Re: [Emc-users] Is it possible to disable video to fix latency issues

[Jon E. <el...@pi...>]

Patrick Rogers wrote:
> Hi,
> 
> I've installed EMC 2.2.1 onto an old PC from the BDI CD.  The system  
> works fairly well even though it is low on RAM and slightly under  
> powered.  When I run the RTAI Latency test however I get overruns,  
> and EMC itself refuses to run because of real time errors.
> 
> After reading some of the documentation I suspect the onboard video  
> in the machine.  Since I am connecting to the machine over ethernet  
> and using X11 to control EMC I am running the machine headless and  
> don't really need the onboard video.  (I have configured the machine  
> so it does not run the X server on startup and reduced the memory  
> available to the onboard video card as much as possible).
> 
> I don't have any other PCs around the house to cannibalize a video  
> card from and I was wondering if it would be possible to disable the  
> onboard video entirely without having to install another video card,  
> and if I did this would it prevent the realtime errors.  ie: is it  
> possible to tell the OS not to bother loading video drivers?
I think there are a bunch of video optimizations that can be 
turned on or off, such as hardware bit-blt (bit block 
transfers).  Maybe this depends on the specific X-windows driver 
for the video chip set.  I know a certain Linux system at work 
that had video hiccups and we were able to change some of the
harware acceleration and it fixed the problem.

Umm, if you are NOT actually manipulating the screen, then the 
hardware acceleration on the video chip set is NOT very likely 
to be causing the RT latency.  EMC REFUSES to run, or just 
reports a long latency?  Usually, these glitches occur when you 
move the mouse or set focus on a different window, and it has to
repaint the window from the backing memory.  That can involve a 
several megabyte copy from either system memory or a 
non-displayed part of video memory to the displayed video 
memory.  On machines with all memory combined on the main bus,
which some of the cheaper on-board video systems do, this REALLY 
ties up the memory and the CPU can't get much access, as the 
video stuff is totally in hardware.

There probably is a way to run X support without a local video
device, only a guru would know how.

Jon