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Table of Contents

Introduction

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.

HW/IP FEATURES:

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

  • None

Info

For Calibration register corruption, refer 000036886 - RTC clock time is incorrect due to calibration register corruption

Overview of Linux RTC Framework

http://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:

Code Block

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config RTC_DRV_ZYNQMP
        tristate "Xilinx Zynq Ultrascale+ MPSoC RTC"
        depends on OF
        help
          If you say yes here you get support for the RTC controller found on
          Xilinx Zynq Ultrascale+ MPSoC.
 
 

Menuconfig snapshots -

Code Block

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[*] EDAC (Error Detection And Correction) reporting  --->
[*] Real Time Clock  --->
[*] DMA Engine support  --->
[*] Auxiliary Display support  --->


Code Block

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themeMidnight
--- 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 ***

Testing Procedure

Code Block

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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.
 

Mainline status

This driver is currently in sync with the mainline kernel

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ChangeLog

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  • 2025.1

  • None

2020.2

...

    • Summary:

      • rtc: zynqmp:

...

  • 2020.1

    • summary:
      • rtc: rtc-zynqmp: Add calibration set and get support
    • Commits
      • a4704c54 :Add calibration set and get support
  • 2019.2

    • Summary
      • rtc: rtc-zynqmp: Clear alarm interrupt status before intr enable
    • Commits
      • 771fb636 rtc: rtc-zynqmp: Clear alarm interrupt status before intr enable
  • 2019.1

    • None
  • 2018.3

    • None
  • 2018.2

    • None
  • 2018.1

    • None
  • 2017.4

    • None
  • 2017.3

    • None
  • 2017.2

    • None

...

2017.1

  • None

2016.3

...

      • Fix optional clock name property

    • Commit:

  • 2024.2

    • None

  • 2024.1

    •  Summary

      • rtc: zynqmp: Convert to platform remove callback returning void

    • Commit

  • 2023.2

    • None

  • 2023.1

    • Summary

      • rtc: zynqmp: initialize fract_tick

    • Commit

Related Links

http://lxr.free-electrons.com/source/Documentation/rtc.txt