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i.MX6UL internal SNVS RTC counts too fast

Question asked by Philipp Bachmann on Jan 17, 2019
Latest reply on Jan 18, 2019 by Philipp Bachmann

Dear all, 


I want to use the SNVS RTC with backup battery on imx6ul. I was able to enable it in kernel and device tree. From user space I can read it (hwclock -r) and set it to system time (hwclock -w). However, it runs way to fast, around +8 seconds faster per minute. This is more than 137ms per second. According to iMX6UL reference manual there is an RTC calibration register, however the maximum possible calibration value is 16/32768=488us per second, so no way I can compensate it this way. I know that internal clocks are quite inaccurate compared to external crystals, but I don't believe the difference is that big.


Does anyone have an idea what the problem could be? 


Thanks and regards