Hello everybody,
some weeks ago, my student colleague Arni Ingimundarsson posed a question here. Thanks again for your answers, and I would like to continue this thread... We have been using PCs under the commercial RTOS RTTARGET (http://www.on-time.com) in Motion control. We have self-made ISA Timercards causing regular interrupts, and are getting Interrupt latency times of about 5µs. This was tested over a long time, and we got this result on three PCs of different age and power. Now we are trying out RTLinux. The tests were run on a Intel Celeron 300A with ISA timercard giving interrupt and the IRQ-handler sending one pulse to the Parallel-Port; that is one of the machines we tested RTTARGET on. RedHat 7.2 with RTLinux 3.1 on Kernel 2.4.4 and KDE. The latencies we got there were 14µs (ISA Interrupt source, Harddisk mounted but not used), and 10µs if we use the parallel port as the interrupt source. If we use the harddisk simultanously, the ISA latency time grows to 18µs (DMA mode on), and as high as 27 µs with DMA off. It's always only a few interrupt calls that are delayed so much, but we need to guarantee a latency... We are now trying to reduce the latency. Is it known what programs/tasks could be blocking interrupts? Wouldn't it be possible not to run those programs to guaranty shorter response time? If it is a hardware problem: Is it known which chips are making a mainboard good/bad? Can they be deactivated somehow? Can anybody recommend a board type / manufacturer? > From: Paolo Mantegazza <[EMAIL PROTECTED]> > Note that those 20 us are not so bad and are there to stay for ever. > They can disappear just if you can spoil your system of anything and use > very fast, likely non ISA, cards. What should I spoil in the system? Any ideas? > From: "Arne Linder" <[EMAIL PROTECTED]> > We're working with a similar equipment and we receive latencies about 4µs > on a quiet system. Worst-case-latencies slightly bigger that 10µs can not > be suppressed using a PC-based system, since PC mainboards are not > optimised for low latencies. How can I make my system "quiet"? Our Linux system does not need to be operating while the real-time task is running. > From: Der Herr Hofrat <[EMAIL PROTECTED]> > es hat nichts mit schneller zu tun - es liegt am ISA bus > man kann natuerlich ein DOS drauf setzen und einen einzigen task alufen > lassen der nur diesen einen interrupt bedient dann koennte es unter 20us > sein - was ich allerdings als worst case bezweifle fuer JEDES OS das > interrupts von anderen quellen zulaest wird es darueber sein But it worked with the ISA card and RTTARGET... There we had the keyboard and harddisk controller interrupts disabled and read the keyboard by polling. On another machine, it even works fine with those interrupts enabled. Thanks again for your answers. Any help is appreciated. Alexander Dipl.-Ing. Alexander Bähr TU Darmstadt, SRT Landgraf-Georg-Str. 4 64283 Darmstadt Germany TEL : 06151 162366 FAX : 06151 162613 [EMAIL PROTECTED] -- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] -- For more information on Real-Time Linux see: http://www.rtlinux.org/
