Q: How can I have the cube act as a server for a certain application, and accept requests from a modem?
A: The goal is to have the application software be able to answer and respond to incoming calls (via a modem). To do so, have the application software open /dev/ttyda (or /dev/ttydb); this open will block until "Carrier Detect" is asserted by the modem connected to the 'a' ('b') mini-din serial port. Carrier detect is the modem signal that indicates that a dial-up connection has been made. When the open returns, the application can then begin communicating with the remote user. When the user hangs-up, carrier detect will be deasserted by the modem, that will cause Mach to send a "SIGHUP" signal to the application; the application should then close /dev/ttyda. The application can prepare to receive another user connection by attempting another open of /dev/ttyda. To implement this will require some amount of C software in the application to properly configure the line and implement the SIGHUP signal handler. Be especially careful when wiring the cable to the modem (see zs(4) man page). You will also want to insure that /dev/ttyda or /dev/ttya is not referenced in the /etc/ttys file.
If you want to use an outgoing connection, then consider "tip". "tip" is a program that can drive an auto-dialing modem for outgoing calls. See the man page for tip and zs to understand its configuration.
On 68040-based systems, RTS/CTS flow control is supported through /dev/ttydfa and /dev/ttydfb.
