Yes, you are right and it is nice that you point to the isochronous transfers, but as a Microsoft standard, USB has had poor latency. It is not known to me how are any recent latency tests...
On 4/23/07, Kenneth Lerman <[EMAIL PROTECTED]> wrote: > Mario, > > It is my understanding that usb supports isochronous transfers with > guaranteed access to usb bandwidth and bounded latency. That would clearly > support realtime actions. > > The bandwidth is clearly high enough to support our requirements. It is not > clear (to me) whether usb would meet our latency requirements. > > 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 Mario. > Sent: Monday, April 23, 2007 8:25 AM > To: EMC developers > Subject: Re: [Emc-developers] DIY USB interface > > > Kenneth... USB does not support realtime actions, so it is no direct > replacement. > > But I still see some advantages in the realtime core. And that is > precise timing. > > Easiest way how to find out how EMC works is to install it and find > out. Maybe only running live CD might help. Source codes and some > documentation is in there. There are many products - PCI and IDE cards > supported and used in EMC. How this might be edited/changed to use > with some USB device I don't know precisely. I will be returning to > work with EMC in a month or so, until then I have to do much less > interesting work/job. > > On 4/23/07, Kenneth Lerman <[EMAIL PROTECTED]> wrote: > > The place I see for USB in EMC is to replace the printer port solutions. > The > > advantage of USB would be that it is available on most machines, including > > laptops, while printer ports are becoming less available. > > > > I understand that it is not what you had in mind. > > > > 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 Till > > Harbaum > > Sent: Monday, April 23, 2007 4:17 AM > > To: Mario.; EMC developers > > Subject: Re: [Emc-developers] DIY USB interface > > > > > > Hi, > > > > what do you mean by "enumerate a few times"? USB enumeration > > takes place only once. > > > > I don't think we need to discuss the basics of USB as i have built several > > USB devices and have also written kernel drivers and libusb based user > space > > drivers for linux, windows and macos. So this all isn't a problem. > > > > The problem is that EMC just doesn't seem to be built to drive something > > like > > this. If i understand you correctly, EMC is tightly coupled to the real > time > > kernel > > which basically means that EMC isn't very modular. I was hoping that > there's > > some tiny real-time hardware layer under EMC and that i could just replace > > this. > > > > EMC seems to be designed tightly around its main control functionality. > The > > PC incl. EMC and the motor controller forms one big control loop. And now > > you > > and the others are suggesting to integrate the USB into this loop and keep > > the > > real time setup the way it currently is. > > > > IMHO this doesn't make sense at all. If you want to keep the real time > > kernel you > > can also stick to the printer port solutions. There's no real use for USB > > here, > > it will just add another layer of complexity and will cause additional > > trouble. I was > > hoping for a solution where i can move the entire main processing loop > into > > the usb device ... but i think you already understood that. > > > > Are there other linux cnc driver programs? Perhaps more simple ones? I > > really > > don't think that USB would be an advantage for the current EMC design you > > describe. Using USB would in fact make things worse. > > > > Regards, > > Till > > > > ----- original Nachricht -------- > > > > Betreff: Re: [Emc-developers] DIY USB interface > > Gesendet: Mo, 23. Apr 2007 > > Von: Mario.<[EMAIL PROTECTED]> > > > > > I dont't think it is entirely impossible and that hard. > > > You just need to enumerate a few times with the USB device and write > > > an interlayer software that will be the hardware part for the EMC. > > > Commands sent to the USB device have to be true commands, not just > > > single steps, and the feedback to the EMC needs some tuning too. > > > Depending on how much you aggregate the microfunctions into the sent > > > commands and how responsible your USB communication will be - the same > > > will be the success rate - the USB needs to respond quickly, so that > > > the software driver on PC will be able to correct its behavior. > > > > > > Since there are external controller boards and demuliplexers available > > > for use with EMC, it should too be possible to do with USB device with > > > some minor limitations - the USB is for toy devices, so I expect your > > > machine will be of the class, not a 5kW, 5 ton mill. > > > > > > I forgot the name of the few external controller boards that are > > > supported on EMC, but if you look at their drivers, you might get a > > > hint how to do that. > > > Learn more about the timers that are used in EMC2 and think about how > > > much time do you need between communication steps, etc. Typically, if > > > you would be putting out analog values, like the output of PID loop to > > > motor current control and have input of precisely measured motion > > > feedback, etc, you would only need the outer loop control, for say, > > > 100-200Hz interrupt rate. > > > > > > All you need is to know how to make an USB microcontroller program > > > with proper stack management and enumeration without an error. Also > > > you have to design it very responsible, quick to execute. PIC 18F or > > > the new PIC 24-bit code class with USB might be suitable for this due > > > to strict timing and exact time execution. > > > On the PC side you have to make some corrections to the output driver > > > in the EMC2 - it has to be able to tell how many steps to make, the > > > same for input. > > > > > > Mario. > > > > > > On 4/23/07, Till Harbaum / Lists <[EMAIL PROTECTED]> wrote: > > > > Hi, > > > > > > > > Am Montag 23 April 2007 schrieb John Kasunich: > > > > > But there are still issues. When you hit stop, does it stop NOW, or > > > > > after it works its way thru the queued motion? If you are doing > > > > You have at least two choices here: a) send some special emergency > stop > > > > command that overrides the buffers or b) Have the interface handle > these > > > > directly and just report to the PC that this happened. > > > > > > > > > While that is possible, what you would end up with would not be EMC. > > > It > > > > > would be a CNC controller based on a totally different architecture. > > > > Sounds like too much work. > > > > > > > > Till > > > > > > > > > > > ------------------------------------------------------------------------- > > > > This SF.net email is sponsored by DB2 Express > > > > Download DB2 Express C - the FREE version of DB2 express and take > > > > control of your XML. No limits. Just data. Click to get it now. > > > > http://sourceforge.net/powerbar/db2/ > > > > _______________________________________________ > > > > Emc-developers mailing list > > > > Emc-developers@lists.sourceforge.net > > > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > > > > > > > > ------------------------------------------------------------------------- > > > This SF.net email is sponsored by DB2 Express > > > Download DB2 Express C - the FREE version of DB2 express and take > > > control of your XML. No limits. Just data. Click to get it now. > > > http://sourceforge.net/powerbar/db2/ > > > _______________________________________________ > > > Emc-developers mailing list > > > Emc-developers@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > > > > --- original Nachricht Ende ---- > > > > > > ------------------------------------------------------------------------- > > This SF.net email is sponsored by DB2 Express > > Download DB2 Express C - the FREE version of DB2 express and take > > control of your XML. No limits. Just data. Click to get it now. > > http://sourceforge.net/powerbar/db2/ > > _______________________________________________ > > Emc-developers mailing list > > Emc-developers@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > ------------------------------------------------------------------------- > > This SF.net email is sponsored by DB2 Express > > Download DB2 Express C - the FREE version of DB2 express and take > > control of your XML. No limits. Just data. Click to get it now. > > http://sourceforge.net/powerbar/db2/ > > _______________________________________________ > > Emc-developers mailing list > > Emc-developers@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by DB2 Express > Download DB2 Express C - the FREE version of DB2 express and take > control of your XML. No limits. Just data. 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