Gilles Chanteperdrix authored Jun 01, 2014 and Philippe Gerum committed Jun 02, 2014

Because timer period is converted to clock ticks when starting a
periodic timer, round-off errors may accumulate at each timer tick
causing the timer to drift. Fix this by keeping the timer period as a
count of nanoseconds and convert to clock ticks at each period. This
adds some overhead, but is more correct.