Date: Sat, 13 Jul 1996 22:19:01 -0400 (EDT) From: Henry Spencer <henry@zoo.toronto.edu> To: "Jacob M. Parnas" <jparnas@jparnas.cybercom.net> Cc: hardware@freebsd.org, bsdi-users@bsdi.com Subject: Re: cable vs. ISDN Message-ID: <Pine.3.89.9607132250.A239-0100000@zoo.toronto.edu> In-Reply-To: <199607132102.RAA10473@jparnas.cybercom.net>
next in thread | previous in thread | raw e-mail | index | archive | help
> ...Modems seem to have like a 2-4 Kbyte FIFO, even
> inexpensive ones, made back in the mid 80's. Why, except for poor design,
> weren't they at least an option on the computer side. (1 byte was normal, 16
> was "buffered")
The modems weren't single-chip devices. They were a boardful of
electronics, typically including at least one microprocessor. (At one
point, the modem I was using had considerably more computing power than
the computer it was connected to.) In fact there was no actual FIFO on
them -- the microprocessor had a few KB of RAM, and used that for data
buffering among other things.
> I'm also confused as to why building FIFO's is difficult or complicated.
> I remember we built one as a project in my first hardware course back in
> 1982-1983 and nobody found it hard (it was a beginning minor project nobody
> seemed to have problems with.
It's easy enough to do, but doing it on a chip does eat a fair bit of space.
> >Only when you start running a real operating system (or a kludged imitation
> >thereof :-)) do you start to care about buffering.
>
> True, but even machines like Sun Sparc 2's or IBM RT's which only ran Unix
> had small FIFO's. And they only ran Unix.
However, if you look inside them you will usually find that their serial-I/O
chips are off-the-shelf commercial designs built for other markets.
Henry Spencer
henry@zoo.toronto.edu
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.3.89.9607132250.A239-0100000>