The Zynq® UltraScale+™ MPSoC real time clock (RTC) provides the real time even when the device is powered off. When the device is off, the RTC is switched to the battery power supply. A battery-backed RAM (BBRAM) is provided for when device is operating in the battery mode. However, the RTC controller and user interface are only operational when the low-power domain supply is ON. The RTC has an alarm function that generates an alarm at a specific time and date with a 136-year range. The RTC also has periodic software calibration and logic to correct the static fractional inaccuracy of an oscillator.
Real-Time Clock (RTC) provides the following features:
- Maintains the real time, even when the device is off (powered-off).
- Has the capability to generate an alarm at a specific time and date.
- Includes the means for periodic software calibration of the RTC.
- Includes logic to correct the static fractional inaccuracy of the oscillator.
- Keeps track of time within a window of more than 136 years (232 seconds) from a reference point.
- Implemented as three counters.
- 16-bit tick counter creates one second based on the crystal clock.
- 4-bit fraction counter keeps track of the static crystal errors in one second that is less than one oscillator tick.
- 32-bit seconds counter holds the real time and allows on-demand reload whenever current time of the RTC is set.
- Allows wake-up at a specific second within the 136 years (32-bit alarm)
Missing features, Known Issues, limitations
Overview of Linux RTC Frameworkhttp://lxr.free-electrons.com/source/Documentation/rtc.txt
This weblink is path to rtc.txt file in linux documentation which clearly expalins about the legacy and new framework for RTC on SoC.
Kernel Configuration:Kconfig options:Menuconfig snapshots -
This driver is currently in sync with the mainline kernel except for the following:
rtc: zynqmp: Add calibration set and get support
- rtc: zynqmp: Clear alarm interrupt status before interrupt enable
- rtc: rtc-zynqmp: Add calibration set and get support
- a4704c54 :Add calibration set and get support
- rtc: rtc-zynqmp: Clear alarm interrupt status before intr enable
- 771fb636 rtc: rtc-zynqmp: Clear alarm interrupt status before intr enable