RTClib¶

TIMESTAMP · DS3231 · PCF8563 · ADVERT

Every packet MeshCore sends carries a timestamp, and every advert has one. RTClib supplies the clock those timestamps come from — whether or not the node has a real RTC chip on board.

[!NOTE] Source. This page was verified against the firmware itself: MeshCore v1.16.0, commit 03b6ef4, 28 July 2026 — files platformio.ini, src/helpers/AutoDiscoverRTCClock.cpp, src/helpers/RTC_RX8130CE.h and the examples/ directory.

What it does¶

RTClib by Adafruit talks to real-time clock chips over I²C. It knows the DS3231, DS1307 and PCF8563 among others, each with its own class, and supplies the DateTime type for calculating with moments in time — to and from unix time, with calendar conversion. The repository is at github.com/adafruit/RTClib.

How MeshCore pulls it in¶

platformio.ini r.24

  adafruit/RTClib @ ^2.1.3

In [arduino_base], so in all 507 build targets. RTClib is additionally declared separately in seven variant files.

How MeshCore uses it¶

The RTClib classes come together in AutoDiscoverRTCClock, which scans the I²C bus for a clock chip at start-up:

src/helpers/AutoDiscoverRTCClock.cpp r.6-16

static RTC_DS3231 rtc_3231;
static bool ds3231_success = false;

static Melopero_RV3028 rtc_rv3028;
static bool rv3028_success = false;

static RTC_PCF8563 rtc_8563;
static bool rtc_8563_success = false;

static RTC_RX8130CE rtc_8130;
static bool rtc_8130_success = false;

Two of those four classes come from RTClib (RTC_DS3231, RTC_PCF8563), one from another library (see rv3028.md) and one from MeshCore itself. The DateTime type from RTClib is also used by the GPS time synchronisation in src/helpers/sensors/MicroNMEALocationProvider.h r.5.

The example sketches include the library directly:

examples/simple_repeater/MyMesh.h r.3-6

#include <Arduino.h>
#include <Mesh.h>
#include <RTClib.h>
#include <target.h>

In total, eleven of the 590 source files name RTClib: six under src/ and five in examples/ — the three MyMesh.h files of simple_repeater, simple_room_server and companion_radio, plus SensorMesh.h of simple_sensor and main.cpp of simple_secure_chat.

What it means for a node¶

A node without an RTC chip works fine, but only keeps time while it is powered. After a restart the counter starts again, unless the time is set from outside — through the CLI, through a companion app or through GPS. A node with one of the four supported clock chips remembers the time across a restart, and that shows in the timestamps on received messages and in how adverts play out.

Sources¶

Translated from Dutch by Anthropic Claude