RTC for iMX8MP-SOM-EVB-IND

[ilario]

On A64-OLinuXino there was an exposed contact for adding an external battery powering the Real Time Clock present on the board, as explained here, and it was very useful.

Is there something like this for the iMX8MP-SOM-EVB-IND?

Maybe using a UEXT module like the MOD-RTC2? But then, how should one use it? Should one write a Systemd unit probing the RTC and updating the system time? Is there something like that ready to use?

[LubOlimex]

I have to check about built in RTC of iMX8, but using external module like MOD-RTC2 is not very hard as long the I2C communication is properly working. MOD-RTC2 uses a battery to keep the time and I2C for communication and when board get powered on you update system clock from the I2C, there is a demo for A20 board take a look:

https://github.com/OLIMEX/OLINUXINO/tree/master/SOFTWARE/A20/A20-OLinuXino-Micro%20with%20MOD-RTC2

[LubOlimex]

I can see we that we use PCA9450 which one of the recommended by NXP power management chips. It has own quartz, so as long as the PCA9450 is powered it should keep the RTC alive. Also all connection are proper even the lowest power mode is properly connected (SNVS mode). PCA9450 has seven different operating modes (controlled by the input voltage on the VSYS pin and an external control signal (I2C that I inspected is connected between the main chip, the PMU, and the EEPROM).

The PCA9450 doesn't operate on battery tho. It requires 5V DC and from those it makes LDO1 and LDO2. And then if you seek lower power mode, configure the PMU for SNVS mode via the I2C. Refer to these documents:

https://www.nxp.com/docs/en/application-note/AN14246.pdf
https://www.nxp.com/docs/en/data-sheet/PCA9450.pdf

Notice that you can also check what the official NXP forums say since the board uses iMX8 and NXP PMU PCA9450C which is a recommended combo and NXP staff can also provide some insight.