[U-Boot] [RFC] Review of U-Boot timer API

Graeme Russ
2011-05-25T06:06:31Z

Hi Wolfgang,

On Wed, May 25, 2011 at 3:28 PM, Wolfgang Denk <wd@denx.de> wrote:
> Dear "J. William Campbell",
>
> In message <4DDC6F46.4090809@comcast.net> you wrote:
>>
>> ? ? ? ? Well, it is not quite that simple. The "accuracy" of the 1 ms
>> interrupt rate is controlled in all cases I know about by the resolution
>> of the programmable divider used to produce it. It appears that the x86
>
> I mentioned a couple of times before that accuracy has never been a
> design criterion. ?Please also keep in mind that there are areas in
> the code where we block interrupts, and we make zero efforts to detect
> or compensate for this in the timer code. ?This simply is not
> important. ?We are not talking about ppm here, we are talking about
> somting that is just good enough for what it is being used, and that
> allows easily for +/- 10% tolerances.

With the prescaler design we are discussing, as long as we have access to
a free-running tick counter, it does not matter one iota if the interrupt
is delayed by one tick, a hundred ticks or a thousand ticks privided it
eventually happens within the roll-over interval of the tick counter

And if get_timer() is called in the meantime, the roll-over interval gets
reset

Regards,

Graeme