Real Time Clock

The Real Time Clock (RTC) is a circuit that runs off a small battery or a super capacitor connected to VBAT. It needs its own crystal and keeps running even when the main system and its clocks are powered off.

.NET

using var rtc = new RtcController();

var time = new DateTime(2024, 1, 1, 10, 59, 50, DateTimeKind.Utc);
rtc.DateTime = time;

// Read some time later
var rtc_time = rtc.DateTime;

Python

import datetime
from GHIElectronics.Endpoint.Devices.Rtc import RtcController

rtc = RtcController()

time_ = datetime.datetime(2024, 1, 1, 10, 59, 50, tzinfo=datetime.timezone.utc)
rtc.DateTime = time_

# Read some time later
rtc_time = rtc.DateTime

C/C++

#include <chrono>
#include <endpoint/Rtc.h>

using namespace GHIElectronics::Endpoint::Devices::Rtc;

RtcController rtc;

auto time = std::chrono::system_clock::now();
rtc.DateTime(time);

// Read some time later
auto rtcTime = rtc.DateTime();

VBAT

VBAT mode can be set in "charger mode" where it can charge an attached supercap.

info

Make sure the RTC battery charge mode is correctly set. Charging a lithium coin cell may cause damage to the cell and could cause it to leak.

.NET

using var rtc = new RtcController();

rtc.SetChargeMode(BatteryChargeMode.Fast);

Python

from GHIElectronics.Endpoint.Devices.Rtc import RtcController, BatteryChargeMode

rtc = RtcController()

rtc.SetChargeMode(BatteryChargeMode.Fast)

C/C++

#include <endpoint/Rtc.h>

using namespace GHIElectronics::Endpoint::Devices::Rtc;

RtcController rtc;

rtc.SetChargeMode(BatteryChargeMode::Fast);

System clock

The system clock is seeded from the RTC at boot: once the RTC is set and VBAT keeps it running, DateTime.Now (or the equivalent Python / C++ clock) returns the right time on every subsequent boot without any extra setup. Set the RTC once:

.NET

using var rtc = new RtcController();
if (!rtc.IsValid) {
    rtc.DateTime = new DateTime(2024, 1, 30, 15, 0, 0, DateTimeKind.Utc);
}

Python

import datetime
from GHIElectronics.Endpoint.Devices.Rtc import RtcController

rtc = RtcController()
if not rtc.IsValid:
    rtc.DateTime = datetime.datetime(2024, 1, 30, 15, 0, 0, tzinfo=datetime.timezone.utc)

C/C++

#include <chrono>
#include <endpoint/Rtc.h>

using namespace GHIElectronics::Endpoint::Devices::Rtc;

RtcController rtc;
if (!rtc.IsValid()) {
    auto t = std::chrono::sys_days{std::chrono::January / 30 / 2024}
           + std::chrono::hours(15);
    rtc.DateTime(t);
}