On Mon, 23 Oct 2000, David Woodhouse wrote:
> See arch/i386/kernel/time.c:
>
> /* This function must be called with interrupts disabled
> * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
> *
> * However, the pc-audio speaker driver changes the divisor so that
> * it gets interrupted rather more often - it loads 64 into the
> * counter rather than 11932! This has an adverse impact on
> * do_gettimeoffset() -- it stops working! What is also not
> * good is that the interval that our timer function gets called
> * is no longer 10.0002 ms, but 9.9767 ms. To get around this
> * would require using a different timing source.
You can also pretty trivially keep track of an error term so that the
clock is right on average:
#define CLK_HZ 1193200 /* or whatever */
#define ET_PRECISION 1000
#define ET_TIMER_TICKS CLK_HZ*ET_PRECISION/HZ
#define ET_PCSP_TICKS 64*ET_PRECISION
...
static long et=0;
...
et+=ET_PCSP_TICKS;
if(et>ET_TIMER_TICKS) {
et-=ET_TIMER_TICKS;
simulate_timer_tick();
}
This keeps track of the residual timing error to a few decimal places to
several decimal places and will get closer to HZ than even the current
code.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Mon Oct 23 2000 - 21:00:21 EST