campbell@sauron.UUCP (Mark Campbell) (02/21/86)
One last (I hope) word about this stuff...concerning context switches and timers with respect to timing delays inherent in some devices. It really doesn't make a lot of sense to talk about setting up a timer to implement these delays, even if the delay were much longer than ~2us. The problem is not only the context switching times others have mentioned, but the overhead associated with setting up some type of critical region around the device in question. With two or more processes attempting to access the device, the "sleep"/"wakeup" scheme just won't cut it. This isn't speculation; I recently had to build some tightly-coupled interprocessor communication code that required that a new state be added to Unix for just this reason. It wasn't a pretty sight... -- Mark Campbell Phone: (803)-791-6697 E-Mail: !ncsu!ncrcae!sauron!campbell