RevPi3 on Ubuntu

[StefanoBossi]

Dear forum members,
I have successfully installed the latest Ubuntu 22.04 on the Rev Pi Core, now I would like to configure the Real Time Clock.
I have loaded the rtc-pcf2127 driver

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root@ubuntu:~# lsmod | grep rtc
rtc_pcf2127            24576  0

but I can't see the device on the i2c bus:

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root@ubuntu:~# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

And no rtc under /dev is present.

What I have to do to load properli the module?

Thanks,
Stefano Bossi

[StefanoBossi]

I think I need to compile and install an overlay, could you point me in the direction of the right one?

Thanks,
S.

[dirk]

Hi this sounds like an exciting project please have a look at the following links
https://github.com/RevolutionPi
https://kunbus-gmbh.atlassian.net/servi ... 2002399028

[nicolaiB]

You can have a look at our overlay files. They are located in our kernel repository. The overlay for the Core 3(+) / Core S can be found here: https://github.com/RevolutionPi/linux/b ... verlay.dts

Nicolai

[StefanoBossi]

Hi Dirk,
thanks for the link but I need a little more help.
Here what I tried.
* the overlay I found in https://github.com/RevolutionPi are here: https://github.com/RevolutionPi/linux/t ... s/overlays the one that seems promising is the

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revpi-core-overlay.dts

.
Unfortunately I can't compile the overlay because there are some includes I can't find the source.
So I have extracted the portion I am interested:

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/dts-v1/;
/plugin/;

/ {
    fragment@3 {
            target = <&i2c1>;
            __overlay__ {
                    pinctrl-names = "default";
                    pinctrl-0 = <&i2c1_pins>;
                    #address-cells = <1>;
                    #size-cells = <0>;
                    status = "okay";

                    rtc@51 {
                            compatible = "nxp,pcf2129";
                            reg = <0x51>;
                            status = "okay";
                    };

                    crypto@60 {
                            compatible = "atmel,atecc508a";
                            reg = <0x60>;
                            status = "okay";
                    };
            };
    };
};

I have installed the needed tools for compiling the stuff:

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sudo apt-get install flex bison swig device-tree-compiler

and I have compiled the extracted Device Tree

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dtc -o dtb -o 2129.dtbo -@ ./2129.dts

loaded the DT in the Kernel with this trick:

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mkdir -p /sys/kernel/config/device-tree/overlays/2129
cat 2129.dtbo > /sys/kernel/config/device-tree/overlays/2129/dtbo

Unfortunately no success
The rtc is not there.

I have tried the old fashioned way of loading a module:

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modprobe rtc_pcf2127
echo pcf2129 0x51 /sys/class/i2c-adapter/i2c-1/new_device

Even in this try, no success

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root@ubuntu:~# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

I think I am pretty close but I miss something.

What do you think I am doing wrong?
Any suggestion ?

Thanks,
S.

[StefanoBossi]

I have tried with

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dtoverlay=i2c-rtc,pcf2127

but no success.
The

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/dev/rtc

is not there and

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i2cdetect

is still empty
Reading syslog I found an error:

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Mar  8 08:48:16 ubuntu kernel: [    2.807099] rtc-pcf2127-i2c: probe of 1-0051 failed with error -121

What does it mean? Wrong address?
I think I am on the right direction I just miss the last step.

[StefanoBossi]

Finally I found a solution!!!!
No building custom modules is needed, only stock kernel configuration.
Here the trick is that the I2c used bus IS NOT THE STANDARD ONE (i.e. usually con Raspberry the I2c bus is on GPIO 2 and GPIO 3, which on Kunbus are used for other pourpose).
The GPIO where the RTC is attached are the GPIO 44 and GPIO 45, you could check on the provided schematic and you could even see that there are the two pull up resistors needed by the bus to properly work.

That was the difficult thing to spot, as soon as I have understood that I have decided to configure a second I2c bus and let the RTC driver use that.

1. Configure the Tree Overlay

I have added these two lines to

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/boot/firmware/config.txt

:

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      dtoverlay=i2c-gpio,i2c_gpio_sda=44,i2c_gpio_scl=45,bus=2
      dtoverlay=i2c-rtc,pcf2129

The first one configure the second I2c bus and assign the correct 2 GPIO, the second one ask to the kernel to use the driver for the pcf2129 for RTC.

• Create a Service for Systemd

In the service you have to create a new device when the system start up:

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[Unit]
Description=RTC configuration for pcf2129

[Service]
ExecStart=/usr/local/bin/configrtc.sh

[Install]
WantedBy=multi-user.target

This is the script used in the service:

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#!/bin/bash
echo pca2129 0x51 > /sys/class/i2c-dev/i2c-2/device/new_device
sleep 0.5
hwclock -s || hwclock -w

In this way I have the RTC device working at startup every time with my Ubuntu Server 22.04.

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root@kunbus02:~# i2cdetect -y 2
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- 51 -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Hope that this little tutorial could be of some help to some other users.

Regards,
S.