On 10/14/2016 09:50 PM, Chris Albertson wrote: > No, it would not get you to ns levels. > > > I've >> wanted to set this up on X86 through the parallel port for >> some time (since about 2002, in fact) but it would take some >> serious hacking on the PPMC driver. It looks like it might >> be easier with the uspace / rt-preempt kernel than with >> rtai. It would reduce latency/jitter to ns levels. >> Yes, actually, it WOULD. All the Pico Systems motion control boards can latch the position when the internal timer ticks. So, the position latching would be accurate down to the jitter of the crystal oscillator. (If multiple boards were used, then the latching would be accurate to the difference between the clocks on the different boards, so jitter would increase to 1 us, maximum, or 100ns if the encoders were updating at 10 MHz clock.) The master board sends the latch command on the parallel port bus to other boards on the bus, as well as the computer. The computer would have the luxury of responding before the next timer tick, nominally 1 ms. As long as the computer never took more than the timer period to complete its work, it would never cause ANY latency at all! The computer's updated velocity info would not become effective until the next timer tick.
Jon ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
