[En-Nut-Discussion] NutGetTickClock rounding (again)

[Henrik Maier]

There has be some discussion about a better implementation and bug-fix of
NutTimerMillisToTicks (refer to posts in 2006, subject "Request for Comment:
NutTimerMillisToTicks()").

This has been applied in recent Nut/OS releases (>4.2.1 onwards).

However the current implementation does only round for the special case when
the result would be 0 (see if clause below). However for other cases with
small ms values it does not round at all and we end up with large errors
(50%) for small ms values in cases where NutGetTickClock() is just below
1000, for example 997. For clock frequencies where NutGetTickClock() is
greater than 1000 it does not matter but for cases where it is less than
1000 it results in unnecessary inaccuracies. 

I came across this issue when recently upgrading from Nut/OS 4.2.1 to 4.4.1
and some of my time-out calculations did not work anymore as they were too
short.
	

Current implementation:
-----------------------

u_long NutTimerMillisToTicks(u_long ms)
{
    u_long x;
    
    x = ms * NutGetTickClock() / 1000UL;
    if (x == 0) {
        x = 1;
    }
    
    return (x);
}

I suggest to replace above implementation with proper rounding applied which
will work for a broader range of use cases incl. different clock frequencies
and ms values:

Suggested implementation:
-------------------------
u_long NutTimerMillisToTicks(u_long ms)
{
    return (ms * NutGetTickClock() + 500) / 1000UL;
}



Regards

Henrik