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

[yodaiken@chelm.cs.nmt.edu]

2us-3us is typical case - not worst. The bottom half invocations of cli/sti
don't do anything to us.


On Wed, Oct 07, 1998 at 10:20:07AM -0500, Manoj Apte wrote:
> 
> 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
> > 

-- 

---------------------------------
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

--- [rtl] ---
To unsubscribe:
echo "unsubscribe rtl" | mail majordomo@rtlinux.cs.nmt.edu OR
echo "unsubscribe rtl <Your_email>" | mail majordomo@rtlinux.cs.nmt.edu
----
For more information on Real-Time Linux see:
http://www.rtlinux.org/~rtlinux/