Introduction

This project implements a control script for the RTC of the Raspberry Pi CM4IO and similar boards that use the same design, e.g. Cytron's CM4 Maker Board or Waveshare's CM4-boards.

The script is motivated by the fact that the kernel cannot control the alarm-settings of the RTC. The script runs in userspace. It will only work if the kernel is not in control of the RTC, i.e. there is no overlay configured for the PCF85063A.

Software

The software consists of a program to control the RTC and a system daemon which takes care of

setting the system-time after boot (optional)
clearing alarms after boot
setting the alarm (next boot time) at shutdown (optional)

Installation

Clone the archive and then run the install-command from the tools-directory:

git clone https://github.com/bablokb/cm4io_rtcctl.git
cd cm4io_rtcctl
sudo tools/install

Besides changing some system configuration files, this command will mainly install three components (and there prereqs):

cm4io_rtcctl.py, the control program for the real-time-clock
cm4io_rtcctl.service, the systemd-service

After installation, you should reboot your system to activate the changes.

Initializing the real-time-clock

If your real-time-clock is not yet set, you have to initialize it once. Make sure that you have an internet connection so the ntp-daemon updates the system time. Check the system time and the time of the RTC:

date
sudo cm4io_rtcctl.py show date

If the system time is correct and the time matches, you are done. Otherwise initialize the RTC once with:

sudo cm4io_rtcctl.py init

Note that the standard linux tool hwclock will not work, since we don't expose the standard RTC-device interface of the RTC.

For the cm4io-board, a coincell backup-battery is not strictly required as long as the board is powered. Cytron's "CM4 Maker Board" in contrast turns power off after shutdown. This is far more efficient but it makes the coincell mandatory.

Usage

The command /usr/local/sbin/cm4io_rtcctl.py is the main user-interface to the real time clock. With this command, you can read and write the RTC-time, set the alarm time, turn the alarm on, off or clear an alarm that has fired:

[root@cm4:~] # cm4io_rtcctl.py help

Available commands (date and time are synonyms):
     help                                - dump list of available commands
     init                                - initialize RTC
     show  [date|time|alarm|sys]         - display given type or all
     dump  [control|date|time|alarm]     - display registers (hex/binary format)
     set   date|time|alarm|sys           - set RTC-date, alarm, sys-date
                                           Format: dd.mm.YYYY [HH:MM[:SS]] or
                                                   mm/dd/YYYY [HH:MM[:SS]]
                                           (does not turn alarm on!)
     alarm on                            - turn alarm on
     alarm off                           - turn alarm off
     alarm clear                         - clear alarm-flag