Jon, You suggest that the PC would request the registers from the IO board and the IO board would respond with the requested registers. How much delay, jitter, latency,... is acceptable?
The processor could send a new command every servo cycle. On receipt of the command, the IO board could then send the current registers to the PC AND process the command. The PC would use those registers to compute the next command. There will always be a delay between reading the registers and generating a new command. Is the delay using this scheme too long? Can the software compensate for the delay? Given the current velocity and the time delay, we could compute a projected position. Given the velocity, acceleration, and time delay, we could do even better. This approach would save one packet. More importantly, the PID calculation could take more time. In fact, it could use the essentially the entire servo cycle time. That would let us increase the servo rate. I think of this as overlapping the operation of the PC and the IO board. Does it make sense? Ken [EMAIL PROTECTED] Mark Kenny Products Company, LLC 55 Main Street Voice: (888)ISO-SEVO (888)476-7386 Newtown, CT 06470 Fax: (203)426-9138 http://www.MarkKenny.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Jon Elson Sent: Saturday, October 27, 2007 7:16 PM To: Enhanced Machine Controller (EMC) Subject: Re: [Emc-users] Ethernet I/O Brian Michalk wrote: > I've done a bit of programming and circuit board design with Silicon > Laboratories 8051 chips. They have an ethernet developers kit complete > with schematics. > http://www.silabs.com/tgwWebApp/public/web_content/products/Microcontrollers /en/EthernetDK.htm > > > I have not priced the components, but a board should cost less than $20 > each. The 8051 is not a good choice for real time control of motors at high precision. I suspect that an 8051-based interface might just barely be able to keep up with a 1 KHz servo update rate (2000 packets/second received, 1000 packets/sec sent back to PC). I'm hoping to be able to turn up the servo update rate quite a bit with this system. The chip that I've been looking at has a 10/100 Mbit/sec ethernet MAC on chip, with DMA transfer to dedicated on-chip RAM. It is based on the 32-bit ARM7 processor, which is likely to be hundreds of times faster at handling the ethernet protocol. Even at 1 KHz servo rate, it would have to receive a request from the PC, decode it, perform the requested register reading and then build a packet to send back to the PC. The PC would take 50 us or so as do the PID calculations and then send a velocity command packet to the device. It would be good to handle each request in maybe 100 us or so. I have great doubts that an 8051 could process the protocol stack and do the I/O in 25 or so instructions. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
