On modern motherboards the parallel port is no longer ISA, but is on some Intel invented, and poorly documented, X-bus.
On Tue, Sep 17, 2002 at 09:24:10AM +0100, Iwo Mergler wrote: > Michel Julier wrote: > > > > Hello, > > > > SPEED: > > I have a concern about the speed of transfers from IO ports (on an ISA > > bus) to the memory. I am using and insb() instruction (that is "REP; > > INSB" in assembly) in an rtlinux real-time thread in the kernel. > > According to the specs for 386, I expect to spend 2 cycles for "REP" and > > 9 cycles for "INSB" (386 protected mode at highest permission level). > > Forget it. Those numbers are for the processor, not for ISA. ISA runs > at 8MHz with rather long and ineffective bus cycles. Every time you do > an I/O access, your helpful chipset will slow the processor down to > that speed. My old 286, which has a 12MHz Processor & bus is a lot > faster > than my new Athlon 1600. Funny enough, this behaviour is generic for > I/O, so even I/O on the PCI bus works at that speed. > > >From my experience I/O takes 1us per access. This is constant enough > accross different PCs, so the Linux kernel uses it for timing. > > > > > However, using a scope, I find that each byte takes 2µs (on a > > Pentium-MMX at 133 MHz) or 3µs (on a DIMM-PC: 386SX at 40MHz) to arrive. > > The read cycle itself (that is /IOR=0) takes about 500ns (already quite > > long), and I really cannot understand what does the processor the rest > > of the time. > > > > Does anyone have any idea? Is it just normal, or can I try something > > else? What really puzzles me is that I know some systems that transfer > > up to 1MB/s on the parallel port. Each byte needs at least 2 IO > > operations, so how is it possible? > > I have heard that rumour myself, but could not reproduce it. You can > get that speed using ECP and DMA but with software control you can only > reach about 500K/s. EPP will get you close to 1M/s with a very fast EPP > device. > > Kind regards, > > Iwo > > -- > Iwo Mergler, Navigation Systems, > Philips Semiconductors - Systems Laboratory (Southampton). > Tel: +44 (0)2380 31 2646 (Direct Dial) Fax: +44 (0)2380 31 6304 > mailto:[EMAIL PROTECTED] > _______________________________________________ > Rtl mailing list > [EMAIL PROTECTED] > http://www2.fsmlabs.com/mailman/listinfo.cgi/rtl -- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com _______________________________________________ Rtl mailing list [EMAIL PROTECTED] http://www2.fsmlabs.com/mailman/listinfo.cgi/rtl
