Forward 
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Here at Engineered Audio, we use a variety of test equipment. We have several O’scopes (Tek TDS340A & Tek 2232), spectrum analyzers (Tek 2794 & HP 3561A), a nice Vector Network Analyzer (HP8753D), a pen plotter (7475A), and various other counters, DMM’s, and power supplies (Tektronix PS5000 series). And the 1 thing they all have in common is a GPIB/HPIB interface. 
 
So, in the not-too-distant past, it was a cumbersome process to take measurements and “plot” the output from the test equipment. First we would send the output to the pen plotter, take that hard plot and scan it into the computer, and then email/archive/print the resulting scanned PDF file. 
 
In a word - Yuck. 
 
Over the past year, we have been playing with a National Instruments Enet-GPIB converter, and while this works great for controlling the various devices (from a Macintosh I might add), it was still cumbersome for printing. What finally made the whole process bearable was finding the Tektronix AD007 GPIB-Ethernet interface. 
 
The magic to the AD007 is that it can do simple print redirection and redirect the GPIB data to an LPD print server. Lucky for us, we have several Mac OS X servers that can (and do) act as print servers. 
 
I’ve asked Bill to write up a small article on how this all came together recently. 
 
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Extending OS X's print services to include better HPGL support 
and PCL support. 
 
By Bill Siever 
 
Motivation 
---------- 
 
The goal is to extend Mac OS X's print server (CUPS), so it can  
translate either a HPGL or a PCL file to a printable format  
(postscript or PDF). Specifically we have HPGL and PCL files  
being generated by test equipment and sent to the print server 
(via a GPIB to Lan bridge). The equipment generating HPGL files 
are slightly different from the formats that CUPS is configured  
to recognize, and consequently weren't being printed. In addition, 
we'd like to be able to adjust the output settings to make each  
look pretty.  
 
Disclaimer 
---------- 
 
We've tried to list all the critical steps, but we assume some  
background working with OS X and the console. (That mysterious 
"Console" application in Applications->Utilities. If you don't 
know how to deal with the blinking cursor, this may not be the  
guide for you). In addition, this is just a quick and dirty way  
to get our network setup to print files for our test equipment -  
it may not be the best choice for other setups. For example, 
if your printer can natively handle PCL and you're happy with 
the format of the PCL files you have, this may not be the best 
setup for you. 
 
Steps 
----- 
There are three basic steps to the process: 
1. Download and install programs to convert formats 
2. Update CUPS 
a. Create and Install filter scripts for conversion  
b. Update Mime Types & Converters  
3. Restart CUPS 
 
Step One - Installing utilities for conversion 
---------------------------------------------- 
In our case the default hpgl converter that comes pre-installed 
didn't allow us to format the output as we'd like, so we decided 
to use another program. In addition, there isn't a default converter 
for PCL formatted files (by default they are directly dumped to the 
printer - which works fine if your printer speaks PCL and you're  
happy with the format) 
 
For HPGL: 
Download hp2xx 
http://www.gnu.org/software/hp2xx/  
(Note that this isn't a direct link - you'll have to follow the links 
to a mirror, find the hp2xx directory, and download the latest source 
code) 
Extract it and install it on your print server. 
For me this required: 
cd Desktop 
tar -xzvf hp2xx-3.4.4.tar.gz 
cd hp2xx-3.4.4 
cp makes/gnu.mak sources # Get the correct makefile 
# In my case I had to edit the make file and disable TIFF and JPG support 
# because I didn't have the appropriate libraries installed. 
# I just commented our the four lines in sources/Makefile following 
# "TIFF support", and the next four lines with jpg. 
 
# Now install it 
cd sources 
sudo make install 
 
# Note that hp2xx is now insalled in /usr/local/bin 
 
 
For PCL: 
Download GhostPCL 
http://www.artifex.com/downloads/ 
(I used a mirror: 
http://www.ctan.org/get/nonfree/support/ghostscript/AFPL/GhostPCL/ghostpcl_1.41p1.tar.bz2 ) 
 
Extract and install if on your ptint server. 
For me this required: 
cd Desktop 
tar -xjvf ghostpcl_1.41p1.tar.bz2  
cd ghostpcl_1.41p1 
make 
sudo make install 
# Note that it is also installed /usr/local/bin The executable is named pcl6. 
 
Step Two - Updating Cups 
------------------------ 
The defaults CUPS configruation provides several filters to convert from one 
file type to another. It also contains two kinds of "rule files". There are  
"types" files that look at elements in a file to try to deduce the type of 
file (like whether it's postscript, PCL, HPGL, etc.) and there are "convs"  
files that provide rules for converting from one type to another. 
More info on the process and how conversions are done is available in  
the CUPS documentation: 
http://us1.samba.org/samba/docs/man/Samba-HOWTO-Collection/CUPS-printing.html#id415801 
 
In this step, we'll add in two new filters - these will just be scripts 
that use the two programs we've just installed. The scripts allow use to  
specify command line arguments to perform some formatting. Then we will  
update the CUPS configuration files so that they will use our scripts for  
HPGL and PCL files. Some of the equipment we use generates HPGL files that 
don't match the default HPGL type rules, so we'll also update the rules 
to recognize our HPGL formatted files. 
 
Part 1 - Creating filter scripts 
 
The filters used by CUPS are just programs that need to follow a specific 
pattern. (See the man page for full details - "man 7 filter"). We aren't  
worried about header pages or job ids, etc. - we just want an intermediate 
filter rather than one that rasterizes to the final printer-destined output,  
which may need this extra info. in some environments (large offices)).  
You can copy the provided files to /usr/libexec/cups/filter/ ,  
then be sure to change permissions and ownership on them: 
sudo cp hpgl2ps.sh pcl2ps.sh /usr/libexec/cups/filter/ 
sudo chmod 755 /usr/libexec/cups/filter/hpgl2ps.sh /usr/libexec/cups/filter/pcl2ps.sh 
 
Part 2 - Update CUPS configuration 
Become root. 
Edit: /etc/cups/mime.types 
You may need to modify the strings in the file to correspond to 
those output by your devices. In our case, the HPGL files have DF;  
in the first few characters, but it is'nt the first character.  
We modified the HPGL recognizer by changing: 
 
string(0,DF;&#41 
To: 
contains(0,15,DF;&#41 
 
Add in a new line to recognize and convert the PCL files: 
application/pcl pcl string(0,<1B>*rA) 
(Our PCL generating equipment starts the file with ESC*rA) 
 
Edit: /etc/cups/mime.convs 
Replace hpgltops with hpgl2ps.sh 
Add a line for pcl: 
application/pcl application/postscript 33 pcl2ps.sh 
 
 
Step Three - Restart CUPS 
------------------------- 
Restart the print server. From the console on the server you should  
be able to accomplish this via: 
 
killall -HUP cupsd;