Zero/dev/RTC module ds3231

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 Radxa Zero >  Development >  RTC module ds3231 

enable i2c overlay

use rsetup to enable I2C_EE-M3 if you don't know how to use rsetup, you can refer [here]

pin

zero                 ds3231
pin 3                sda
pin 5                scl
gnd                  gnd
vcc                   vcc

then reboot your Radxa Zero

checkout device

• make sure that i2c_ee-m3 was enabled

root@radxa-zero:/home/radxa# ls /dev/i2c-*
/dev/i2c-3  /dev/i2c-5

• check the i2c address of the RTC module

root@radxa-zero:/home/radxa# i2cdetect -r -y 3
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- -- 

add a new rtc device

• add a new rtc device

root@radxa-zero:/home/radxa# echo ds3231 0x68 | sudo tee  /sys/class/i2c-adapter/i2c-3/new_device

• checkout the new rtc device

root@radxa-zero:/home/radxa# ls /dev/rtc*
/dev/rtc  /dev/rtc0 /dev/rtc1

read time from rtc module

root@radxa-zero:/home/radxa# hwclock -r -f /dev/rtc1
2000-01-01 00:01:40.083622+08:00

set time

root@radxa-zero:/home/radxa# apt-get install ntp -y
root@radxa-zero:/home/radxa# sudo service ntp start

or
date -s "2023-05-09 15:16:35"

write time to rtc module

• write time to rtc module after you make sure the time of linux is right

root@radxa-zero:/home/radxa# hwclock -w -f /dev/rtc1

• then read the hardware RTC at the time to see if it is correct

root@radxa-zero:/home/radxa# hwclock -r -f /dev/rtc1
2023-05-09 15:18:45.390726+08:00

• to set the Linux system time to the hardware RTC time

 hwclock -s -f /dev/rtc1

• use timedatectl to view all the time information

root@radxa-zero:/home/radxa# timedatectl
               Local time: Tue 2023-05-09 15:21:49 CST
           Universal time: Tue 2023-05-09 07:21:49 UTC
                 RTC time: Thu 1970-01-01 00:04:27
                Time zone: Asia/Shanghai (CST, +0800)
System clock synchronized: no
              NTP service: n/a
          RTC in local TZ: yes

Warning: The system is configured to read the RTC time in the local time zone.
         This mode cannot be fully supported. It will create various problems
         with time zone changes and daylight saving time adjustments. The RTC
         time is never updated, it relies on external facilities to maintain it.
         If at all possible, use RTC in UTC by calling
         'timedatectl set-local-rtc 0'.

set automatic startup

root@radxa-zero:/home/radxa# touch /etc/rc.local
root@radxa-zero:/home/radxa# chmod 777 /etc/rc.local
root@radxa-zero:/home/radxa# cat /etc/rc.local
#! /bin/bash

echo ds3231 0x68 | sudo tee  /sys/class/i2c-adapter/i2c-3/new_device
sudo hwclock -s -f /dev/rtc1