Thanks Andy and Jon, I'm beginning to understand. Regards Andy -------------------------------------------------- From: "Jon Elson" <el...@pico-systems.com> Sent: Saturday, October 23, 2010 7:14 PM To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Subject: Re: [Emc-users] 7i43 or 5i20
> Andy Pugh wrote: >> Possibly. I have read somewhere that a sane (200uS) servo-thread >> _execution_ period is only enough time to shift 50 bytes through a >> parallel port. That is potentially limiting, but has not been a >> problem I have noticed with my 4-axis machine. The software stepgens >> running in the base thread and twiddling pins individually are >> effectively shifting one word per thread cycle. >> > At first I was going to take major exception to your numbers, but if > your servo loop has > to read position, compute PID, etc. and then write velocity out to the > device, > actually, you may be just about right! Using a PCI parallel port in EPP > mode, > 200 us should allow up to 250 bytes or so to be transferred, but that > would take up > the entire SERVO_PERIOD. You have to leave some slack for timing > variation, > and also for computation. So, the 50-byte figure might be quite close. > > For my USC board, for instance, there are 4 axes, with 3 bytes of > position and > 3 bytes of velocity for each. Plus a little digital I/O. So, it reads > 14 bytes and write > 13, plus setup and control overhead. Total of about 35 I/O operations > per servo > cycle. You could easily run a 10 KHz servo cycle with 4 axes, or 5 KHz > with 8 > axes on a modern CPU and PCI parport. > > Jon > > ------------------------------------------------------------------------------ > Nokia and AT&T present the 2010 Calling All Innovators-North America > contest > Create new apps & games for the Nokia N8 for consumers in U.S. and Canada > $10 million total in prizes - $4M cash, 500 devices, nearly $6M in > marketing > Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store > http://p.sf.net/sfu/nokia-dev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
