Enabling RTC on Inforce Platforms
Introduction: The purpose of an RTC or a real-time clock is to provide precise time and date which can be used for various application use-cases. Similar to a watch, it runs on a battery and keeps time for you even when there is a power outage on your system! Using it, you can keep track of long timelines, even if your system is disconnected from the power plug.
Snapdragon processors seamlessly integrate Power Management ICs that typically include RTC support natively. Inforce platforms based on Snapdragon processors thus have RTC feature onboard or provide a means through which off-the-shelf coin cells with cable assemblies can be connected. This removes the need for an additional IC and related circuitry to achieve this implementation.
A typical block diagram of the PMIC with all major building blocks is shown below
Clock distribution and real time clock are part of the General Housekeeping block. The real time clock functions are implemented by a real time counter and an alarm, both configurable in one-second increments. The primary input to the RTC circuits is the selected sleep-clock source (calibrated low-frequency oscillator, or a crystal oscillator). Even when the system is powered off, the oscillator and RTC can continue to run off other sources like a coin cell or super capacitor. As power is restored, the RTC pauses and skips a few seconds.
Inforce platforms will reacquire system time from the network to resume the usual RTC accuracy. If the voltage at VCOIN drops too low for some reason, RTC contents are again corrupted. An oscillator stop can also cause real-time clock errors. All these errors are handled by Inforce platforms using interrupts and the real-time clock accuracy is guaranteed.
Inforce systems typically retain the correct time without drift for a minimum of 5 weeks of power down, with the coin cell battery being fully charged when the system was powered down.
Inforce 6309 micro SBC and Inforce 6640 SBC platforms have the RTC feature onboard and the accompanying Android and Linux BSPs support this feature out-of-the-box. The Snapdragon 600 based Inforce 6410P SBC provides a 2-pin header to which a coin cell can be plugged in to realize the RTC feature (with a bit of software of course). Inforce computing would be glad to help customers to implement the real-time clock feature on custom carrier boards designed for any of their micro SoM products.