Re: [rtl] Newbie Stuff

[Andris Pavenis <pavenis@lanet.lv>]

On Wed, 13 May 1998, Theo ten Brummelaar wrote:

> Hi everyone,
> 
> Just started looking into RT systems for our new interferometric 
> telescope array on Mount Wilson, the CHARA Array. This consists of 
> five one meter telescopes in a Y shaped array, connected optically 
> (like an optical VLA). There are many RT systems involved. Besides 
> the telescopes themselves there will be delay line carts, fringe 
> tracking systems, tip/tilt systems and so on. All of these need to be 
> synced together.
> 
> I looked at commercial systems (VxWorks etc) but as we are a 
> University project the budget is tight, besides the whole Linux thing 
> appeals to me. We've been using Linux for some years now and I have 
> been playing with RT-Linux under the 2.0.33 kernel.  After only a 
> short time, I'm very impressed with the simplicity and ease of use.
> 
> My problem is, we will have many independent CPUs running various RT 
> processes, and they all need to be synced together somehow. Using the 
> simple scheduler that comes with RT-Linux is no good as it does not 
> use an external clock signal. My plan right now is to use some 
> simple electronics and the printer ports on the the machines to get 
> an external interrupt into all the machines, based of course on the 
> same clock signal. Rather than write my own scheduler is it stupid to 
> think I can modify the standard one to use an external interrupt 
> instead of the internal clock? Is there a more obvious way of doing 
> this?

I think there is no need to modify sheduler. You can simply use 
LPT interrupt from RT-Linux. 

It should work if You'll use ACK line in LPT, enable paralel 
port interrupts and use request_RTirq() in init_module and free_RTirq()
from cleanup_module. However I think some additional syncronization signals 
would be nice (full seconds, maybe something more) at least for startup. 
Fortunatelly we have additional input lines in LPT that can be used in 
that way.

> If people are interested I'd be happy to let them know how the 
> project developes, we've only just started out on the mountain and it 
> will be some years in the making. Our web site is 
> 
> http://www.chara.gsu.edu
> 

Andris Pavenis
pavenis@lanet.lv

Institute of Astronomy
University of Latvia
--- [rtl] ---
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