Several years ago, I was asked to evaluate the Real Time O/S that Intel was offering for sale as a project in an electrical engineering course. Interrupt latencies and servicing times are very important in real time control, so I evaluated the parallel port. As I recall, I output a signal to one pin on the parallel port and then sent out a digital output to a point where I could measure it with an oscilloscope after receipt of the interrupt in my test program. I used the oscilloscope to measure the time from the first signal to its recognition by my program. I don't remember the exact results, but I do remember that the latencies were highly variable. Intel subsequently sold the real time O/S, and I have not seen it for sale since.
Charles Elliott -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Rob Sent: Sunday, February 23, 2014 12:36 PM To: [email protected] Subject: Re: [ntp:questions] Atom PPS with parallel port David Lord <[email protected]> wrote: > Rob wrote: >> I would like to use the Atom driver (22) on a Linux system with a >> parallel port. It is not clear to me from the scattered info I have >> found on internet if this is going to work. >> >> Using a modern Linux kernel with the PPS module, is it possible to >> symlink /dev/pps0 to a parallel port device and then connect the PPS >> signal to the ACK input (pin 10)? >> >> If not, what else is required to get this working? >> >> Examples always refer to the use of a serial port DCD input, but for >> best accuracy (in the microsecond range) I think the parallel port is >> better. >> (no RS232 drivers/receivers, no funny UART that may delay interrupts) >> >> Any other suggestions for an accurate PPS input? > > On NetBSD with stock ntpd, pre 2010, I did comparisons of pps from > Sure GPS with output from dcd at ttl level vs the "serial" dcd but > didn't really see any consistent difference. Did you try the parallel port? I am interested not only in jitter but also in any constant offset between the PPS pulses and system time on different systems (possibly using different makes of serial card). 4-6 us would be good enough for my purpose, but it would not be good when one system had a 10us offset because of a propagation delay in a linedriver/receiver. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
