Date: Thu, 18 Dec 1997 13:10:03 +0000 (GMT) From: Andrew Gordon <arg@arg1.demon.co.uk> To: John Kelly <jak@cetlink.net> Cc: FreeBSD Hackers <hackers@FreeBSD.ORG> Subject: Re: 3com 3c509 card Message-ID: <Pine.BSF.3.91.971218130610.18688B-100000@server.arg.sj.co.uk> In-Reply-To: <34992437.46914518@mail.cetlink.net>
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On Thu, 18 Dec 1997, John Kelly wrote: > On Thu, 18 Dec 1997 01:15:50 +0000 (GMT), Andrew Gordon > <arg@arg1.demon.co.uk> wrote: > > >Note that a _standard_ cycle isn't the fastest possible cycle: 16-bit > >memory cycles have one wait state, but a board can generate 0 w/s > >cycles by holding NOWS* low. Since this is only applicable to memory > >cycles > > What prevents use of 0 WS for I/O cycles? > The ISA bus. The NOWS* signal is defined to apply only to memory cycles. This dates back to 286 machines with their main memory on the ISA bus: making the memory run at full speed was critical, dropping an extra cycle for I/O devices (many of which would insert even more wait states of their own) was not.
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