I'm also doing quasi real time work with OSX. I've developed a time
data server for OS9 that I'm porting to OS X 10.3/Xcode. I've had good
success using the POSIX pthreads API combined with termios for
real-time handling of a serial port connected GPS time-code generator
(Ashtech G12). The time code, output at 20 Hz rate, is acquired from
the serial port. triggering the sampling of sensor data. The time
stamped data is moved to a UDP packet and transmitted. Each stage is
handled by a separate pthread that has priority set depending on
timing requirements. I verified the timing using an oscilloscope
connected to the serial and ethernet ports while network and gui were
very active. The jitter can be reduced considerably by adjusting the
real-time parameters. This is all done outside of the kernel!
(meaning: easy to code and debug)
The OS X Mach kernel has an good API for setting thread priority from a
user program. See:
It includes the API to set priorities from a user program.
Good Luck
Michael Goldin
Senior Development Engineer
Scripps Institution of Oceanography
University of California San Diego
phone: (858) 534-3863
email: email@hidden
On Apr 9, 2004, at 7:48 AM, W. R. Wing wrote:
Can someone point me in the right direction to look for documentation
on near real-time work in OS X? I'd like to be able to apply VERY
precise time stamps to tcp packets, and need to minimize jitter
associated with other time sharing and interrupt activity. Lots of
folks here have experience doing this sort of thing in Linux (with
various degrees of success), and in a general way I'd like to know
whether or nor OS X lends itself to being able to do this sort of
thing better or worse than Linux does. If it just isn't practical, no
point in beating some poor post-doc's head against the wall, but if it
can do the job much better than Linux, it would be another minor
victory.
If there is a better list to post to - I apologize (and would ask for
a pointer).
Thanks,
Bill
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