You will have to build an executable that will perform like this:
- Get permissions to use I/O address space, by calling kernel, with the command ioperm: eg ioperm( BASE, range ,1);
- Perform an out request instruction, to set the 0-5V voltage to the parallel port, eg outb( 1, BASE );
- Wait for enough time so that coffee gets ready. It would be nice if that time is read by looking at the command line.
- Then it will turn off the coffee-machine: outb( 0 , BASE );
- Before ending it should give back the paraller port with a ioperm( BASE, range, 0);
It would be nice if you had that program setuid, so that everybody can drink coffee!
Just read kernel hacker's guide, implement a device driver (it could even be user space I think). Please, compile it as a module, so that we won't need a kernel compile in every update. Then write:
echo cappuccino >/dev/coffee
And you will have a hot cup of coffee in 1 minute. Remember to give the right permission to /dev/coffee, depending on whether you want only root making coffee or not.
The advantage of this method is that it supports feedback from the coffee-machine by using the ACK of parallel port, so that smart coffee-machines could produce an interrupt.
Do it as homework.
If you have implemented the C programme (see above), you just have to write down a simple CGI script to turn ON and OFF the coffee-machine. You should write some nice webpages, explaining how to make coffee, and put them at an apache web server...