[U-Boot] core ticks/timer code

Jean-Christophe PLAGNIOL-VILLARD
2009-03-31T11:39:56Z

On 12:28 Tue 31 Mar , Wolfgang Denk wrote:
> Dear Mike Frysinger,
>
> In message <200903310513.09082.vapier@gentoo.org> you wrote:
> >
> ...
> > > I've in mind to partially import the clocksource linux API or create a new
> > > U-Boot api devired from it's design
> >
> > the clocksource framework in linux sounds like extreme overkill for u-boot.
> > where do you see realistic usage of more than one timer ? u-boot is pretty
> > much a single threaded app that polls.
That's why I've tell to partially import it as have done Sascha in u-boot V2
>
> Correct. We definitely do not need the full capabilities of the Linux
> framework. Any new implementation will be checked against the current
> code, and memory foot print is something we will check carefully.
>
> OTOH, I think Sascha's u-boot-v2 uses code that was derived from the
> Linux code, but in a pretty lean way. It may be interesting to check
> there...
I've take a look on it and it's the idea I've in mind to do also
>
> > > I'll propose a new design with the following Requierement
> > >
> > > Generic delay function implementation
> > > - ndelay()
> > > - udelay()
> > > - mdelay()
> > >
> > > Generic helper
> > > - khz2cycles()
> > > - hz2cycles()
> > > - cs2ns()
> > >
> > > Timer API
> > > - timer_init() - setup the timer
> > > - timer_reset() - reset the timer (use in case of overflow)
> > > - get_ticks() - return the current ticks
> > > - get_cycles() - return the ticks frequency in ns
> >
> > do you have real use cases here ? i'd actually propose the opposite: kill off
> > the notion of "ticks", "cycles", and "hz". i dont think ndelay() is really
> > necessary, and mdelay() is a simple macro on top of udelay(). that leaves us
> > with really only the three functions we have today: timer_init(), get_timer(),
> > and reset_timer(). we clarify that the function operates in terms of
> > milliseconds and blam, it's all so simple now.
Yes I've real case where I do need ndelay to generate high speed clock with a
gpio and udelay is too slow.

we need get_cycles and get_ticks to calculate the udelay, mdelay and ndelay
otherwise how can you known the ticks frequency?
>
> Agreed (except that we probably cannot completely throw away the
> tick; IIRC there are cases in early startup when nothing else is
> available yet).
not necessarely you can activate the timer just after the cpu_init
so normally you do not need any get_ticks.

Best Regards,
J.