Re: [rtl] Stability Problems while generating 1KHz signals

[Manoj Apte <manoj@ERC.MsState.Edu>]

Its not just the 8253 access time (which IS significant .. i measured it
to be about 2us-3us per write), I did the same test using the Realtime
Clock (RTC) giving me an interrupt at a regular frequency. and same kinda
spikes showup.

The reason i got a lil more convinced onthe bottom half argument is that,
if one looks thru the irq0 handler code, at many places it does a cli/sti
(4 actually) so I tend to believe this could be the cause. Though.. the
20us still bothers me.. since the duration of those cli's arent THAT big.
 

On Wed, 7 Oct 1998 yodaiken@chelm.cs.nmt.edu wrote:

> 
> What you are seeing mostly is the cost of access to the 8253/4 - about 18us.
> What chipset are you running? Until recently, the apic timer was not
> accessible in uniprocessor systems. The SMP version of rtl uses the apic
> timers and gets much lower jitter. 
> 
> > I know i am using an old version.. didnt muster the enthu to upgrade
> > linux.. and aint sure if the newer rtlinuxes work on 2.0.30
> 
> The new scheduler is slightly tighter on some measurements.
> 
> 
> -- 
> 
> ---------------------------------
> Victor Yodaiken
> Department of Computer Science
> New Mexico Institute of Mining and Technology
> Socorro NM 87801
> Homepage		http://www.cs.nmt.edu/~yodaiken
> PowerPC Linux page	http://linuxppc.cs.nmt.edu
> Real-Time Page		http://rtlinux.org
> 

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