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Re: current kernel on amd64 crashes
On Thu, Jan 10, 2008 at 02:55:52PM +0100, Manuel Bouyer wrote:
> Ha OK, it's on a HVM guest.
> I guess the relevant NetBSD code is x86/isa/clock.c
> Could it be this change ?
> - low = inb(IO_TIMER1 + TIMER_CNTR0);
> - high = inb(IO_TIMER1 + TIMER_CNTR0);
> - count = rtclock_tval - ((high << 8) | low);
> + /* insb to make the read atomic */
> + insb(IO_TIMER1+TIMER_CNTR0, &rdval, 2);
> + count = rtclock_tval - rdval;
I don't know, but I also have no reason to believe that the comment (and
hence the modified code) is correct.
In order to get a consistent view of the counter, you have to latch it.
Any other attempted procedure (eg reading high-low-high) is doomed to
failure because some systems don't even report consitent byte values
when unlatched. (and soeme just return junk occaisionally).
David Laight: david%l8s.co.uk@localhost
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