def test_dispersionCalcForError(self):
"""With non-zero error contribution, the dispersion at different times is additional to that of the parent clock, both before and after the correlation time"""
a = self.newSysClock(tickRate=1000)
b = CorrelatedClock(a, 1000, correlation=Correlation(0, 0, 0.5, 0.1))
self.assertEquals(
a.dispersionAtTime(10) + 0.5 + 0.1 * 10 / 1000,
b.dispersionAtTime(10))
self.assertEquals(
a.dispersionAtTime(20) + 0.5 + 0.1 * 20 / 1000,
b.dispersionAtTime(20))
self.assertEquals(
a.dispersionAtTime(-10) + 0.5 + 0.1 * 10 / 1000,
b.dispersionAtTime(-10))
def algorithm(self):
candidateClock = CorrelatedClock(self.clock.getParent(),
tickRate=self.clock.tickRate,
correlation=self.clock.correlation)
while True:
update = False
cumulativeOffset = None
candidate = (yield self.timeoutSecs)
t = self.clock.ticks
currentDispersion = self.clock.dispersionAtTime(t)
if candidate is not None:
candidateClock.correlation = candidate.calcCorrelationFor(
self.clock, self.localMaxFreqErrorPpm)
candidateDispersion = candidateClock.dispersionAtTime(t)
update = candidateDispersion < currentDispersion
if update:
pt = self.clock.toParentTicks(t)
adjustment = candidateClock.fromParentTicks(pt) - t
if cumulativeOffset is None:
cumulativeOffset = 0
else:
cumulativeOffset += adjustment
self.clock.correlation = candidateClock.correlation
self.onClockAdjusted(
self.clock.ticks, adjustment,
1000000000 * currentDispersion,
1000000000 * candidateDispersion,
self.clock.correlation.errorGrowthRate)
else:
pass
# update worst dispersion seen so far
self.worstDispersion = max(self.worstDispersion,
currentDispersion,
candidateDispersion)
co = cumulativeOffset or 0 # convert None to 0
self.log.info(
"Old / New dispersion (millis) is %.5f / %.5f ... offset=%20d new best candidate? %s\n"
% (1000 * currentDispersion, 1000 * candidateDispersion,
co, str(update)))
else:
self.log.info("Timeout. Dispersion (millis) is %.5f\n" %
(1000 * currentDispersion, ))
# retry more quickly if we didn't get an improved candidate
if update:
time.sleep(self.repeatSecs)
else:
time.sleep(self.timeoutSecs)
class FilterLowestDispersionCandidate(object):
"""\
Simple filter that will reject a candidate unless its dispersion is lower than that currently
being used by the clock.
Note that at initialisation, the clock's dispersion is forced to +infinity.
"""
def __init__(self, clock):
"""\
:param clock: A :class:`~dvbcss.clock.CorrelatedClock` object representing that will be adjusted to match the Wall Clock.
"""
self.clock = clock
self.clock.correlation = clock.correlation.butWith(
initialError=float("+inf"))
self.tmpClock = CorrelatedClock(self.clock.getParent(),
self.clock.tickRate)
def checkCandidate(self, candidate):
self.tmpClock.correlation = candidate.calcCorrelationFor(self.clock)
t = self.clock.ticks
if self.clock.dispersionAtTime(t) > self.tmpClock.dispersionAtTime(t):
return True
else:
return False
def test_dispersionCalcForZeroError(self):
"""With zero error contribution, the dispersion at different times is the same as for the parent clock"""
a = self.newSysClock(tickRate=1000)
b = CorrelatedClock(a, 1000, correlation=Correlation(0, 0))
self.assertEquals(a.dispersionAtTime(10), b.dispersionAtTime(10))
self.assertEquals(a.dispersionAtTime(20), b.dispersionAtTime(20))