[Soekris] 4801 and FreeBSD -current

[Luigi Rizzo]

On Wed, Aug 06, 2003 at 06:54:02PM +0200, Poul-Henning Kamp wrote:
> In message <20030806094040.B62011 at xorpc.icir.org>, Luigi Rizzo writes:
> >On Wed, Aug 06, 2003 at 03:47:39PM +0200, Poul-Henning Kamp wrote:
> >> 
> >> At least under FreeBSD -current, but probably also -stable, the TSC
> >> is no good for timekeeping.
> >
> >why is that ?
> 
> It seems to be one of the "stop TSC while halted" things.
> 
> In addition they have the oddest bug I've seen on a TSC for a long time:

oh sorry, is this specific to the CPU used on the 4801 then ?
	
	cheers
	luigi

> 2.17 Time Stamp Counter rollover
> 
> Description:
> 	The upper 32 bits of the Time Stamp Counter (TSC) increment
> 	three core clocks before the lower 32 bits rollover. If the
> 	TSC is read and EAX is FFFFFFFDh, FFFFFFFEh, or FFFFFFFFh,
> 	then EDX will have incremented.
> 
> Implications:
> 	The TSC cannot be read reliably.
> 
> Resolution:
> 	1) Use the TSC as a 32-bit counter.
> 	2) When the TSC is read and EAX equals FFFFFFFDh, FFFFFFFEh,
> 	   or FFFFFFFFh, then decrement the EDX value by 1.
> 
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at 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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