On 11/22/2014 10:39 PM, Gregg Eshelman wrote: > Isn't LPT latency pretty much a non-problem when using a > controller like the Pico instead of a cheap breakout board? No, actually it still is somewhat of a problem. A 100 us delay would be a serious problem for software step generation, as it might even cause the step generation thread to crash (overrun the whole thread period and the RT system may hang when it tries to start the thread while it is still running). 100 us delay will cause a 10% fluctuation in perceived velocity, assuming a 1 ms servo thread period. The Pico stepper board has no way to handle this, so it appears as though the speed just jumped 10% and it will try to adjust. The Pico PWM controller has velocity estimation using time stamps, and so it will be just a little more immune to this.
So, it all depends on the magnitude of the latency. 100 us delay on a 1 ms thread is not catastrophic, but it isn't GOOD, either! So, if the WORST latency that ever shows up is well under 100 us, then, YES, it is pretty much a "non-problem" on less critical machining tasks on low-speed machines. But, you have to QUANTIFY the latency before saying it is a "non-problem". Jon ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
