Re: ISA bus and SLOW_DOWN_IO

Eric.Schenk@dna.lth.se
Mon, 26 May 1997 17:30:13 +0200

"Richard B. Johnson" <root@analogic.com> writes:
>The problem is that we need 300 to 600 ns! BogoMips isn't going to do it.
>It is true that we are back to the clock-speeds of the uP, but the RAM
>stack access times dominate. Anything greater than 600 nanoseconds wastes
>time. Anything less than 300 may result in the glitches. This does not
>have to be very accurate.

But we should be able to use the same principle. On at 33Mhz 486 we
get about 20 clock ticks in 600ns. When we are talking a 200Mhz Pentium
we are looking at 120 clock ticks. We should be able to calabrate a small
bit of loop code so that it takes about 600ns on pretty much anything
that will run Linux. Say use a 16Mhz 386 as the worst case. I assume
that even that slow a processor can make it once around a countdown loop
in 10 clock ticks.

(Or did one of slip a decimal somewhere here?)

-- 
Eric Schenk                               www: http://www.dna.lth.se/~erics
Dept. of Comp. Sci., Lund University          email: Eric.Schenk@dna.lth.se
Box 118, S-221 00 LUND, Sweden   fax: +46-46 13 10 21  ph: +46-46 222 96 38