[U-Boot] [RFC][Timer API] Revised Specification - Implementation details

[Wolfgang Denk]

Dear "J. William Campbell",

In message <4DDEAFE0.8060905 at comcast.net> you wrote:
>
> I certainly agree using 64 bits for all calculations is vast overkill. 
> In fact, I think using 64 bit calculations on systems that have only a 
> 32 bit or less timer register is probably overkill. :-) However, to 
> date,AFAIK,  no processor has exceeded the u32 in ticks per second. As I 

Not yet. But it makes no sense to start a new design with settings
already in critical range, especially since there is zero problem
with breaking it down by a factor of 1000 or 1e6.

> pointed out in a previous e-mail, if they ever do this, we can just drop 
> one or 2 bits off the 64 bit counter and in millisecond resolution, 
> nobody will ever know.  Also as previously pointed out, usec2ticks is 

No. I will not accept a design that is so close on the edge of
breaking.

What is your exact problem with the existing interfaces ticks2usec()
and usec2ticks() ?

> not present yet in lots of implementations. Also, if the fundamental 
> clock frequency is 32 kHz  (or anything less than 1 MHz), usec2ticks is 
> 0! This probably rules out using it to get ticks per millisec or ticks 
> per sec.

The statement "usec2ticks is 0" makes absolutely no sense as long as
you don't say which argument you pass in.  You get a return value of
0 even for a tick rate in the GHz range if you pass 0 as argument.

Hoewver, usec2ticks(1000) or maybe usec2ticks(100000) will probably
return pretty useful values.

[Note that by passing properly scaled arguments you can also avoid a
number of rounding errors.]


Best regards,

Wolfgang Denk

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