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by the__alchemist 805 days ago
It's surprising that it was left out. Ie, the workaround makes sense, but this is a peripheral that is sometimes built into MCUs themselves. For example, most (all?) STM32s include an RTC... with the caveat that if you are using them for canonical use cases, you will need external hardware in the form of a dedicated 32kHz oscillator, and possibly a battery.

For a lot of micro-controller timing uses, they aren't required; for example, hardware timers based on the primary clock source, or the Cortex-M systick, but for maintaining accurate dates and times over long periods, the RTC is the right tool. It can also output the dates and times in a convenient format as well, as long as you find named register fields convenient!
3 comments
AdamH12113 805 days ago
An RTC really needs a battery, and even a smaller battery like a 1220 takes up a fair bit of board space -- space that could be used for another connector or more functionality. And even if you have an RTC, you still have to handle the edge case where the battery dies or is removed and the clock resets. Critical low-level internet services probably shouldn't require clients to already have the correct time.

I use an external RTC with a Raspberry Pi for some sensor systems I work with. Its purpose is to give a reasonable chance of having the correct time for recording data in remote locations where no internet connection is available at startup. For a Pi that only provides network services (and thus always needs a working internet connection), I probably wouldn't think to bother.

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01HNNWZ0MV43FF 805 days ago
I had to support an IoT device once that lacked an RTC.

That was actually the easier hardware platform, because it either had good NTP sync or it didn't reach our C&C servers.

The difficult one was the platform that had an RTC. Those would slooowly drift out of sync if NTP was broken. Slowly and silently.

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numpad0 805 days ago
RTC is just an electronically readable Casio watch, it's not even responsible for keeping real time while OS is running. All it does is always incrementing regardless of motherboard power state so to provide time as OS loads.
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