Re: Linux vs. DOS

> Andrew Werby wrote:
>
> [Oh. I really don't know anything about Linux, but it seems intimidating.
> All the problems with "kernels", whatever they are, seem like they would
> take over my life. I read some previous discussion here on the fine points
> of running Linux , and I didn't understand thing one. Is there no
> alternative? Does NT run in real time? Has anybody built a graphical user
> interface for Linux that makes it more user-friendly? Is there a Linux for
> Dummies?]

1. If you have the brains to contemplate retrofitting a servo controlled
cnc mill, do machine work as a hobby, and subscribe to this newsgroup, then
you have enough brains to deal with Linux. It looks really bad going into
it, but once you get over the initial hump in the learning curve it's not
bad at all. In fact Linux is becoming more and more popular all the time,
so unless you're already retired, there's more than a small chance you're
going to have some contact with it in the future if you work with or around
computers for a living. There's no time like the present to get up to
speed. By the way, DOS has a kernel too. It is found in two hidden files in
the root directory of the boot disk called MSDOS.SYS and IO.SYS. There
doesn't seem to be a /dos/src directory though... One difference between
the two systems is that support for accessory hardware devices is handled
in DOS by loading device drivers in the CONFIG.SYS file with a line
such as DEVICE=C:\MYDEVICE.SYS. In Linux this support is provided by
including the code in the kernel which means that the kernel is re-compiled
to add support for new hardware. In truth, Linux also has loadable modules
as well, but they are optional. Also, in Linux, there are directories full
of files that perform the function of DOS's AUTOEXEC.BAT and CONFIG.SYS.

2. Linux is a much more reliable OS (doesn't lock up, get weird, or give
you the "blue screen of death") than Win95/98 or NT and the only
alternatives for a real time control application are systems like QNX and
LynxOS which are specifically meant for real time control. They are
expensive and there is a lot of debate (and I mean among guys with PhD
behind their names) on the RTLinux mailing list about whether there is any
real advantage to these systems over RTL.

3. All the inexpensive control programs that folks talk about on RCM and
this list such as DanCAM, MaxNC, Stepster, etc. are only for use with stepper
motor systems. This is to say that they output axis motion commands in the
form of step and direction signals. You would be much better off to keep
your existing servo motors, amps, and encoders due to their higher
performance. This leaves alternatives like Lighthouse Software (big $),
Delta-Tau (MEGA $), Bestsoft (no one can seem to get tech support), or a
commercial control such as Centroid or Fanuc, or ... This is the gap that
the EMC fills.

4. See my previous, very long post, for comments on NT and real time.

5. Caldera's latest version of OpenLinux has a graphical install and comes
with a nice window manager called KDE (which I use on my Red Hat Linux
system as well). You can download KDE from http://www.kde.org .The only
problem is that the EMC doesn't run under the newer 2.2 version of the
kernel yet, so you'll need to stick with Red Hat 5.2 (which uses the 2.0.36
version of the kernel) for the moment. The installation isn't as bad as you
think, and you'll reduce your problems a lot if you pick hardware from the
compatibility list you can find at
http://www.redhat.com/corp/support/hardware/intel/52/rh52-hardware-intel.htm
l .

6. Yes, I think there is a Linux for Dummies book, but there is also a lot
of documentation that comes with the boxed version of Red Hat Linux. There
is a printed installation manual and many helpful files in /usr/doc once
you get it up and running. In fact the online documentation on networking
goes into some information on how Microsoft's networking scheme works, and
this helped me solve some Win 95 problems I had been having! There is also
the Linux Documentation Project at http://metalab.unc.edu/mdw/ .

> [Would that be better than leaving the old relays in place? Also, can you
> tell me why there's a strong smell of methyl mercaptans in the mill's
> control box? If I didn't know better, I'd swear it was leaking natural
> gas...]

You'll need most, if not all of the existing electrical gear in your
control to run thing like the spindle, coolant pumps, etc. The solid state
relays that Jon refers to are simply an interface between the TTL level
world of the computer and the coils of the power relays you are talking
about which are probably actuated by 24 or 110 volt signals. You really
need to understand how you present system works before you attempt to
change it. Are their any schematics or other documentation like a
maintenance manual that came with the machine, or which you could get?
These will be INVALUABLE to you when you go to rewire things! I'll venture
a guess that the smell is transformer varnish cooking.

> [If you'd rather, we could take this off-list, but it seemed we were still
> discussing things of general interest, so I'm replying in "public". The 8
> axis Servo-to go card sounds interesting at $888 - it certainly beats
> paying $1500 per axis. They mention running NT in conjunction with their
> card, and something about how it (and DOS) can be induced not to interrupt-
> do you know anything about this? They also talk about writing your own
> algorithms, though- so I'm not sure how hard this would be. ]

What they are talking about are real time extensions to NT written by Venturcom
and other third party developers. I don't believe they have as good a level of
performance as RTLinux, probably because the developers didn't have access to
all the source code for the NT. In addition these extensions cost a lot of
money for the developers kit, plus a per machine runtime license, in addition
to the cost of NT itself. As for writing your own algorithms, if you can do
that, well, let's just say you don't need any of my advice. I'm happy to see
this discussion stay on the list as I think there is a subset of subscribers
who is interested in this sort of thing. As I've said before, if you need any
help in getting the EMC up and running, don't hesitate to call or write.

Matt Shaver
(410) 521-3715
mshaver@...