SPACE 1/SPACE - Library 1 - Volume 1.iso/utilitys/104/yaps.doc

Text File | 1987-09-20 | 12.4 KB | 200 lines

                             "THE BEGINNING"

        So you purchased a 520ST computer. You did so because of its price (a-
huh), but also because is was advertised as being a "powerful" computer using
Motorola's FAST "68000 CPU".  So you rush home with your computer, monitor, and
disk drive and put it all together. Then you get a fancy word processor and new
printer, and, voila', you can now write letters to your Aunt May!

        Five weeks later (maybe sooner if you read ST Log) you begin to notice
that your FAST computer runs everything at "great-guns" until it comes time to
print out that letter to Aunt May. The computer then slows down to an "ants
pace" (pun intended) while it WAITS for your slow-as-molasses printer to punch
out that letter. Isn't there a faster and better way to print out that letter
without spending any more money? YES!!!! Why not use your speedy computer to
store your letter in a buffer, sending it to your printer character-by-charac-
ter at the printer's slow pace, and otherwise running other wonderful programs
that you tell it to.

        And that's what a "Yet Another Printer Spooler" (YAPS for short) does
for you. This little program wedges itself permanently in memory (or until you
turn off or reset your computer). It then patches itself into the operating
system (low level BIOS calls) and waits for someone to send a character to the
printer. When that happens, it checks to see if your printer is busy printing a
character. If the printer is not YAPS sends it a character to print. However,
if it is busy, YAPS will store that character in a buffer and return to your
program.  Then YAPS "wakes up" and checks to see if your printer is ready to
receive another character. If so, it sends one on and then returns control to
any program you happen to be running.


                               "THE SETUP"

        "Yet Another Printer Spooler" works with practically all printers that
connect to the Centronics Printer Port in the back of your ST computer. It will
even work with some printers that do not work with TOS (see below for Why?).
YAPS can be run at any time to set up its buffer and patch itself into the
operating system, but is probably MOST effective if run at the time you turn on
your computer.

        There are two (2) versions of YAPS included in the arc'd file,
YAPS_C.PRG and YAPS_T.PRG.  YAPS_C.PRG uses the Centronics Busy Signal
interrupt to know when to send characters to your printer. It therefore is the
most efficient of the two versions, and runs generally faster (especially if
graphic information is being sent to the printer, as with Publishing Partner).
YAPS_T.PRG runs off of timer C. This version is compatible with more printers
than YAPS_C.PRG, but may, in certain instances, run noticeably slower. Try
using YAPS_C.PRG first, switching to YAPS_T.PRG if you have problems with a
particular application or printer.

        Before you run YAPS you should decide how big a buffer you want
to be set up. The default size is a 32 k (kilobyte) buffer, but any size up to
the available size of your memory can be set up! You must then change the name
of the program you want to use to reflect the size of the buffer you want to
set up. For instance, if you run "Yet Another Printer Spooler" with the name
YAPS64.PRG a 64 k buffer will be set up to store printer characters. If you own
one of the new MEGA ST's and want to set up a 1500 k buffer (a whopping size),
then you would rename the program YAPS1500.PRG before running it. The smallest
size buffer that can be set up is 1 kilobyte in length (YAPS1.PRG). Remember,
however, that the program name must begin with YAPS and have an extension of
PRG for everything to work properly.

        The program can be run from the GEM desktop. However, you can also
start YAPS automatically. To do so, format a new diskette, and create a
folder called AUTO. Then copy all programs that you wish to run at the time
you turn on your ST computer into this folder, INCLUDING the YAPS file that
you just renamed. The next time you turn on your computer make sure that this
diskette is in DRIVE A, and "Yet Another Printer Spooler" will load in auto-
matically.


                       "SOME ADDITIONAL FEATURES"

     There are a few more features that YAPS has to make your life easier:

   (1) When YAPS is run, if you press either the "Alternate", "Shift", or
       "Control" keys,  the  installation of the  printer spooler will be
       aborted. A  somewhat rude message  will appear then,  telling  you
       of the abortion (I  mean aborted installation...).  You can  still
       load in YAPS at any time from the GEM desktop.  Remember to  first
       rename the program to reflect the  size of the printer buffer that
       you want to be set up.

   (2) If there is not enough memory  available to set up the buffer size
       specified in the program name,  installation will be aborted,  and
       a message printed on your screen indicating this.

   (3) If YAPS can not  interpret the  size of the buffer needed,  or can
       not find the program name, a 32 k (default) buffer will be set up.

   (4) There  is a  way to  CLEAR the  buffer before YAPS  has  completed
       spooling the  characters to your printer.  If you  run the program
       again after it has already been installed,  you will get a message
       indicating that the  printer spooler is running, and asking if you
       want to clear to buffer.  Press  "Y"  to do so, or "N" not to stop
       the printing.


                         "THE TECHNICAL ASPECTS"

        "Yet Another Printer Spooler" is written in assembly language using
Abacus's ASSEMPRO. It works by stealing the BIOS (trap #13) vector from the
operating system, and then checks for CONOUT and CONSTAT calls directed at
the printer.  All other BIOS calls are passed on to the operating system.

        As the program starts it first checks to see if another version of YAPS
has already been installed by looking for the 8 byte name "YAPS.PRG" near the
beginning of the trap #13 code. If the name is found, the program informs the
user that "Yet Another Printer Spooler" is already active. It then gives the
option to clear the printer buffer of its contents.

