mmshah@athena.mit.edu (Milan M Shah) (12/17/90)
Hello. I have what I think is an 8259 programming question. I am trying to use a shareware comm IO package called comm_tp4 (comm_tp5) which seems to be very well written. I added simple xon xoff flow control to this. The program works fine just sending or receiving (I am using 9600 baud). However, when it tries to do both, it dies. It uses interrupt driver IO, and what seems to happen is that somehow I throw the 8259 (or the 8250) into a state where I receive no more interrupts. When I query the 8250 Interrupt Enable Register, it tells me that transmit and receive are enabled. My output buffer fills up, enables ints etc., and expects the outbuffer to clear sooner or later. But I cease to receive xmit or rcv ints, even though both should be occuring. Now here's the catch - the symptoms disappear and everything is just fine if I run the stuff under a command.com window (full screen or in a window) from withing windows! I ran a test for about a half hour, and it kept going. This seems to tell me that I am messing up the state of either the 8250 or the 8259, which windows detects and corrects for me. Any help would be appreciated! Thanks! Milan .