To avoid the accumulation of conversion error, the count in timer driver should use the same time unit as the hardware. BTW, your timer driver has to implement the up_alarm_xxx functions.
Unfortunately, 32.768KHz is a very common clock frequency and it cannot be handled by the current logic. Without a massive overhaul of the timing definitions, the only solution that I know is keep a RAM copy of the time that has been corrected for the differences in precision.
