While browsing the stm32f051xx datasheet I came across this section (p23, section 3.15, Real-time clock (RTC) and backup registers)
timestamp feature which can be used to save the calendar content. This function can be triggered by an event on the timestamp pin, or by a tamper event. The MCU can be woken up from Stop and Standby modes on timestamp event detection
As I understand it, this allows you to take a snapshot of the date and time that a pin change occurs either with or without waking up. However, there is no further explanation of this feature, even in the RTC application notes.
I could see obvious uses for this feature if you could save multiple timestamps, or it had sub-second accuracy. However, none of that is available. I assume this feature must be commonly useful to be included, so I'm curious what kind of use-cases this feature was designed in mind with.