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SARPi Project - Slacking on a Raspberry Pi
Install a DS3234 Real Time Clock on a Raspberry Pi running Slackware ARM
This SARPi mini-project will enable you to connect and install a DS3234 real time clock (RTC) with Slackware ARM using the SPI interface on a Raspberry Pi. There are many reasons why connecting a real time clock to the Raspberry Pi is prudent and beneficial, as the device doesn't come with a RTC installed as standard. So we thought it would be interesting, as well as educational and fun, to give our Slackware ARM system on a Raspberry Pi its own real time clock. In this mini-project we'll be installing a Ks0166 keyestudio DS3234 high precision real time clock module.
This mini-project covers how to install a DS3234 RTC using the SPI interface. The most common RTC modules, such as the DS1307, DS3231, PCF8563, RV3028, (etc.) use the I2C interface. The only real difference between these interfaces are the methods used to communicate. SPI is generally quicker than I2C but requires more GPIO pin connections. For a real time clock, access speed shouldn't be an issue whatsoever. Therefore, the most suitable RTC that should be used always depends on requirements and/or personal preference.
For quick reference within this DS3234 RTC guide:
• Required elements for this mini-project
• Connecting the DS3234 RTC to a Raspberry Pi
• Configuring Slackware ARM to use the DS3234 RTC on a Raspberry Pi
• Manually setting the DS3234 RTC to the correct time & date
What you will need for this mini-project
• A Raspberry Pi with a 40-pin GPIO header running Slackware Linux.
• A DS3234-based RTC module, such as the Ks0166 keyestudio DS3234 or SparkFun DeadOn RTC Breakout - DS3234.
• Suitable cables to connect the DS3234 RTC to your RPi (as required).
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Connecting the DS3234 RTC to a Raspberry Pi
A total of 6 [six] connections are required. Refer to the illustration below and ensure the connections are correct. Full details of the Raspberry Pi general-purpose input/output pins can be found on the Raspberry Pi GPIO documentation page, should you need them.
IMPORTANT! : Connect all the DS3234 RTC pins WITHOUT the Raspberry Pi powered on! Ensure everything is powered OFF to avoid any mishaps and/or damage during the wiring connection process!
Once the DS3234 has been connected to the Raspberry Pi and all wired pin connections have been checked and verified, insert the CR1225 battery into the DS3234 battery holder and make sure the polarity is correct.
Now it's safe to power on the Raspberry Pi and boot into the Slackware ARM operating system.
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Configuring Slackware ARM to use the DS3234 RTC on a Raspberry Pi
In order for the kernel to know that there's a DS3234 RTC connected to the system, and what to do with it, at boot time, a 'dtoverlay' entry needs to be specified in the '/boot/config.txt' file. This is easily achieved using a text editor. Here we'll use 'nano', like this:
If the following line within the '/boot/config.txt' file has a hash '#' in front of it - e.g. it looks like this: #dtparam=spi=on - remove the hash '#' to enable the SPI interface:
Somewhere within the '/boot/config.txt' file, enter the following line to load the DS3234 RTC Device Tree overlay at boot time. It can be put anywhere as long as it is on a line on its own.
Save and exit the '/boot./config.txt' file, and then reboot the system...
After rebooting, check the RTC has been detected on the system and works as expected.
root@slackware:~# dmesg | grep ds3234
root@slackware:~# hwclock -r
NB: If you receive an error when querying the RTC with 'hwclock -r' then remember to set the time correctly on the RTC initially! See: Setting the RTC to the correct time & date section below.
The following screenshot shows the output of these commands:
This confirms that the DS3234 RTC is working as expected.
Please note that the output format of RTCs can differ, even when using the same [DS3234] controller. As long as you see the date and time that's expected it's all good.
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Setting the RTC to the correct time & date
If the DS3234 RTC has not already been set to the correct time (e.g. if this is the first time it's been configured on the system) then you might need to do this initially. This can be achieved in two ways: manually using the 'date' command, or by utilising a NTP server on the Internet with the 'sntp -sS' or 'ntpdate' command. NTP servers are preferred for accuracy reasons alone if an Internet connection is available.
Either of the following methods will enable you to set the date/time on the DS3234 RTC. Or most other RTCs in fact.
• Set the time and date on the DS3234 RTC manually by using the following command (pay attention to the date format):
The month (MM), day (DD), hour (HH), and minute (mm) values are always specified in 2 digits and have a leading zero '0' when applicable. The time is always specified as the 24 hour clock. The year (YYYY) value is always specified by 4 digits.
Example: if the time is 9:17pm on September 11, 2016 then the command would be as follows:
In our example above the 'date 091121172016' command sets the time and date on our Slackware Linux system and the 'hwclock -w' command which follows then writes that date and time to the hardware clock (the DS3234 RTC).
• Set the time and date on the RTC using a NTP server with either of the following commands:
root@myrasbox:/tmp# ntpdate pool.ntp.org && hwclock -w
The 'sntp' and 'ntpdate' commands grab the current date and time from a NTP server (from pool.ntp.org in this example) and writes it to our Slackware Linux system. The 'hwclock -w' command which follows then writes that date and time to the hardware clock (the DS3234 RTC). The NTP server you use does not have to be the same one as in our example. There are literally hundreds of NTP servers located around the world that can be called on for this task.
NB: The 'sntp -sS' and/or 'ntpdate' command(s) can be used at any time (as 'root' user) to set the time & date on the system.
The following screenshot shows the output of these commands:
The "Cannot open KoD db file /var/db/ntp-kod: No such file or directory" error can be ignored when using the 'sntp' command. The command output shows that it's successfully set the date/time accurately. When the DS3234 RTC has been detected and is working on the system, the 'hwclock -w' command option will always write the current system time to it.
Useful tip: see the 'man hwclock' documentation on your Slackware Linux system for more details on how to use the time clocks utility.
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Thanks!
Thank you for reading and taking part in this SARPi mini-project. We hope you enjoyed it and found it interesting and educational.
Thanks to Phil Elwell at Raspberry Pi Ltd. for adding the DS3234 SPI RTC in the Raspberry Pi kernel Device Tree overlays after initially suggesting that it should be added as a standard overlay. Kudos and thanks to Nigel Bajema for his "Raspberry PI and your SPI Real Time Clock (RTC)" Science Gizmo (AU) blog that laid down the groundwork for the DS3234 RTC on the Raspberry Pi 2 in 2015.
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Thanks also to Patrick Volkerding, and the entire Slackware Team, for producing a truly wonderful OS. Without you, and the work you do, the SARPi Project would not exist.
If you have any questions or need help, visit the Slackware Linux Forum on Linux Questions. Or get in touch on the #SARPi IRC channel on irc.libera.chat.
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