Problem printing w/ raw printers on SCO Openserver 6

[Nelson Neves]

> Hi,
>
> Generic description:
>
> At the place I work on, it was decided to migrate from SCO Openserver 5.x to Openserver 6.0 MP2, which is now at work. The decision was taken based on the applications the OS is supporting, to facilitate the migration.
>
> Nonetheless, the printing system was a bit on the old side, with lots of hammered filters and we decided to implement Cups (version 1.1.21), as it is distributed with the current Openserver release.
>
> The printers used before kept being used, some 8 Epson printers, from the old LQ-570 to the recent 590. All of them are used as serial printers, connected to a Perl IOLAN STS w/ 8 RS-232 ports (4800, 8N1). We also added a new Epson A3 size (don't remember the model) as a USB system printer (default).
>
> We configured Cups, added the printers, configured as raw (the application on the server controls the printing since the dawn of times) and everything seemed to be working fine. Our joy wouldn't last long.
>
> Problem description:
>
> The first time the users reported the problem, we assumed it was an application error, which at the time made some sense, since the consequence of the problem was the skipping of pages on a long listing, eg.: it printed from page 1 to page 5 and then jumped to page 7, skipping page 6. This should be consistent to an application problem, but we started noticing that it was random, meaning that it happened on a random basis. It could happen on page 3, 5, 16, whatever. We also noticed that not only pages skip, but lines also, so we turned our eyes to buffering problems.
>
> The idea of buffer problems came as soon as we noticed that printing to a new Epson LQ-590, the problem wouldn't happen. Main difference from this to the other printers? Buffer memory. The printer has enough memory to engulf the whole spooled file first and it then starts printing. We can actually see that it's slower than the others on the print job start, but it finishes them and it doesn't skip a page or a line. All of the other printers start printing almost immediatly, as soon as the file is spooled.
>
> Now, you could say that it is a problem of the IOLAN and of the old printers, their shortness of buffer memory, etc., but don't forget that all of this was already fully working with the old printing system, on the Openserver 5.x, and this situation only started happening when we changed to Cups.
>
> I believe the situation is identified, but I don't have any idea on how to customize the buffering on Cups, meaning, how to prevent the "dumping" of all the information directly to the print server/printers, instead of small chunks of data, as it should do.
>
> At the moment, the users were advised to restrain the length of their listings (and they are heavy printer users, due to the enterprise type), but this is not a solution, of course.
>
> Any ideas/opinions are most welcome.
>
> TIA,
> Nelson Neves


I forgot to mention that the above described problem also happens with the USB connected printers.

TIA,
Nelson Neves