Date: Wed, 11 Oct 1995 12:45:42 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: bde@zeta.org.au (Bruce Evans) Cc: hackers@freebsd.org, msmith@atrad.adelaide.edu.au Subject: Re: non-sio UART driver Message-ID: <199510110315.MAA13211@genesis.atrad.adelaide.edu.au> In-Reply-To: <199510101009.UAA15689@godzilla.zeta.org.au> from "Bruce Evans" at Oct 10, 95 08:09:36 pm
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Bruce Evans stands accused of saying: > > > As I dribbled a little while ago, I need to talk to a multidrop serial bus > >using a standard serial port. > > What's a multidrop serial bus? Ok ok, so "multidrop bus" is a bit of a tautology. I guess I should have said 2-wire RS-485. > >The nature of the protocol and interface mechanism for the bus tend to > >indicate to me that I don't want to use the sio driver and hack on that, > >but perhaps to make a copy and cut it severely down to size. > > If you need to do any normal serial i/o to a 16x50 then I suggest adding > to sio. It's not terribly "normal", in that writes to the bus are meant to be sort-of atomic transactions. (Being 2-wire, you go from listen to drive by raising DTR, write your packet, and then as soon as the last character's finished, you drop DTR again to listen for the response.) > If there are only protocol differences, then use a line discipline. Slip > and ppp are good examples. This doesn't sound unreasonable, although it wasn't clear whether you could guarantee that you'd get a whole packet passed down to the sio driver at once. Going on and off the bus inside a packet isn't viable, as you generate glitches that can throw the listener off. > Bruce > -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] My car has "demand start" -Terry Lambert UNIX: live FreeBSD or die! [[
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