External RTC clock mod requires apollo 3 register change. How?

External RTC clock mod requires apollo 3 register change. How?#228441

By Atorr - Mon Sep 13, 2021 12:46 pm

- Mon Sep 13, 2021 12:46 pm #228441

I'm replacing the 32.768KHz crystal in the RTC with a very stable clock, following the recommendations given here:
https://support.ambiq.com/hc/en-us/arti ... pollo-MCUs.
In addition to some hardware mods, it requires changing the register XTALGENCTRL value to 0, but do not know how. I am using the OLA Artemis board.

Re: External RTC clock mod requires apollo 3 register change. How?#228442

By TS-Russell - Mon Sep 13, 2021 4:03 pm

- Mon Sep 13, 2021 4:03 pm #228442

It looks like that address is "ADDRESS: 0x40020124" - I'd think you just call that register and write 0x00 in its place?

You might also post this as a request on the ambiq page linked above

Re: External RTC clock mod requires apollo 3 register change. How?#228445

By Atorr - Mon Sep 13, 2021 7:18 pm

- Mon Sep 13, 2021 7:18 pm #228445

TS- thank you. Yes, that is what needs to be done. Just do not know how to do it in the arduino environment. I looked at HAL use in the open log artemis code, but did not see any that I could use.

Re: External RTC clock mod requires apollo 3 register change. How?#228504

By Atorr - Thu Sep 16, 2021 8:04 pm

- Thu Sep 16, 2021 8:04 pm #228504

Response from Gary, Ambiq Micro tech support: (Thank you, it worked!!)

To write to the register we recommend using the following CMSIS register access method.
For example
uint32_t val = MCUCTRL->XTALGENCTRL; // Read the XTALGENCTRL register
MCUCTRL->XTALGENCTRL_b.XTALBIASTRIM = 0;

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