[Noisebridge-discuss] getting that goddamned mill to work

[Andy Isaacson]

On Thu, Oct 01, 2009 at 11:56:29PM -0700, Jesse Welz wrote:
> 2009/10/1 dpc <weasel at meer.net>: 
> >Michael Wright <mike at smallip.com> writes:
> >
> >> After running the Jitter-Test program on the computer I have the  
> >> sinking suspicion that the machine we're trying to use isn't good  
> >> enough to send step and direction commands. 
> >
> >hmmm.... i never got around to schleping down the machine for the
> >reversing stuff but just noticed it has a prallel port. how good is
> >good enough?


The problem is that some low-end computers from about 1998 to 2003 (and
some up to the current day) use SMI mode (System Management Interrupt)
to do stuff on the CPU without letting the OS know about it.  This means
that at any moment your code may stop executing for up to a few hundred
microseconds -- plenty long enough to totally hose a PWM or stepper
motor pulse sequence.

The motherboard I last saw being used for the mill was a Via Eden CPU,
which is known to potentially have such issues.

Most "real" AMD or Intel CPUs' motherboards don't have these issues,
although it's not guaranteed (it depends on the BIOS and system vendor,
and laptops are also known for having such problems), so check for a
better mobo -- I know I saw a few in the E-Waste pile.

-andy