[rtems commit] pps: Round to closest integer in pps_event()
Sebastian Huber
sebh at rtems.org
Thu Mar 9 06:54:14 UTC 2023
Module: rtems
Branch: master
Commit: d5c386ff99933c2e71e2119b395cd0470a772a0b
Changeset: http://git.rtems.org/rtems/commit/?id=d5c386ff99933c2e71e2119b395cd0470a772a0b
Author: Sebastian Huber <sebastian.huber at embedded-brains.de>
Date: Mon Feb 27 14:49:10 2023 -0700
pps: Round to closest integer in pps_event()
The comment above bintime2timespec() says:
When converting between timestamps on parallel timescales of differing
resolutions it is historical and scientific practice to round down.
However, the delta_nsec value is a time difference and not a timestamp. Also
the rounding errors accumulate in the frequency accumulator, see hardpps().
So, rounding to the closest integer is probably slightly better.
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/604
---
cpukit/score/src/kern_tc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
index 0aa0fdd393..95ae01b5b4 100644
--- a/cpukit/score/src/kern_tc.c
+++ b/cpukit/score/src/kern_tc.c
@@ -2266,6 +2266,7 @@ pps_event(struct pps_state *pps, int event)
#ifdef PPS_SYNC
if (fhard) {
uint64_t delta_nsec;
+ uint64_t freq;
/*
* Feed the NTP PLL/FLL.
@@ -2277,7 +2278,8 @@ pps_event(struct pps_state *pps, int event)
tcount &= captc->tc_counter_mask;
delta_nsec = 1000000000;
delta_nsec *= tcount;
- delta_nsec /= captc->tc_frequency;
+ freq = captc->tc_frequency;
+ delta_nsec = (delta_nsec + freq / 2) / freq;
hardpps(tsp, (long)delta_nsec);
}
#endif
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