Mark Bixby ([log in to unmask]) wrote:
: We're contemplating upgrading to networked JetDirect EX printers of both the
: laser and impact variety.  I know MPE/iX 5.5 will have HP support for
networked
: printers, but I can't wait for 5.5.
 
: What I need to know is, how do the various 3rd party spooling products handle
: paper jams for networked impact (i.e. LPQ 1200) printers?  Say I'm 500 pages
: into a monster report and a paper jam munches several pages.  Can I
"backspace"
: similar to SPOOLER ;RESUME;OFFSET=-pagecount, or am I stuck with reprinting
: from the beginning?  Note that the spoolfile may have critical escape
sequences
: at the beginning to establish fonts, etc.
 
Perhaps it would be worthwhile excerpting in this space some topics I
expounded on in some detail several months ago.
 
No host spooler, HP's or 3rd party, can reliably restart at a given page
(other than the beginning) without support in the printer itself.  This
support is two-pronged:
o   The printer must be able to report completion of each page to the host
    as it occurs, or at least, on request.
o   The printer must be able to accept and interpret (but not print) data
    which precedes the target page, the page at which printing is to start.
    This is called "silent-running".
 
With only these properties, you can start printing at any page of the report
you like, although you are forced to silent-run from the beginning of the
spool file (to get the "critical escape sequences" Mark referred to).
This technology has been supported since the first release of the HP2680
page printer.
 
HP256x HP-IB (CIPER) printers went one better -- they returned environmental
snapshots called "checkpoints" at the end of each page.  With a few
exceptions, this allowed the HP spooler to download the checkpoint to the
printer in a recovery situation, then start transmitting from that point
instead of the beginning.  This greatly shortened the silent-running time.
 
The important point is the printer co-operation.  Without it, there is no
way to reliably restart output at the page you want and with the environ-
ment you want.  You can come close by building a complete printer emulator
in your spooler -- one that knows every control sequence of your target
printer.  This is an enormously difficult undertaking, in part because it
is non-flexible -- different printers may incorporate different options
(for example, PostScript or no PostScript).  The same interpreter may not
work on more than one printer without massive (and complex) configuration
options.  It would also be very slow.
 
But even the best emulator does not know some exact printer definitions.
What size paper is in the tray?  What printer defaults (font, LPI) exist,
so that the output does not have to (and may not) set them.  If you
try to recover-by-emulation an 8 LPI file which does not explicitly set
8 LPI file because the creator of the file "knew" the printer was set
to 8 LPI by default -- if you try to recover such a file using 6 LPI
emulation, you will not do so correctly (unless page breaks are explicitly
specified, and each page has no more than 60 lines on it).
 
Enough of that.  To answer Mark's unasked question about the LPQ 1200
printers, they do not have the required support I mentioned earlier.
Therefore, jam recovery consists of:
o   Reprinting the entire file, which Mark wishes to avoid,
o   Creating a subset spool file (say, with SPIFF APPENDs) and printing
    that.
o   Some sort of manual intervention similar to what he described for
    Quest's NBSPOOL product.
 
We've requested the needed support from the printer division, but since
it's an OEM'ed product it has to go through an additional layer.  No word
yet on whether future impact printers will support page level recovery,
and if so, when.
 
Hope this helps.
 
-Larry "MPE/iX Spoolers 'R' Us" Byler-