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    hwclock works in normal devices that have RTC - it writes and reads from it. There are iOT devices without an RTC. Commented Feb 26, 2019 at 16:35
  • I assume you are referring to the Raspberry Pi case, where a fairly advanced embedded device lacks a hardware clock capable of RTC. Raspberry Pi is a example of an outlier, because it tries to offer an enormous range of capabilities at as low of a price as possible, hence they chose to save money by forgoing a built-in battery powering one tiny IC capable of RTC. Commented Feb 26, 2019 at 16:44
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    The rpi suffers from it, but it is not alone, unfortunately. Commented Feb 26, 2019 at 16:46
  • Unfortunately the we are using the BusyBox 1.24.1 hwclock which as far as I can tell can only write to and from the system time. Writing directly to hwclock would be ideal but doesn't seem to be available to me: BusyBox v1.24.1 (2018-11-14 12:40:41 PST) multi-call binary. Usage: hwclock [-r|--show] [-s|--hctosys] [-w|--systohc] [-t|--systz] [-l|--localtime] [-u|--utc] [-f|--rtc FILE] Commented Feb 26, 2019 at 17:07
  • Here is the hwclock implementation. I believe the -f option just allows us to point hwclock to a specific rtc. Commented Feb 26, 2019 at 17:24