On Saturday 24 December 2016 15:59:31 Chris Albertson wrote: > Read the little write up at the Mesa site about cable length. They > claim ribbon cable is the worst and to only use it for very short > runs, 2 or 3 feet at most. They suggest using "real" parallel > cables made with twisted pairs and shielding for longer runs. Using > one of their fancy IEEE cables you can go up to 25 or 30 feet, half > that with a normal round cable and half that again with ribbon cable. > That would be about 6 feet, I'd assume src terminated. Mesa's cables, with plugs attached, I'd have to figure out how to get the plug past the 3/4" holes presently in the box. Even the ribbon that wide would need be to excavate and find some GreenLee punches I haven't used in 20 some years.
> For over 30 feet use some kind of differential signaling or fiber. > > There is nothing inherently bad about ribbon cable. It is more about > how it is driven. It works well as a 50 ohm transition line if you > terminate it at each end. The old SCSI disk drives did that. But not at 50 0hms! That ribbon cable, assuming every other wire is ground, has an impedance in the high tolerance end of 120 ohms. Assuming well by passed supply rails, the 220 from the signal line up to the 5 volt rail, in parallel with the 330 to ground, simulates a 132 ohm parallel termination on each end. Under ideal conditions the cable length limit is said to be 39 meters! But that has one huge gotcha that the bean counters between engineering and the production floor, busy counting sheckles, substituted an Si diode for the schottky the engineers specified for the rail isolator, thereby dropping the nominally 5 volt bus, which should rest a logic 1 at 3 volts, to about 2.6 volts, eating 400 mv of the logic 1's 600mv noise margin. Back in the day, when every midmarket tv station had half a dozen Amiga's doing graphics work, and crashing due to scsi bus errors, I had to fix every damned scsi card we ever put in an Amiga. And one of the two we had in pc's. No exceptions in the Amiga's. And I found some mistakes that were real hooodooozies. Like the term resistor packs all installed end for end. Or all the 6.3 volt electrolytic's installed on the 5 volt rails soldered in bas ackwards. Surprisingly, those caps will last about a year that way, so by the time they start blowing their tops, any warranty of a $1500 68060 card was long expired. Theres an awful lot of such stuff I've had to fix in the 66+ years I've chased electrons for a living, and at 82, I am still doing it occasionally. But understandably getting rusty too. So I ask lots of questions now. :) > But > there is an upper limit on how fast you can push data down a parallel > cable. This is why all the really fast computer interfaces are now > serial > > Your problem might be because you are doing to much at once. Can you > get a one axis stepper motor to run slowly using GPIO and no FPGA > card? Does that work reliably through multiple upgrades and config > changes or is it fragile? Or even before that, can you install and > update Linux and compile kernels and instal new drivers and run a web > browsers and email and do upgrades and such reliably before using > RPi3 as a machine controller. At this time, I would have to say that its damned fragile. This msg sat behind the main window while I played a bit last night, and made it run with x remoted to this machine. And I am seeing a data error that is causing it to throw joint errors, including a joint that is yet open pins on the 7i90 output connectors. I am thinking that a study of the 7i90 pdf might have a clue, because the 7i90 is still jumpered as shipped, but the r-pi is feeding it only a 3.3 volt signal. (assumed, I have not pulled out the sampler and measured it, so I suppose thats next) In previous playing a month ago, I found if I could keep it moving the z axis at a typical rapid move rate, it did not throw the joint error while the z was moving. Only after it had stopped, did it error, always both joints. So IMO it almost has to be signal level caused data errors. The interconnect cable I made has all 8 of the available grounds on the pi's 40 pin header, connected thru to the 8 available grounds of the 7i90's 26 pin connector. And with the box cover carrying the pi and 7i90 on its inside face held open, I cannot see radiated noise from the z axis driver, or its switching psu, getting back into the pi by any means than a possible ground loop. Thats problem #1. The second problem is that I can't make x run on the pi. And without synaptic I can't see whats missing. It opens a black screen with what almost looks like a prompt at the upper left corner, but thats as far as it gets, and any recovery must be done from a login from one of the other machines here. But an xhost + in the terminal tab I am going to log in from, fails to allow me to run a package manager other than apt. Screen scrape: gene@coyote:~/.ssh$ xhost + access control disabled, clients can connect from any host gene@coyote:~/.ssh$ ssh -Y pi@raspi Warning: the ECDSA host key for 'raspi' differs from the key for the IP address '192.168.71.8' Offending key for IP in /home/gene/.ssh/known_hosts:19 Matching host key in /home/gene/.ssh/known_hosts:20 Are you sure you want to continue connecting (yes/no)? yes pi@raspi's password: The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. Last login: Sat Dec 24 19:49:11 2016 from coyote.coyote.den pi@raspberrypi:~ $ synaptic-pkexec ==== AUTHENTICATING FOR com.ubuntu.pkexec.synaptic === Authentication is required to run the Synaptic Package Manager Authenticating as: root Password: polkit-agent-helper-1: pam_authenticate failed: Authentication failure ==== AUTHENTICATION FAILED === Error executing command as another user: Not authorized This incident has been reported. pi@raspberrypi:~ $ synaptic-pkexec ==== AUTHENTICATING FOR com.ubuntu.pkexec.synaptic === Authentication is required to run the Synaptic Package Manager Authenticating as: root Password: polkit-agent-helper-1: error response to PolicyKit daemon: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: No session for cookie ==== AUTHENTICATION FAILED === Error executing command as another user: Not authorized This incident has been reported. ================================== I tried both the root pw and mine. WTHeck is this com.ubuntu.pkexec.synaptic BS? Of course its wrong, but how can this be fixed so I can run synaptic from a remote login? Or, how do I make this machine accept a display of 10: ?? Thank you all & Merry Christmas everybody Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/intel _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
