trinity-users@lists.pearsoncomputing.net

Message: previous - next
Month: July 2016

Re: [trinity-users] Re: Re: Why does Trinity depend on Samba?

From: Gene Heskett <gheskett@...>
Date: Sat, 2 Jul 2016 23:17:50 -0400
On Saturday 02 July 2016 15:56:01 deloptes wrote:

> Gene Heskett wrote:
> > This is essentially 32 bit wheezy, with a special, pinned, rtai
> > patched kernel on the 3 machines actually moving metal cutting
> > hardware.  Same install on all 4 machines but because I've 8Gb of
> > ram in this box, and the rtai patches destroy PAE, and in this case
> > also put me 500 megs to a gigabyte into swap in 24 hours uptime, the
> > kernel was unpinned and I went hunting for one that could see the
> > 8Gb and use it, and could also run the simulated LCNC I use to write
> > gcode from a comfy chair. Found it in  3.16.7-ckt25-2~bpo70+1 and
> > pinned it again.
>
> I didn't know 32bit pc can use 8GB RAM. I thought it was limitted to 4
> because of the 32bit architecture.
>
Stick a fully functional PAE in the build config, and I believe it can 
use 64Gb.

But PAE takes time to do the translations, and rtai kills PAE because it 
needs every cycle it can get to run LinuxCNC if doing software step 
generation for stepper motors.  Put a 20% time wibble in the step 
generation when the step rate s/b 40 khz and the motor loses at least 
50% of its torque at the higher speeds, % of loss going up with the step 
rate, getting worse as the step rate goes up.  With modern drivers that 
do microstepping*, the step rate coming out of the driver card can hit 
300+ kilohertz.  But then you are up against the speed limit of the 
opto-isolators in that micro-stepping drivers input. So those of us who 
play with steppers, usually have the divisor set so that top rpms is at 
about 200 kilohertz.  Pure software generation is generally all tapped 
out at 30-35 kilohertz.

Your trivia factoid for the day. :)

*microstepping, where the driver can control the motors coil currents to 
do a successive approximation of 2 sine waves, 90 degrees out of phase. 
The motor then is balanced between steps, making a 1600 step motor out 
of the basic 200 step per revolution set of windings if the divisor is 
8.

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>