Date: Mon, 23 May 2016 13:44:55 -0700 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Andriy Gapon <avg@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: hpet as nmi watchdog Message-ID: <2056148.ZvOkyra82H@ralph.baldwin.cx> In-Reply-To: <56DEB97D.2010804@FreeBSD.org> References: <56DEB97D.2010804@FreeBSD.org>
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On Tuesday, March 08, 2016 01:37:33 PM Andriy Gapon wrote: > > I toyed a little bit with an idea of using a HPET timer as an NMI watchdog. > The idea is that a HPET timer is somehow configured to generate an NMI when it > fires. The timer normally would not fire, of course, as it is constantly being > reprogrammed to some future time as is the case for all watchdogs. > > I have written some proof of concept code using two approaches. One approach is > to use the "FSB" (MSI-like) mode of a HPET timer and program a corresponding FSB > data register (HPET_TIMER_FSB_VAL) with a value that sets NMI delivery mode > using the IO-APIC specification. The other approach is to use legacy interrupt > mode for the HPET timer and program a corresponding IO-APIC pin for NMI deliver > mode. > In both cases I haven't got a desired result - instead of an NMI a test system > gets reset when the timer fires. I wonder if this is a quirk of my old hardware > (HPET in AMD SB7xx, family 10h processor) or if my idea is a non-starter. This is an interesting idea. You could also use one of the other timers (8254, etc.) as a watchdog by setting the I/O APIC pin to NMI as well. It maybe that for the MSI case the chipset treats the NMI delivery mode as an error, hence the reset. :-/ -- John Baldwin
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