Trying to generate a 512 Hz signal that is synchronous to the LSE.
MCU is an STM32L476ZETx.
Measuring the signal on RTC_OUT_CALIB with a Keysight tabletop multimeter. (And also with an oscilloscope.)
Observation:
Setting "RTC_CALIBOUTPUT_1HZ": measured frequency = 999.99 mHz
Setting "RTC_CALIBOUTPUT_512HZ": measured frequency = 496.5x Hz (jittery)
Why is it that the nominally "512 Hz" signal is way out, whereas the 1 Hz is as perfect as can be expected?
My expectation was that the 512 Hz are derived from the same clock and are therefore equally precise. We were planning to use this 512 Hz signal as a common clock for various external peripherals.
I am not entirely convinced that PCB layout has anything to do with this issue, since the 1 Hz signal appears to be working just fine. Happy to be proven wrong, though...
Similar observations seem to have been made by others in the past - with no solutions on file so far:
