Re: [CAD_CAM_EDM_DRO] Mach3 & laptops

Danny Miller wrote:

> I was looking to set up Mach3 & a Taig with a laptop, and saw on
> Artsoft's website that "Laptops are not supported because the power
> saving features of the chipsets disrupt the pulse stream".
>
> What's the real story here? ALL laptops?? I'm kinda having a hard time
> believing this. Parallel ports are usually designed to... well, /work/
> at transferring data as designed. It's kind hard to even see this
> statement as credible, I mean the explanation borders on the absurd,
> power management and the parallel port datastream are two different
> things. Will this actually not work?
>
>

Well, we know ALL about this with relation to EMC. It is used with a
real time operating system, so we can measure the performance of the
computer hardware. We have seen not only laptops, but a number of
desktop systems that either have correctable or non-correctable problems
with real time delivery of CPU cycles. On the laptops, it is often due
to ACPI features of the main board, that interrupt the CPU for battery
and thermal management tasks. Some laptops have such poor cooling that
moving an entire window on the screen or some similar bit block transfer
task will overheat the graphics processor and cause it to slow down the
clock. This can also happen with certain CPUs, they will go to 1/10th
speed or even turn off the clock for fractions of a second when
overheated. A printer couldn't care if the data comes in spurts and
pauses, but a motor that is commanded by individual step pulses from the
parallel port sure would.

On some laptops, you can successfully turn all that ACPI stuff off, and
get around any video interference. On most, it becomes a real problem.
I have had to use plug-in video cards on several DESKTOP machines with
on-board video to get around real-time interference, but I had slots
there so it could be done.

> And what's a "non-integrated video card", one that's not on the mb like
> a laptop? Why would that matter?
>
>

Many on-board video chips use the system's main memory as graphics
memory. This takes a 10% or so speed hit all the time, but when doing
something graphically intensive, such as the above mentioned Bit-BLT
type operation, it can put the CPU on hold 50% of the time, slowing any
important programs to a crawl - like step generation. On a desktop with
slots, you can always plug in a card which has internal memory, but on a
laptop, you may be able to make video driver selections to alleviate the
problem, and you might not.

> My laptop does have a parallel port built into it. I could also get a
> USB-to-parallel port cable. That would add the complexity of the
> internal bridge and all but it would use a different data path than the
> internal serial port.
>

USB to parallel adaptors block and buffer the commands, spewing them out
in bursts, rather than the precise timing required. This will cause
motors to growl and stall. They also do not look like old-style
parallel ports at the device register level, so Machx and EMC will not
know how to talk to them.

Jon