Date: Sun, 11 May 1997 12:42:24 +0100 From: Brian Somers <brian@awfulhak.org> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: hackers@FreeBSD.ORG Subject: Re: sio flow control problems with 2.2? Message-ID: <199705111142.MAA14168@awfulhak.demon.co.uk> In-Reply-To: Your message of "Sat, 10 May 1997 16:38:35 %2B0200." <199705101438.QAA19811@labinfo.iet.unipi.it>
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> Hi, > > I am a bit afraid to ask since this might be a configuration problem > on my side, but after a week of tests and tens of wasted calls I > think I need some advice. > > Since when I upgraded our ppp server to a P6-200 running FreeBSD > 2.2.1R, using a 28.8 modem (which reports 24000 bps at connect) I > am having problems with modem flow control. I am using the same > modems and serial port setup as on our previous server (a P5-133 > w/ FreeBSD 2.1) and client (a P5-133, w/ 2.1 and 2.2, both of which > worked), which has been working for months with iijppp. > > But now, even if, on the client, I start ppp, log into the server > (using mgetty), and then start elm, the output is a total mess, I have > missing lines, etc. as if flow control were not working. The only way > to make things work is to reduce the speed to 9600 at the server side > (and still... I suspect it just happens to work..). PPP fails with > packets longer than ~750 bytes. Strange. If you've got a tcp connection (on ppp), tcp should checksum and serialise everything. If there are flow control problems, they should effectively freeze the link. > On both sides, cuaa1 is set with -clocal crtscts, the internal > modems are (apparently) set properly (AT&K3 or AT\Q3, "enable > RTS/CTS flow control"), as in the past, and they are recognised as > 16550 at boot. There are options to allow allow XON/XOFF in ppps config (I've never tested them, I just noticed them when I was there for another reason), but the default is hardware. With pppd, I believe you need to specifically say crtscts in the options file (or on the command line). > What I suspect is that the new machine might be too fast in > pumping data to the modem, and for some reason it might miss the > handshake thus overflowing the receiver. It might be a broken modem > or something wrong in the sio code, has anyone suggestions where > to look at ? It's theoretically impossible to give the modem too much data - the next character is only sent on receipt of an interrupt (maybe you've got something else causing interrupts ?) that says the transmit buffer is empty. > Thanks > Luigi > -----------------------------+-------------------------------------- > Luigi Rizzo | Dip. di Ingegneria dell'Informazione > email: luigi@iet.unipi.it | Universita' di Pisa > tel: +39-50-568533 | via Diotisalvi 2, 56126 PISA (Italy) > fax: +39-50-568522 | http://www.iet.unipi.it/~luigi/ > _____________________________|______________________________________ I think your first step should be to prove you can log in using kermit or some such and see that flow control works there. Then you can put ppp and tcp/ip on top. -- Brian <brian@awfulhak.org>, <brian@freebsd.org> <http://www.awfulhak.org>; Don't _EVER_ lose your sense of humour....
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