#PLOT SPOOLER SOFTWARE
4 messages in this thread
Could anyone tell me what these programs do that can't be done with the DOS
print command? Is it the XON/XOFF handshaking? Better timeslice usage?
Something else?
Bradley:
You've covered most of it. First, they have to handle the Xon/Xoff. Next,
they've got to handle the time slicing, and provide for some fine tuing in
that area. If you want the spooler to work with AutoCAD's AutoSpool feature
they have to be able to watch for when DOS closes a file and then check to
see if it's an AutoCAD plot file in the spooler directory.
In order for the spooler to work efficiently it needs to have an internal
buffer so it always has data ready to pump out through the port once it gets
an Xon and once it's time slice comes along. And it works best when it's
interrupt driven which means it's got to work properly with the serial
port's UART chip.
It needs to be adjustable for the baud rate and communications protocols
that the plotter and/or CAD program expect to use.
So basically, the DOS print command is poorly suited for this task because:
1. it requires a different cable than AutoCAD's standard because PRINT
can't do Xon/Xoff.
2. PRINT doesn't let you adjust the time slice
3. PRINT isn't interrupt driven
4. PRINT can't queue automatically
There are other things a good spooler does as well, like queue management
and plot logs and things like that.
David
A few things, Dave.
Release 11's AUTOSPOOL feature can now invoke a spooler and pass it the
file name of the plot file that was just created. Waiting for AutoCAD to
drop a file into the spooler directory is no longer necessary.
IBM DOS 4 did support XON/XOFF (with the MODE command). DOS 5 does not.
The PRINT command's time slice is adjustable with the /s and /m switches.
PRINT can't handle 8-bit binary data because DOS traps ^Z, ^C, ^I, etc. and
PRINT seems to insist on sending a final formfeed (^L), so it will work for
most HP plotters, but will probably fail with Calcomps and Epson printer
plotters.
David:
Yes. I'm aware of AutoSpool's ability to call the spooler. But we've elected
to continue to watch for the plot file to be closed as well. Since not all
DOS versions support Xon/Xoff, I continue to treat PRINT as if it doesn't
(you never know which version someone is using until you ask). PRINT is
still not interrupt driven so it tends to slow things down even though its
time slice is adjustable.
David