Date: Fri, 11 Aug 1995 15:51:50 -0400 (EDT) From: Chuck Robey <chuckr@Glue.umd.edu> To: User Chris <chris@Janus.Druidix.COM> Cc: questions@freebsd.org Subject: Re: Serial speeds Message-ID: <Pine.SUN.3.91.950811154146.24590A-100000@cappuccino.eng.umd.edu> In-Reply-To: <199508111142.LAA00297@Janus.Druidix.COM>
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On Fri, 11 Aug 1995, User Chris wrote: > August 11, 1995 > Greetings, > I have a question about serial speeds on FreeBSD releases 2.0.5 > and 2.1 (upcoming?). I am currently running FreeBSD version 2.0 on a > 486. Works great! But I have had some minor problems with speeds on my > serial ports. Currently, I am running kermit over a slip link to netcom. > Unfortunately, I am doing this at 9600 bps since the operating system > doesn't recognize the request to run at either 14400 or 28800. I have > built kermit to recognize these speeds. > > So the question is this: > > Does the new (2.0.5 OR 2.1) release recognize the other speeds for higher > throughput? > > I know about running the port at as high a speed as possible (115K?) > and I tried it. But kermit and the OS are still not talking the same language. You've made some errors here. Those speeds of 14400 and 28800 are things you can't have and don't want. First thing, just because you've forced your version of kermit to swallow those numbers without burping, you won't get your uart to do those numbers; even if you had done that, you wouldn't want to. See, those 14400 and 28800 modems compress the data as they send it at those rates, so they need to be fed data much faster, and need to be able to get the data much faster too. Many folks set up 28800 modems to communicate at 115200 bps. Trick here is, just because a modem is sending data at 28800 to the far end modem, doesn't mean that it communicates with your computer at that rate; that doesn't happen. The modem senses the rate you communicate to it adaptively, and changes to suit your whim. That way, if the far end sends something to your that compresses real well, say loads of blank lines (maybe filled with spaces!), your modem will compress tat data, and send it much, much fater than 28800. What happens if the modem gets too darn good at compressing, and overruns your set data rate? Two leads in the RS-232 interface, called RTS/CTS, control how fast the transmit can go, by siwtching on and off the interface on sending. Two more leads help on receiving. Just recompile your kermit back to what it was to begin with, and set a data rate that's lots higher than your line rate. I don't personally like to use 115200, I use 38400, but nearly all the data I send has been compressed before it's stuffed into the modem to begin with (gzipped files). Give up trying to get 14400 and 28800 directly, you don't need it and won't miss it. ----------------------------+----------------------------------------------- Chuck Robey | Interests include any kind of voice or data chuckr@eng.umd.edu | communications topic, C programming, and Unix. 9120 Edmonston Ct #302 | Greenbelt, MD 20770 | I run Journey2 (Freebsd 2.0.5-snap-0726) and (301) 220-2114 | n3lxx (FreeBSD 2.0.5-snap-0622) -- Great! ----------------------------+-----------------------------------------------
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