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Date:      Tue, 10 Mar 1998 15:18:55 -0500 (EST)
From:      Peter Dufault <dufault@hda.com>
To:        robsch@robkaos.ruhr.de (Robert Schien)
Cc:        freebsd-scsi@FreeBSD.ORG
Subject:   Re: Scanner support
Message-ID:  <199803102018.PAA22926@hda.hda.com>
In-Reply-To: <m0yCSrt-000695C@robkaos.ruhr.de> from Robert Schien at "Mar 10, 98 06:31:09 pm"

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> I set the symlink
> ln -s uk0 scanner
> 
> But when I invoke scanimage I get the following message:
> Mar 10 18:20:11 robkaos /kernel: uk0: physio split the request.. cannot proceed
> Mar 10 18:20:11 robkaos /kernel: uk0: physio split the request.. cannot proceed
> 
> Did I anything wrong? There isn't much FreeBSD specific documentation
> in the sane package :-(

The user level commands don't know how to repackage a command when
it is split up due to the memory not being physically contiguous
- it doesn't know the details of the commands so it can't do the
split properly.  This makes it bad for data transfers.

Options (if available) are to configure sane to use read/write
transfers to some device instead for the data transfer, to set it
to use smaller block sizes (4K will always work), or a questionable
idea involving hackery to map a buffer to a contiguous address
using mmap.

I thought once about configuring the read/write details for the uk
device - there aren't many flavors and a few "set transfer style
1", "set transfer style 2" calls would fix this so you could then
have a read/write entry point, but I went no farther than thinking
about it.  The appropriate use for uk is IMHO for device setup,
quirky commands, poking investigating how a device works, etc.

Peter

-- 
Peter Dufault (dufault@hda.com)   Realtime development, Machine control,
HD Associates, Inc.               Safety critical systems, Agency approval

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