On Mon, Mar 20, 2023 at 10:36 PM Gregory Nutt <spudan...@gmail.com> wrote:
> > > NuttX offers a function clock_synchronize() that synchronizes system > clock > > with clock from RTC (internal or external). The synchronization is done > > during board initialization and I suppose this can also be called from an > > application level if required. > I think clock_synchronize() is okay for startup initialization, but > would be inappropriate at run time. That is because it could cause the > current time to apparently jump backward. That could be fatal under > certain circumstances as described for adjtime() in > https://github.com/apache/nuttx/issues/8858 > I remember once reading about how FreeBSD handles this (I think it was FreeBSD; this was a long time ago): If there is a difference between the system clock and the reference clock, the system clock is _not_ assigned the reference clock's time, exactly because of the "clock running backwards" problem. Rather, when the clock is advanced, the advancement is adjusted by a small amount, so that the system clock always runs forwards, never backwards, and over time the system clock gradually comes into synchronization with the reference clock. We probably need something like that to avoid the same problem. Cheers Nathan
