Date: Tue, 11 Jul 1995 19:51:55 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: babkin@hq.icb.chel.su (Serge A. Babkin) Cc: dennis@et.htp.com, md@dcs.qmw.ac.uk, freebsd-hackers@freebsd.org Subject: Re: Wanted: 100bT EISA ethernet recommendation Message-ID: <199507120251.TAA16930@gndrsh.aac.dev.com> In-Reply-To: <199507120215.IAA17281@hq.icb.chel.su> from "Serge A. Babkin" at Jul 12, 95 08:15:15 am
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>
> > >EISA bus speed is 33Mb per sec which is 3.3 times faster than 100bT
> > >ethernet, so speed is not a problem.
> > >
> > You're arguing against yourself here. I hope that EISA is more than 33mbs
> > since I get 40mbs on my 10mhz ISA bus. But I was pretty sure that 100bT was
> ^^^^^ ^^
> ISA bus takes two cycles per transfer and transfers 2 bytes. Normal clock
> speed is 16MHz, it gives 8M transfers per second and 16MBs. Perhaps your
> bus gives 10M transfers per second (I don't believe that you have slowed
> your bus :-) ) and 20MBs. But not 40.
>
> > 100mbs.....
> ^^^^^^
> Yes, 100 Mega bits (Mbs) per second, not Bytes (MBs) :-)
> ^^^^
Could I please ask arm chair design engineers to please stop trying to
correct incorrect information with more incorrect information...
a) There is not a spec for ISA bclk frequence, it is typeically 6 to 12MHz
in range, most common values being beteen 6 and 8.333MHz
b) It takes 4 bclk ticks for an IO data read or data write, plus the
intercycle bus recovery time of 0 to 8 bclk's, typical being 5 bclks.
c) As soom one else pointed out (and I am guilty of this too by following
dennis's lead without catching my self. mbs is milli-bit-second and
pretty meaningless, belived he wanted Mb/s wish is Mega-bit per second.
10mhz != 10MHz, 10 Mega Hertz is what is correct. 16Mega-bit-second,
no, you mean 16Mb/s, 16 Mega bits/second. This is a technical fourm,
let us please use technical abbreviations correctly.
d) Theoretical maxiumum ISA bus transfer rate given a bclk of 10MHz and
a bus recovery time of 0 bclks is 5MB/s or 40Mb/s, exactly what dennis
reported and why I did not flag those numbers at all. I did flag
the EISA rate, which theory says for bclk of 8.33MHz and using burst
mode bus master DMA cycles (Which Dennis is also right about was not
in the very early EISA spec) is 33MB/s or 264Mb/s.
Thank you,
--
Rod Grimes rgrimes@gndrsh.aac.dev.com
Accurate Automation Company Reliable computers for FreeBSD
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