Re: [uCsimm] Problems with RTS and CTS in uCsimm

From: Vladimir Gurevich (
Date: Wed Jan 03 2001 - 14:39:56 EST

Hello Asier,

CTS/RTS signals are used for flow control on RS-232. I.e if you
send too much data to the modem, it will de-assert CTS and re-assert
it after it frees up some of its internal buffers. If your system is
too slow and the modem receives too much data from the outside, uCsimm
might de-assert RTS so that the modem could then apply backpressure to
the far end.

>From your description I don't think you have any flowcontrol problems,
thus it probably has nothing to do with CTS/RTS.

> 2.-I use telnet as a login, i don't use ttyS0 because i have connected
> a modem in, and i have changed /etc/inittab file for not use ttyS0 as login.
> 3.-I type agetty -w -I 'AT\015' 9600 ttyS0 to start the modem
> connected on port ttyS0.

Well, first of all, agetty is supposed to run only ONCE. It should
be respawned afterwards. That's why it is in /etc/inittab.

Second, make sure, your modem is configured in such a way that it does not
echo the AT commands.

Third, and most important. To be able to support dialin modem connections
you have to have DCD pin on your RS-232, but M68EZ328 UART does not provide
it. This should cause some problems with agetty. E.g. if you configure the
modem as I told you before, you'll probably need to hit <return> after
connect and then you'll get "Password: " prompt instead of "login: "
and stuff like that.

Alternatively, you should use a much more sophisticated getty, like mgetty,
which does not rely on the RS-232 I/O being blocked until DCD is asserted.
But you'll need to port it yourself.

Happy hacking,

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