From: story@sgi.com (David (Duis) Story)
Newsgroups: comp.sys.sgi
Subject: Re: SCSI printers
Date: 21 Dec 92 21:35:49 GMT
Organization: Silicon Graphics, Inc.

In article <34764@adm.brl.mil> karron@karron.med.nyu.edu (Dan Karron (karron@nyu.edu)) writes:
>
>Does anyone have experience with connecting a ps printer to SGI
>boxes via the SCSI {1,2} bus ?

Not a true PS printer, there aren't any I'm aware of that transfer PS
via the SCSI port.

>I have a zippy Xante ps printer. It is quite fast, and I have
>it connected via a centronics port. I have a breakout box on the
>line, and I see lots of handshake activity. I think that the
>printer is out pacing the parallel port on large bitmap images.
>The printer ready line is can be trapped with no data on the data lines.

There shouldn't be a way to outpace the port, the handshaking is
designed to prevent that.  That is, the printer asserts BUSY when it
cannot receive data, and the host doesn't ship a bit out until BUSY is
deasserted.  

>This wonderprinter has a SCSI port, and is designed for direct connection
>to Apple machines. 

According to what spec?  It may emulate a laserwriter IISC, which
isn't a PostScript printer, it just accepts bitmaps.  IF so, there's
an example driver for it in 4DGifts.

>What is the max throughput on the parallel lines ?

I've heard reliable reports of 2MB/sec on an Indigo with the shortest
possible data strobe lengths (see below).  I've personally observed
400+KB/sec on a 4D/25.

I seriously doubt your printer's controller can interpret 24-bit RGB
data at either of those rates.

>What is the bottleneck in getting data out a parallel line ?

Usually it's the printer.

>The CPU wait line shows lots of physical io waiting, like the
>whole CPU wait bar is light blue (whatever that means!).

That means a lot of time is being spent waiting on the printer to
receive the data.  If your printer is the slow link here, not the
host, so a faster transmission path is not going to speed this up.

You might also consider tweaking the strobe lengths, etc..  See 'man
plp' and read the part about PLPIOCSTROBE for more info on shortening
the data strobe lengths.

>What is the throughput on the SCSI 1 or SCSI2 bus ? What are the
>bottlenecks there ?

Peak 5MB/sec, 10MB/sec if you have fast SCSI 2 host (Indigo R4K and
later) and peripheral.

>Would it pay to write/debug a SCSI driver for this beast ? Is there 

From personal experience, probably not.

>lp scripts that talk/listen to the SCSI port ? What are the

No.

>issues to connect a program to a SCSI port ? Kernel drivers ?

You can use the user-level SCSI drivers but your driver will need to
be setuid root to open the /dev/scsi device.  You'll need a copy of
"IRIX Device Driver Programming Guide" (used to be called something
like "Writing Device Drivers for IRIX".)

>I don't know if the printer will try to converse with the host
>via the SCSI port.

It won't, unless you ask it, but that will become clearer if you dig
into it....

SCSI is a fun thing, but I would suggest that you save your time and
tweak the easier parallel port, and spend the (time==$$) you saved on
a newer faster printer.

SGI Hardware Express will be reselling a SCSI-2 printer in January,
the SRS Imager 17D-II: 17ppm, 600x300 dpi, $5995 list price.

That might be a far better investment.

Cheers,

David Story                        	        Silicon Graphics, Inc.
story@bent.wpd.sgi.com				Mountain View, California

I've changed my name, so duis@sgi.com may bounce, please use story@sgi.com.