortunately, not distinguish between a
rising and a falling extts edge. And, since whatever rises also has
to fall before rising again, the strategy in ts2phc is to set a
'large' pulse width (half the period) and ignore the extts event
corresponding to the mid-way between one second and another. This is
all fine, but currently, ts2phc.pulsewidth is a read-only property in
the config file. The kernel is not instructed in any way to use this
value, it is simply that must be configured based on prior knowledge
of the PHC's implementation. This API changes that.
The introduction of a phase adjustment for the master PHC means we have
to adjust our approximation of the precise perout timestamp. We put that
code into a common function and convert all call sites to call that. We
also need to do the same thing for the edge ignoring logic.
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Now that we are registering a clock even for the PPS master when it
supports that (i.e. when it is a PHC), introduce a new API to retrieve
its clock in order to add timestamps to it.
The PHC master can be synchronized to the extts events of a PHC slave,
when in automatic mode.
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
This propagates the use of "struct ts2phc_private" all the way into the
master API, in preparation of a new use case that will be supported
soon: some PPS masters (to be precise, the "PHC" kind) instantiate a
struct clock which could be disciplined by ts2phc.
When a PHC A emits a pulse and another PHC B timestamps it, the offset
between their precise timestamps can be used to synchronize either one
of them. So far in ts2phc, only the slave PHC (the one using extts) has
been synchronized to the master (the one using perout).
This is partly because there is no proper kernel API to report the
precise timestamp of a perout pulse. We only have the periodic API, and
that doesn't report precise timestamps either; we just use vague
approximations of what the PPS master PHC's time was, based on reading
that PHC immediately after a slave extts event was received by the
application. While this is far from ideal, it does work, and does allow
PHC A to be synchronized to B.
This is particularly useful with the yet-to-be-introduced "automatic"
mode of ts2phc (similar to '-a' of phc2sys), and the PPS distribution
tree is fixed in hardware (as opposed to port states, which in
"automatic" mode are dynamic, as the name suggests).
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
This patch introduces a new ts2phc source using a PHC device. There
are multiple use cases for such a master. By connecting pins of two
or more separate PHC devices together, one may act as the source, and
the others may be synchronized to it in hardware. In this way, "just
a bunch of devices" together forms a Transparent Clock. If the master
clock is synchronized to a global time source (like a PPS from a GPS),
then the system becomes a mutli-port Grand Master or a Boundary Clock
with GM capability.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Vladimir Oltean
Richard Cochran