Writing an Intelligent Serial Card Driver
auto-detects card and uses assigned IRQ for given address
presents DTR as function of open/close status
can send/receive data on all eight ports
works for login session from terminal problems
reception of character before transmitting first character is seen as a “hangup” by something; once first character is sent, reception works fine shortcomings
speed is fixed at 9600 baud
mode is fixed at 8 bits, No parity, 1 stop bit
modem status is ignored
wait-on-open doesn't wait
break is ignored
written for release 0.99p12 testing
haven't tested simultaneous send/receive
haven't tested simultaneous multi-port operation
And a few days later I added:
It appears the problem I reported for the Cyclodes driver is actually deeper within the kernel and appears with the other asynchronous drivers, i.e., it was there to begin with. Therefore I will ignore this problem for the moment, since the other ports work for all applications I know, and focus on getting the rest of the features right. First will be speed and line mode stuff, then the modem control.
I've dropped in the speed setting code and tested it at speeds up to 19200. Once I rig some kind of loop-back cable, I'll check higher speeds.
It now recognizes parity errors and break, the wait-on-open feature works, and multiple simultaneous sends and receives have been tested. The upgrade to kernel 1.1.8 is done and I'm working with some other folks on testing it more rigorously.
Checking back in my log one can see how I worked in spurts. I spent a bit over a week overall on this, mostly in day-long chunks. This was after a lot of hour-long periods reading the documentation.
So what did I gain and would I do it again?
I got a chance to pay my debt to the community. I got to play inside the kernel. I'm more confident that I can write drivers for this system and get them to work. I also got a mux board.
I'm not sure I would do it again. Not that it was that demanding, but it did take time. I don't think the gains would be as great the second time around. Still, if an interesting-enough device was offered to me, I'd be tempted.
Randolph Bentson can be reached at: (email@example.com)
- Readers' Choice Awards 2014
- Handling the workloads of the Future
- Android Candy: Google Keep
- diff -u: What's New in Kernel Development
- How Can We Get Business to Care about Freedom, Openness and Interoperability?
- Synchronize Your Life with ownCloud
- Days Between Dates?
- December 2014 Issue of Linux Journal: Readers' Choice
- Non-Linux FOSS: Don't Type All Those Words!