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 -
tristate "Xilinx Zynq Ultrascale+ MPSoC RTC"
depends on OF
If you say yes here you get support for the RTC controller found on
Xilinx Zynq Ultrascale+ MPSoC.
[*] EDAC (Error Detection And Correction) reporting --->
[*] Real Time Clock --->
[*] DMA Engine support --->
[*] Auxiliary Display support --->
--- Real Time Clock
[*] Set system time from RTC on startup and resume
[*] Set the RTC time based on NTP synchronization (NEW)
(rtc0) RTC used to set the system time
[ ] RTC debug support
*** RTC interfaces ***
[*] /sys/class/rtc/rtcN (sysfs)
[*] /proc/driver/rtc (procfs for rtcN)
[*] /dev/rtcN (character devices)
[ ] RTC UIE emulation on dev interface
< > Test driver/device
*** Platform RTC drivers ***
< > ST M48T86/Dallas DS12887
< > ST M48T35
< > ST M48T59/M48T08/M48T02
< > Oki MSM6242 (NEW)
< > TI BQ4802
< > Ricoh RP5C01 (NEW)
< > EM Microelectronic V3020
<*> Xilinx Zynq Ultrascale+ MPSoC RTC (NEW)
*** on-CPU RTC drivers ***
1.Get current date and time using "date" command
2.Set date and time using following commanddate -s "2015-09-08 13:36:00"
3. Verify the same using date command again.
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