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
rocky@hpfcla.UUCP (02/23/86)
> Suppose it can execute 32,768 instructions per second. Now, suppose you > have a clock that counts in 1/65536ths of a second. Then, as far as you > are concerned, it's impossible to tell the clock is running that fast... Reminds me of the Nyquist sampling limit, stated a little differently: you can't accurately rebuild a signal from repetitive samples unless you sample at least twice the rate of the highest frequency contained in the signal. Just a throwback from years ago in analog land :-) Rocky "Where did the z-plane go" Craig hpfcla!rocky Hewlett-Packard Ft. Collins, Colorado
greg@utcsri.UUCP (Gregory Smith) (03/04/86)
In article <19900001@hpfcms.UUCP> rocky@hpfcla.UUCP writes: > >> Suppose it can execute 32,768 instructions per second. Now, suppose you >> have a clock that counts in 1/65536ths of a second. Then, as far as you >> are concerned, it's impossible to tell the clock is running that fast... > >Reminds me of the Nyquist sampling limit, stated a little differently: >you can't accurately rebuild a signal from repetitive samples unless >you sample at least twice the rate of the highest frequency contained >in the signal. Just a throwback from years ago in analog land :-) ^^^^^ ^^^ ?? What about digital audio / CD's / digital voice transmission / digital video etc...? >Rocky "Where did the z-plane go" Craig The z-plane is alive and well in a stereo store near you... -- ---------------------------------------------------------------------- Greg Smith University of Toronto ..!decvax!utzoo!utcsri!greg