svn commit: r244287 - projects/calloutng/sys/x86/isa

[Adrian Chadd]

Have you guys even remotely verified that all the weird i8254 clones
support this operation?

Considering our track record with breaking some of the legacy hardware
(and preventing stable operation on things like Alix boards), I'd
really like to see this particular option hide behind a runtime or
build config twiddle.

Thanks,


Adrian


On 16 December 2012 03:16, Alexander Motin <mav at freebsd.org> wrote:
> Author: mav
> Date: Sun Dec 16 11:16:13 2012
> New Revision: 244287
> URL: http://svnweb.freebsd.org/changeset/base/244287
>
> Log:
>   Mostly out of fun, teach i8254 eventtimer driver to program only LSB for
>   very short time intervals (<214us).  This allows to get less then 22us
>   usleep(1) time from this anscient timer.  It is even better then HPET time
>   now, just with much higher CPU usage.
>
> Modified:
>   projects/calloutng/sys/x86/isa/clock.c
>
> Modified: projects/calloutng/sys/x86/isa/clock.c
> ==============================================================================
> --- projects/calloutng/sys/x86/isa/clock.c      Sun Dec 16 10:12:40 2012        (r244286)
> +++ projects/calloutng/sys/x86/isa/clock.c      Sun Dec 16 11:16:13 2012        (r244287)
> @@ -125,6 +125,7 @@ struct attimer_softc {
>  static struct attimer_softc *attimer_sc = NULL;
>
>  static int timer0_period = -2;
> +static int timer0_last = 0xffff;
>
>  /* Values for timerX_state: */
>  #define        RELEASED        0
> @@ -433,11 +434,17 @@ set_i8254_freq(int mode, uint32_t period
>                 outb(TIMER_CNTR0, new_count >> 8);
>                 break;
>         case MODE_ONESHOT:
> +               if (new_count < 256 && timer0_last < 256) {
> +                       outb(TIMER_MODE, TIMER_SEL0 | TIMER_INTTC | TIMER_LSB);
> +                       outb(TIMER_CNTR0, new_count & 0xff);
> +                       break;
> +               }
>                 outb(TIMER_MODE, TIMER_SEL0 | TIMER_INTTC | TIMER_16BIT);
>                 outb(TIMER_CNTR0, new_count & 0xff);
>                 outb(TIMER_CNTR0, new_count >> 8);
>                 break;
>         }
> +       timer0_last = new_count;
>  out:
>         mtx_unlock_spin(&clock_lock);
>  }