        In the next step YAPS looks for its name by doing a GEMDOS directory
search using the wildcard mask "YAPS*.PRG". If no match is found in the current
directory, YAPS will look for a match in an AUTO folder. I know of no other way
to get the program name other that doing a directory search, and still be able
to run YAPS in an AUTO folder. There is an inherent limitation; YAPS will find
the FIRST match to the wildcard mask, and NOT necessarily the actual program
name run. For instance, suppose a copy of YAPS is kept BOTH in the root direct-
ory (ie. - not in any folder) AND in an AUTO folder of a boot diskette. The
filename in the root directory will ALWAYS be found first. This filename ONLY
will be used to determine the size of the printer buffer to set up even if the
program is run from the AUTO folder when the computer is booted. So a good rule
of thumb when using YAPS is to try NOT to keep multiple copies of the program
around on the same diskette.

        After the buffer size is determined, YAPS then either ties in the
printer spooler portion of the program to the 200 hz. system timer (TIMER C of
the MFP chip) or sets up the Centronics Busy Signal Interrupt Routine
(depending on what version of YAPS you are running). YAPS_T.PRG uses the XBIOS
SETEXEC call to find the current TIMER C vector, then uses the same call to
chain the printer spooler routine with the current TIMER C handler.  I chose
to use TIMER C in order to be compatible with most other applications run.
Using TIMER A and resetting to a faster speed (lets say 700 hz.) may increase
to speed of spooling with those printers that have no more than 1 line of
buffer, but at the cost of being potentially incompatible with other
applications that may use this timer for there own purposes. For the vast
majority of printers the speed of printing should be no different with the
spooler as compared to the operating system calls.

        If you plan to print graphic material with your printer (as with many
drawing and publishing programs currently available), you will find that the
timer C version will not be able to feed the graphic information to your
printer as fast as it can handle it. Your printing can, in fact, run SLOWER in
these cases than if you did not have any printer spooler installed. For this
reason a second version of YAPS is supplied, YAPS_C.PRG. This version runs off
of the Centronics Busy Signal Interrupt (also of the MFP chip); that is it
sends characters to the printer at the exact time the printer is ready to
receive characters, not by polling the state of the printer when using TIMER C.
This version may potentially not be compatible with some applications, since
it steals rather than chains to the Centronics Busy Signal Interrupt Vector
(I have yet to find any application that it can not run with so far). This
version of YAPS may also not driver certain printers properly (such as the
Texas Instruments model 810), though it will probably work with more than 98%
of printers currently on the market.

        To finalize the setup, the SETEXEC call is again used to steal the
trap #13 (BIOS) vector. Finally the program is exited using the GEMDOS KEEP
call to retain the printer spooler with its buffer in memory.

        I originally wrote this printer spooler to work with Texas Instruments
(TI) 810, 880, and 850 printers (these are heavy duty printers frequently used
by the airlines and ticket agencies). These three printers do not work with
the current operating system print routines. If these printers are attached to
any ST computer, DUPLICATE characters will be appear on any document printed.
The fault lies with each manufacturers interpretation of the Centronics Para-
llel Interface Protocol. In order for the printer to grab or "latch" on to a
character to print, it has to know when the character is available. The compu-
ter signals the printer when ready by flashing a flag called the STROBE. The
STROBE signal must be pulsed a minimal amount of time before the printer will
recognize that there is a character to print and grab it. The Parallel Inter-
face Protocol specifies this MINIMAL time to be either 0.5 or 1 microsecond for
almost all printers. The protocol does NOT specify a MAXIMUM time, and that is
where that problem arises with some printers. Most printers (let's say 95%) not
only wait for this STROBE flag to be raised (or technically set LOW), but they
also wait for the STROBE flag to be dropped (or technically set HIGH) before
they process the character and look for another one. A few printers latch onto
and process the character sent to them as soon as the STROBE flag is raised.
After they finish processing the character, if the STROBE flag is still raised,
they latch onto the same character and print it! It then becomes critical that
the ST computer flash the STROBE as near to the minimal time specified in the
Parallel Interface Protocol as possible in order to work properly with these
"few" printers.

        The STROBE signal is controlled by the Yamaha YM-2149 Programmable
Sound Generator (PSG) chip. The normal BIOS call to send a character to the
printer pulses the STROBE for greater than 8 microseconds. Mind you this pulse
width agrees with the Centronics Parallel Interface Protocol (since only a min-
imal time is specified), but is too long for a few printers. I have optimized
the code that loads the PSG chip with a character and flashes the strobe (only
four assembly instructions long). This decreases the STROBE pulse width to
1.5 to 2 microseconds (a limitation of the PSG chip, not the 68000 CPU), small
enough to make a big difference! Now all the TI 880 and 885 printers work
perfectly fine with the ST computer IF YAPS IS INSTALLED FIRST BEFORE PRINTING.
The TI 810 printers are apparently more finicky unfortunately. One out of two
printers that I have at my office works fine. The other will duplicate 1 char-
acter out of 20,000 characters (yes, that's twenty thousand) sent to it on the
average. This patch is not perfect, but darn well tries to be so. And at least
with YAPS_T.PRG installed I estimate that with YAPS installed you can use more
than 99% of Centronics compatible printers currently available on the market!