[Noisebridge-discuss] getting that goddamned mill to work

[Dr. Jesus]

On Fri, Oct 2, 2009 at 10:13 AM, Andy Isaacson <adi at hexapodia.org> wrote:
> 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.

http://lwn.net/Articles/316622/

A quick check shows it's not in linux-next or any of the usual trees,
so you'll probably have to play build engineer for a while to get it
to work.

I've observed that some ACPI AML bytecode doesn't like it when you do
the trick the SMI detector does, so you might want to boot with
acpi=off or whatever it is.  You also might want to use PS/2 keyboards
instead of USB since I know of at least one system which gets into a
weird state where I can't type after running the detector for a while.