Date: Wed, 9 Apr 2003 15:47:28 +0200 From: Bernd Walter <ticso@cicely9.cicely.de> To: Harti Brandt <brandt@fokus.fraunhofer.de> Cc: ticso@cicely.de Subject: Re: realtime problem Message-ID: <20030409134727.GB95434@cicely9.cicely.de> In-Reply-To: <20030409144042.B901@beagle.fokus.fraunhofer.de> References: <20030409114957.GN83126@cicely9.cicely.de> <20030409144042.B901@beagle.fokus.fraunhofer.de>
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On Wed, Apr 09, 2003 at 02:45:07PM +0200, Harti Brandt wrote: > On Wed, 9 Apr 2003, Bernd Walter wrote: > BW>I need a realtime behavour in the (-current) kernel with 1ms > BW>resolution and a presision of 500us. > BW>I thought about these two ways: > BW>- use timeout(9), but it seems that on i386 we only have a > BW> resolution of 10ms. > BW> And I don't know of what presision quality I can expect. > BW> Can the resolution changed to 1ms as we have on alpha? > BW>- attach to the clock service routine. > BW> I asume the presision will be good enough. > BW> But how can I find out the resolution on a given hardware? > BW> > BW>What is the best way to solve the problem? > > You must change HZ by putting > > options HZ=2000 > > or whatever you want in your config file. > > You should also ensure, that you have no miibus ethernet cards in your > system, or comment out the relevant sections in dev/mii that periodically > call the status update stuff. > > I fact I have used a HZ=10000 machine to simulate a 120000 packets/sec > satellite link with good success (jitters are in the order of 300usecs). That's a hopefully information. Did you use a hardclock, timeout(9) or something else? > If you really mean 'real-time' with bounded times for interrupts and so > on, that will be much harder :-) See Terry's mail. Well it's wishfull to have non failures on my requirements, but if it does fail once it is detectable and it only costs a small amount of money - noone will die because of it. If I would need garantied 100% acuracy, then I would spend the money into a microcontroller to do the job. In fact I need it for the programming impulse on writing EPROMs and GALs. GALs are the devices which may need a 1ms programming impulse, but I don't know if there are really devices on the maket which use 1ms. EPROMS are not very sensible on the programming length. I really hate that available burners need DOS or Windows. -- B.Walter BWCT http://www.bwct.de ticso@bwct.de info@bwct.de
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