Date: Wed, 17 Dec 1997 14:46:08 +1030 From: Mike Smith <mike@smith.net.au> To: jak@cetlink.net (John Kelly) Cc: Mike Smith <mike@smith.net.au>, FreeBSD Hackers <hackers@FreeBSD.ORG> Subject: Re: 3com 3c509 card Message-ID: <199712170416.OAA01477@word.smith.net.au> In-Reply-To: Your message of "Wed, 17 Dec 1997 05:09:35 GMT." <349a59c3.99678713@mail.cetlink.net>
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> On Wed, 17 Dec 1997 14:04:26 +1030, Mike Smith <mike@smith.net.au> > wrote: > > >"AT Bus Design" (Edward Solari, Annabooks) > > BTW, I checked on getting that book and it seems to be no longer > available. Hmm. I'd better steal this copy then. If you're doing AT bus design work it's invaluable, if a bit terse. 8) > >Now, if you take into account just a little CPU overhead, interrupt > >cycle overhead, metadata overhead, you will quickly see that you're > >not going to route 4MB/sec aggregate traffic through anything on the ISA > >bus, period. > > I seem to have one 486 board running at 12 MHz ISA and clock doubled > 50/100MHz DX4-100 CPU will no apparent problems. This has reduced my > (measured) 8 bit I/O cycle time to 0.65 usec. I don't have a suitable > method for measuring the 16-bit cycle time, but I'm hoping for nearly > 4MB through this supercharged bus in 16-bit mode. You can expect that it will be half, based on the 6 clock/3 clock ratio, so about 325ns. > I'm only getting > about 700K per card, so I don't think I need a full 4MB anyway. I > might even be able to use five interfaces -- they won't be saturated > all the time. Yup. The other significant point is that you are routing, not bridging, so you are more concerned with through traffic than all-networks-aggregate. > >Personally, I'd recommend a 4-port Zynx card. > > I have a small truckload of SMC Ultras I need to use. That does constrain you somewhat. 8) mike
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