RTC
The Real Time Clock (RTC) on the phyCORE-AM57x serves the basic purpose of keeping time of day, as well as providing tamper proofing for digital rights management and waking up the rest of the chip from a power down state. The RTC can keep track of the year, month, date, weekday, hour, minute, and seconds and has timer, alarm, and external event input functionality. This guide will show you how to use RTC on the phyCORE-AM57x development kit to verify functionality when power is lost. To learn more information about the phyCORE-AM57x RTC interface, please see section 4 in the Hardware Manual.
RTC |
Description |
|---|---|
rtc0 |
External RTC populated on the SOM at U19 |
rtc1 |
Internal RTC for the AM57x SoC |
rtc2 |
PMIC rtc populated on the SOM at U3 |
Accessing RTC
With your kit powered on and booted into Linux, the first thing to do is to check the name of the RTC device we will be using.
Target (Linux)cat /sys/class/rtc/rtc0/name
Expected Outputrtc-m41t80 0-0068
Note
If the kit is not showing rtc0, the EEPROM configuration could be incorrect and need to be update. See the Using the PHYTEC EEPROM Flashtool guide for more information.
Use the following command to set the system time (this is an arbitrary time, but note that you have to use a time later than the build date of the kernel).
Target (Linux)date 071916142022
Tip
The argument in the above command broken down is: 07-19 16:14 2022 date time year
Setting the Time
Verifying RTC
Now poweroff the kit and remove the power supply! Powering off the kit should be done with this command:
Target (Linux)poweroff
Wait about a minute or so before powering the kit back on and booting into Linux.
Once booted into Linux, use this command to check the time. You should see that the clock was advanced accurately even when the board was turned off.
Target (Linux)hwclock -r -f /dev/rtc0