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refclock: add new refclock for RTCs

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This refclock uses an RTC as reference source. If the RTC doesn't
support reporting an update event this source is quite coarse as it
usually needs a slow bus access to be read and has a precision of only
one second. If reporting an update event is available, the time is read
just after such an event which improves precision.

Depending on hardware capabilities you might want to combine it with a
PPS reference clock sourced from the same chip.

Note that you can enable UIE emulation in the Linux kernel to make a RTC
without interrupt support look like one with irqs in return for some
system and bus overhead.

Co-authored-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
This commit is contained in:
Uwe Kleine-König
2021-06-30 16:47:21 +02:00
committed by Miroslav Lichvar
parent 65be9d9a02
commit 4f22883f4e
4 changed files with 203 additions and 3 deletions
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3
refclock.c
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@@ -48,6 +48,7 @@ extern RefclockDriver RCL_SHM_driver;
extern RefclockDriver RCL_SOCK_driver;
extern RefclockDriver RCL_PPS_driver;
extern RefclockDriver RCL_PHC_driver;
extern RefclockDriver RCL_RTC_driver;
struct FilterSample {
double offset;
@@ -160,6 +161,8 @@ RCL_AddRefclock(RefclockParameters *params)
inst->driver = &RCL_PPS_driver;
} else if (strcmp(params->driver_name, "PHC") == 0) {
inst->driver = &RCL_PHC_driver;
} else if (strcmp(params->driver_name, "RTC") == 0) {
inst->driver = &RCL_RTC_driver;
} else {
LOG_FATAL("unknown refclock driver %s", params->driver_name);
}