Date: Wed, 5 Apr 1995 23:50:21 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: gurney_j@efn.org (John-Mark Gurney) Cc: terry@cs.weber.edu, matt@lkg.dec.com, vernick@cs.sunysb.edu, freebsd-hackers@FreeBSD.org Subject: Re: PCI/EISA/ISA performance Message-ID: <199504060650.XAA02656@gndrsh.aac.dev.com> In-Reply-To: <Pine.SUN.3.91.950405232030.16601D-100000@haus.efn.org> from "John-Mark Gurney" at Apr 5, 95 11:22:32 pm
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> > On Tue, 4 Apr 1995, Rodney W. Grimes wrote: > > [...] > > > ISA does not have a specified clock frequency, I have seen it running > > as fast as 16Mhz. Most boards die above 10Mhz, but some of the more > > specialized industrial applications boards are spec'd upto 12 or 16Mhz. > > actually... I think that I am currently running my isa bus at 16mhz... I > think for a while I was tring to run the bus at 20... but it was falling > over and wouldn't boot... and this is with ne2000 clone cards... and > other generic cards... I suspect you are off by a factor of 2, I haven't seen a ``generic'' card of any sort that would run at 12Mhz, let alone 16Mhz. IDE controllers are famous for falling over above 10Mhz (ever done a transmission line simulation of an unterminated ribbon cable :-)). If your basing this on a CPUCLK/N value and you think CPUCLK is 66 Mhz because that is what the crystal is you have made a mistake. Can you tell me what CPU chip you have, what speed is it, and what your BIOS says about ISA bus clock speed settings (list all the valid values). Also what BIOS is it? AMI, Pheonix, AWARD or someone else. Realize a 486DX33, 486DX2/66 and 486DX4/100** all run with a CPUCLK of 33 Mhz. A 486DX25, 486DX2/50 and 486DX4/75 all run with a CPUCLK of 25 Mhz. A 486DX50 runs with a CPUCLK of 50Mhz. ** The 486DX4/100 can also be run with a CPUCLK of 50Mhz if the motherboard supports the 1:2 bus/core ratio jumper. Pentium processors are similiar except the CPUCLK values are 50Mhz, 60Mhz and 66Mhz. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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