[En-Nut-Discussion] NutGetMillis overflow documentation

[uprinz2 at netscape.net]

Thanks Ole, you are right! 
 
Never thought about that. The problem some delay routines have is that the 
calculation for the time may shift out to much bits if the width of the 
registers is not obeyed. But if you stay wwithin the limits, like 
NutGetMillis() does, the value is also precise if an overflow / trunkation 
is done.  
 
Best regards, Ulrich 
 
On Mon, 08 Feb 2010 18:04:11 +0100, Ole Reinhardt 
<ole.reinhardt at embedded-it.de> wrote: 
> Hi! 
>  
>> Normally you do timespan calculations that look like this: 
>>  
>> if( now-past < span) { wait a bit } 
>>  
>> These type of call will result in a jitter with every overflow. 
>  
> That's not correct. As long as now and past are both uint32_t this 
> calculation will work correctly even if there was an overflow between 
> past and now. That's a nice effect of unsigned calculations :) 
>  
> Example (8 bit) 
>  
> Now = 10   = 0x0A 
> Past = 245 = 0xF5 
>  
> now - past = 0x(ffffff)15 => truncated to 8 Bit = 0x15 = 21 (which is 
> totaly correct) 
>  
> Regards, 
>  
> Ole