On 17 September 2010 09:16, Slavko Kocjancic <esla...@gmail.com> wrote:
> but with EMC that wil be like that 250,250,250,250, (new servo thread > calc), 245, 245, 245, 245,.... > I thinking to put stepgen in microcontroller as finding good PC with > lattency under 15us is not easy. The Intel Atom mini-ITX boards run at 8uS from a LiveCD installation, and cost $75 > So base period under 20uS is not likely > on PC but for $2 microcontroller the 5us is easy reach. In practice, it is very rarely a problem. Loaded stepper motors very rarely manage more than 2000rpm for reasons unrelated to drive pulse smoothness. (at 8x microstepping that is a 20uS pulse time). If you want finer granularity then both the Pico and Mesa systems offer that. The Mesa 7i43 plugs into a parallel port and offers 48 IO pins and hardware stepgen at (IIRC) MHz resolution. More expensive than your $2 uController at $79, but then it is already supported by EMC2 so will "Just Work". The same is true of the Pico PPMC cards, I believe, but I am less familiar with them. However, this still doesn't really help with the issue that seems to be bugging you, that the step rate only change every Servo Period. I am afraid that is not likely to be easy to change, as the floating point motion calculations take time, and can only be run in the slow thread. However, why not start off with your system running off the P-Port and see if there is a genuine issue? My axes max out at somewhere around 30mm/sec for reasons related to voltage and motor inductance, so <calculate> that is 720rpm from the motors, or a minimum step time of 100uS at x4 microstepping. I do actually have a 7i43 card so step timing granularity is not an issue and did not see any improvement in rapid speed compared to the p-port only system (I made the switch to get more IO pins) -- atp ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
