Date: Mon, 18 Feb 2002 21:48:18 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Mike Smith <msmith@hub.freebsd.org>, John Polstra <jdp@polstra.com>, hackers@FreeBSD.ORG Subject: Re: ACPI timecounter tests original fast version vs masked version Message-ID: <45878.1014065298@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 18 Feb 2002 12:40:59 PST." <200202182040.g1IKex936264@apollo.backplane.com>
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In message <200202182040.g1IKex936264@apollo.backplane.com>, Matthew Dillon wri
tes:
> In anycase, I think this is reasonable especially if we explicitly
> use the fast code for those chipsets known to be good. I would like
> to commit it. It can handle *ANY* sort of ripple or fast-carry breakage,
> really any type of breakage since it looks for two identical samples
> after masking rather then using an inequality.
My only worry here is laptops.
If my laptop is connected to the wall-power when it boots it comes
up at full CPU speed during the probe and mask determination.
Then I unplug it and the CPU speed drops by a large factor and
suddenly the mask is too tight for the CPU to get two samples.
I think we need an approach where we loosen the mask at runtime if
some significant number of iterations fail to get a count may be
needed:
#define N 25
static unsigned mask = 0xfffffffe;
for (;;) {
for (i = 0; i < N; i++) {
c = READ_TIMER & mask;
d = READ_TIMER & mask;
if (c == d)
return(d);
}
printf("Adjusting mask to %08x\n", mask);
mask <<= 1;
}
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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