Customer uses CLK_32KHz from PLL for RTC, but find the RTC time is not accuracy, some board count ahead, some boards count behind, from TRM, the divider would provide a accurate 32.768KHz clock, so the RTC time should also be accurate. Is it the nature of counting RTC with the clock from PLL? or something else?
The 48-MHz clock is further divided by a fixed /2
divider and a fixed /732.4219 divider to create an accurate 32.768-KHz clock for Timer and debounce use.
Paul,
As customer did not manually configure RTC clock source, thought it is default internal RTC32KCLK from PLL, actually read back register RTC_OSC_REG, value is 0x48, RTC clock sourced from external 32KHz, Seems it is configured in UBoot although did not find the code location.
Now the problem is the RTC calendar ahead or behind real time several minutes every 24-hours. sometimes just after calibrate the time, it drift 3-4 seconds after 2 minutes.
RTC connection as below:
Did further experiments:
Remove external 32-KHz crystal, with the same software, after each power cycle, the RTC still can count, but calendar start from a fixed/default date 13-1-1 0:0:0.
reinstall the 32KHz crystal, calendar keep on counting, did not change to default date after power cycle, just drift several minute every 24 hours.
I found a similar post as below, but it use 32K_aux_clk, and did not post the detail method on how to solve it.
