Radeon question

Gene Heskett gene.heskett at verizon.net
Fri Oct 9 08:09:52 PDT 2009


I am trying to setup an 8.04 system to run emc, the machine control program, 
and I'm observing something odd.

The video card is a 9200SE, driver is radeon.  Cpu is 1GHZ athlon, 384 megs 
of dram.

glxgears shows about 560 fps.

This program would normally issue screen updates at 10/second, but I have 
changed that all the way from 5 to 30 with essentially no difference to be 

The problem is that the backtrace being drawn as the tool moves about the 
work, does not follow a discrete position per screen update, which when 
following a curved 'cut', or encountering an angle that is 90 or less 
degrees, acute IOW, the tool position doesn't follow a series of discrete 
points that would represent the tools position at that particular instant, 
but instead draws a very nicely smoothed arc that can for instance at the 
center of an "M", miss the bottom of the V by 1/4".

This program has the ability to make sure the tool is stopped at the exact 
point, and if that option is set, then the drawing is good, but setting it 
for an error of .0001" without stopping the tool completely, and the errors 
in the display are back.  The complete stop, according to my theory, gives 
the display time to catch up as its stopped for at least a millisecond under 
those constraints.

Also, if I hit the emergency stop, the machines motion is instantly frozen, 
stopping any motions as fast as the motors can be brought to a stop, but 
typically before the tool has moved another .005".  But while that seems to 
work, about 1 second later, or perhaps a little quicker, the image of the 
tool will snap as much as 3/4" inch to its true position, depending on how 
fast it was moving when the e-stop was hit.

Can the radeon driver, as shipped with *buntu 8.04 LTS, actually get that far 
behind and then do a catchup?

 And can it blend short segmented straight lines into smooth arcs?

If any of this is true, then I may have to revert to the vesa driver, which I 
have also found doesn't lock out the interrupts for nearly as long, allowing 
the machine itself which is stepper driven, to be run at least twice as fast, 
this on a kubuntu-6.06 box also running this same program.

Cheers, Gene
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