The official document says:most 32.768-kHz crystals have a frequency tolerance of ±20 parts per million (ppm) at +25 °C.
a crystal with 20- ppm error in nominal frequency can drift the clock accuracy by 52 seconds in a month.
But now the drift is about 10 seconds only after 2 or 3 days.What could be the reason of it? Is there any solution?
I am noticing the same issue as well. The drift in my case is approximately 2 seconds every 14 hours.
I applied the RTC patch and I am following the RTC example app. I am not sure what is the cause of this.
I would like to know if there is any explanation about this.
Forgot to mention that I am using BCM20737S.
Possible reasons I can think of: Power supply fluctuations, different temperature than 25 °C, humidity?
(And there could always be a software/firmware issue somewhere )
Temperature is certainly a suspect here. Everything else seems to be setup correctly.
Does anyone know how to correctly use "void bleapputils_changeLPOSource(UINT8 pmu_clkSrc, BOOLEAN selSlaveLPOSrc, UINT16 driftRate);"?
What is the rule for determining the driftRate value in this function?
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Drift rate is usually in ppm (parts per million)
This excel sheet might be useful: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwiQhbax-4nYAhXLx4MKHaHuBqUQFggr…
Not sure about the accuracy of it however....
Here's an online one that is similar: Real-Time Clock Calculator - Maxim
I would suspect the driftrate value is the PPM drift of the clock as compared with an "accurate" clock to determine the constant drift rate you need to compensate for.