Part Number: AM3358
I'm looking at ways to use the RTC on the AM335x.It's likely I'll just need RTC operation for clock/calendar features and not RTC only low-power mode. However, I still want to preserve the RTC clock between resets and possibly via battery when the MPU is shutdown.
Here are my questions.
1. The documents are pretty clear about VDDS_RTC and that we need to keep this supplied with 1.8V at all times and we also need to not assert RTC_PWRONRSTn if we intend to keep the clock running and keeping time. What's not clear is CAP_VDD_RTC. I understand that if I want to use the internal LDO, which I assume outputs 1.1V, then I need to tie RTC_KALDO_ENz low and then tie a capacitor between CAP_VDD_RTC and ground. In this scenario, what's supplying the input to the LDO? Is it VDD_CORE, or is it sourced from VDDS_RTC? The real question I'm getting at, if I want to shut down the MPU (VDD_MPU and VDD_CORE set to 0V) but keep the RTC running, is the VDDS_RTC rail the only one I need to keep supplied? What about CAP_VDD_RTC?
2. The RTC on the AM335x has a feature for calibration called crystal compensation. How is this handled in Linux? Is there a utility we run to perform the calibration and store the values into the RTC?
Thanks
