visjames@ubvmsd.cc.buffalo.edu (Larry James (WNYCUG)) (12/28/90)
I am looking for a good library of Interrupt driven communications routines
for C. I would like source code if possable. They need to be extreamly fast
as they will be used on a Multitasking XT at 38,400 bps. Can anyone help me
find some so I don't have to write my own?
Thanks in advace.williams@umaxc.weeg.uiowa.edu (Kent Williams) (12/29/90)
38,400 BPS is too fast on an XT unless you do a hard polling loop in
assembly language.
38,400 BPS = 3,840 CPS (at 8 bits per byte). That means an interrupt
roughly every 275 microseconds. You have roughly one instruction per micro-
second on an XT (and that's being generous). I would estimate you couldn't
do a bare bones interrupt service in under 50 instructions, so you would tie
up the CPU 1/5 of the time in interrupt services for the serial port. Then,
consider how many instructions it takes to effect a task switch from the timer
tick interrupt. What do you get? Missed serial port interrupts!
--
Kent Williams --- williams@umaxc.weeg.uiowa.edu
"'Is this heaven?' --- 'No, this is Iowa'" - from the movie "Field of Dreams"
"This isn't heaven, ... this is Cleveland" - Harry Allard, in "The Stupids Die"