Till, Welcome to the list and to the EMC project.
Unfortunately, your idea would not work. EMC is a closed loop system. Every period, it reads the current position and computes commands based on the desired and current positions. It is not possible for it to buffer 8K bytes of commands ahead of time. However, I'm sure your usb skills would be valuable even though they do not mitigate the need for a real time kernel. Please stay on the list and contribute. 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 / Lists Sent: Sunday, April 22, 2007 4:10 PM To: emc-developers@lists.sourceforge.net Subject: [Emc-developers] DIY USB interface Hi, please excuse me for just starting a topic while being new on the list. I have recently got some use for a cnc milling machine to make some toys for my new-born daughter (always a good reason :-) I have thus taken a look at existing solutions and obviously found the emc project which perfectly fits that fact that i run linux on all my machines. But there's something that's "uncomformatable": emc requires a real time kernel and doesn't just run on my standard desktops. I do understand that this is due to the fact that generating proper motor timing requires the response times only a real time kernel can give, But for me a different solution exists: As you can see from some of my projects (http://www.harbaum.org/till/lcd2usb http://www.harbaum.org/till/i2c_tiny_usb http://www.harbaum.org/till/xu1541) you can see that i am quite successful in converting existing printer port solutions into usb ones. The projects above all have formerly used the printer ports just like most of the home cnc machines seem to do. What i'd now like to do is: Build a simple yet powerful USB to something converter that removes the need to use the printer port and more important avoid the need for a real time kernel. What i have in mind is a very simple device: Let's for simplicity reasons assume that we can run the machines in question at a constant signal rate. This means that the clock signals like e.g. required for the sc800 are updated at a maximum fixed rate. Lets assume this max rate is e.g. 50khz and we want to drive four motors with a direction and clock signal each resulting in 8 bits to be sent at once. We thus have to generate and forward 50kbytes per second. This is roughly 500kbit/s incl. control bits which are to be fed into the controller pcb at a constant rate. I can easily build a simple use device that inputs data via high speed usb (480 MBit/s), buffers it and forwards it byte per byte into the controller. If the interface has e.g. 8 kbytes buffer the PC has thus only to make sure it refills the interfaces buffer at least every 125ms. More buffer means even lower timing requirements. From the PCs point of view it would just try to write the data via usb as fast as possible. Once the device internal buffers are full the transfers are automaticall throttled and e.g. usb_write commands will block. As i said: I can build something like this, but i am not sure if emc can be converted to support this without requiring a real time kernel. Is this possible and are you interested? I would of course still need "example hardware" myself. I am thinking about e.g. a modified proxxon mf70 with the sc800 controller board. What do you think? 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
