Marcin Jakubowski wrote:

> Thanks for the responses on EMC laptops. But surely there must be at 
> least one specific laptop that does work? Is there any success story 
> out there at ALL for a working laptop?

I don't recall hearing about any that work well.  You may be able to 
tweak the BIOS a lot and end up with something that could work.

The problem isn't so much the parallel ports and pcmcia cards, it's 
interrupt latency.  Laptop computers usually have lots of power-saving 
features, and many of them can't be disabled in the BIOS (why would you 
want to, normally?).  The power management systems uses SMI (System 
Management Interrupt or Interface) to enter SMM - System Management 
Mode, and that interrupt must not be disabled (it's what alerts the 
system when the CPU is overheating, for example).  So when you close the 
lid, or some timer expires (usually every 64 seconds or so), an SMI 
interrupt occurs, which can cause latencies in the hundreds of 
milliseconds.  If that happened while you were generating a step pulse 
stream on the parallel port, your steppers would stall.

That's the real problem with laptops and realtime programs such as EMC2.
- Steve


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