AIX Printer Support: Colon Files

Jeff Courington

One of the first questions your manager will ask when he/she finally decides to jump on the open system bandwagon is "Can we use all of our current terminals and printers on the new platform?" I was asked this question before my company purchased 10 IBM RS/6000's as badly needed replacements to our aging MAI/Basic 4 systems. MAI were very helpful in answering the hardware side of the question: most of the current terminals and printers would work with some minor changes and converter boxes, but some of the older equipment would have to be replaced. I soon discovered, however, this was only a small part of the solution. Since these were non-supported printers, many functions -- such as form length, cpi, and lpi -- were not available. So the question became "How do you regain the functionality of non-supported printers?" AIX's answer is called the colon files.

A colon file is simply a text file that can be used to control characteristics of the printer. A stack-based language is used to pass commands, and the colon file is compiled by the chvirprt command. The resulting "digested" file is used by the formatter programs. The formatter is actually a C program that acts as a filter to perform the tasks defined by the colon file. The formatter to be used is specified on the mf line of the colon file. The pio commands load the colon file to find which formatter is to be used and then load the appropriate formatter. If you have a lot of time to waste you can actually write a formatter, but the ten that IBM has supplied should work for most of your needs. Once you've seen these files, the reason for the name becomes obvious.

I was first introduced to colon files through two internal IBM documents -- "Printing for Fun and Profit Under AIX V3" and "Printer Formatters, Colon Files and Virtual Printers." The internal document number for the first is GG24-3570. The second document does not have an internal document number but the majority of the information it contains is in info explorer under "Printer Colon File Conventions" and "Printer Colon File Escape Sequences."

The printer I needed to configure was an MAI 4201. This is almost a Printronix P6000 series printer. MAI made some hardware modifications to allow their system to communicate, but a converter was supplied to negate those changes.

Standard Configuration

To start working on a non-supported printer, first configure the printer as another serial printer, that is, a generic RS-232-type printer, then add a virtual printer of type ASCII. This gives you a clean colon file to start.

Form Length

Most newer printers allow form length to be loaded by a simple escape sequence, e.g., ESC C n, where n is the number of lines per page, but this printer used a method called vertical form units (VFU). A short explanation from the hardware reference manual summarizes VFU as a device that permits executing forms of up to 132 lines in length and allows slewing within a form. To accomplish this task with hex codes requires the following:

1E 10 1D ... (number of
lines - 1) ... 1D 1F.

The 1E tells the printer that you are starting to load a VFU; the 10 signals the printer that this is the top of the form. The 1D values are place holders for the rest of the lines on the form, and there are number of lines per page - 1 of these. The top of form accounts for the need to use -1. The 1F tells the printer that you have finished.

To accomplish the same thing with a colon file requires a different procedure. The files can be found on AIX 3.1.x in the directory /usr/lpd/pio. Changes will be kept in the directory /usr/lpd/pio/custom. The file names are <virtual printer>:<physical printer>. Predefined colon files are in the directory /usr/lpd/pio/predefs. Printout headers are in the directory /usr/lpd/pio/burst. After the colon file is compiled by the chvirprt command, the "digested" file is placed in the /usr/lpd/pio/ddi directory. This is the file that is actually used by the formatter programs. If the colon file is not re-compiled the changes will not take effect. On version 3.2 these directories were changed to /var/spool/lpd/pio.

A clean colon file would resemble Listing 1. The relevant entries are as follows:

:076:_j::1
:079:_l::66
:144:ci::
:183:eC::

_j is a boolean used to decide if form length needs to be loaded. _l is the number of lines per page. ci decides whether or not to load form length by looking at _j. eC loads form length.

The modifications look like this:

:144:ci::%?%G_j%{1}%=%t%I[eC,al]%?%Gwp%t%I[c2,
eB,eD,e%]%;%;
:183:eC::%?%G_l%t%G_l%{1}%

-%Pa\36\20%wa\34%;\37%e%o%G_l%r%t%\33C%o%G_l%r%c%;

The first clause

:144:ci::%?%G_j%{1}%=%t%I[eC,al]%?%Gwp%t%I[c2,
eB,eD,e%]%;%;

says, in English,

If the value of _j is equal to 1
then run the eC clause and the al clause
If the value of wp is not equal to 0
then run the c2, eB, eD, and e% clauses.

The last if clause is the standard ASCII printer clause and can be removed.

The important clause is the eC clause. You should be aware that this clause does not even appear in the standard colon file. I found this number by looking at the IBM ProPrinter colon file and used it as a rule of thumb.

The second clause

:183:eC::%?%G_l%t%G_l%{1}%-%Pa\36\20%wa\34%;
\37%e%o%G_l%r%t%\33C%o%G_l%r%c%;

says, in English,

if the value of _l is not equal to 0
then subtract 1 from _l and put it in the
a register
send octal 36 and octal 20
while a does not equal 0
send octal 34 and send octal 37
else use original options from database
push _l on the stack
reset the value before %o was used
then send octal 33 the character C
use original options from database push _l
reset the value before %o was used
pop integer off of stack and use low order byte.

The else phrase is a standard loading of form length for an IBM ProPrinter. The values are first set to the originals, in case you changed something, then reset. The code looks to see if a form length is set, then sends octal 33 to the printer along with the ASCII value of C. It reloads the original values, pushes the value of _l, and resets values, then pops values of _l. Listing 2 shows a more technical breakdown of the information. Figure 1 displays the command set.

You can make these changes through smit -- you change the virtual printer, which causes an automatic recompile. I usually bypass this and use the vi editor, but I then must manually recompile using the following command:

-> chvirprt -d<physical
printer> -q<virtual printer>

If doing it yourself seems too complicated, IBM says they may help (see sidebar).

Don't be nervous about changing the colon files -- the original can always be recovered by deleting the virtual printer and redefining. This example is only the beginning of what can be done through with colon files. If you want an explanation of the other values, use smit to change/show virtual printer. The result will be a list that consists of a two-character description, its purpose, and possible values.

About the Author

Jeff Courington graduated from Virginia Polytechincal Institute and State University with a BS in Computer Science. Over the past eight years, he has worked on various forms of UNIX, including AIX, SCO, SVR3 variants from Silicon Valley Software and Versyss Corporation. He presently runs a network of 10 IBM RS/6000's and various SCO machines connected by X.25 over the wide area and Ethernet on the local area, also running TCP/IP over X.25.