diff options
Diffstat (limited to 'docs/devel/clocks.rst')
| -rw-r--r-- | docs/devel/clocks.rst | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst index f0391e7..956bd14 100644 --- a/docs/devel/clocks.rst +++ b/docs/devel/clocks.rst @@ -360,6 +360,18 @@ rather than simply passing it to a QEMUTimer function like ``timer_mod_ns()`` then you should be careful to avoid overflow in those calculations, of course.) +Obtaining tick counts +--------------------- + +For calculations where you need to know the number of ticks in +a given duration, use ``clock_ns_to_ticks()``. This function handles +possible non-whole-number-of-nanoseconds periods and avoids +potential rounding errors. It will return '0' if the clock is stopped +(i.e. it has period zero). If the inputs imply a tick count that +overflows a 64-bit value (a very long duration for a clock with a +very short period) the output value is truncated, so effectively +the 64-bit output wraps around. + Changing a clock period ----------------------- |