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<!-- received="Sun Sep 7 05:16:08 1997 MST" -->
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<!-- sent="Sun, 7 Sep 1997 13:53:49 +0200 (MET DST)" -->
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<!-- name="Rogier Wolff" -->
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<!-- email="R.E.Wolff@BitWizard.nl" -->
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<!-- subject="Re: Backtracking in color scanning" -->
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<!-- id="199709071153.NAA03617@cave.BitWizard.nl" -->
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<!-- inreplyto="19970907133054.30337@drawbridge.in-berlin.de" -->
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<title>sane-devel: Re: Backtracking in color scanning</title>
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<h1>Re: Backtracking in color scanning</h1>
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<b>Rogier Wolff</b> (<a href="mailto:R.E.Wolff@BitWizard.nl"><i>R.E.Wolff@BitWizard.nl</i></a>)<br>
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<i>Sun, 7 Sep 1997 13:53:49 +0200 (MET DST)</i>
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<p>
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<ul>
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<li> <b>Messages sorted by:</b> <a href="date.html#143">[ date ]</a><a href="index.html#143">[ thread ]</a><a href="subject.html#143">[ subject ]</a><a href="author.html#143">[ author ]</a>
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<li> <b>Next message:</b> <a href="0144.html">Michael Ritzert: "Re: mustek problems in lineart mode"</a>
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<li> <b>Previous message:</b> <a href="0142.html">Rogier Wolff: "Re: SANE and Mustek MFC-600S"</a>
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</ul>
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<!-- body="start" -->
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Wolfgang Jung wrote:<br>
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<i>> </i><br>
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<i>> It shouldn't be to much work to write a doube buffering sg.o, so </i><br>
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<i>> if activated by some FLAG you could issue a read prior getting the data</i><br>
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<i>> to userspace...(ie: just do another write)</i><br>
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<i>> this should be at least be quick enough to ensure a small set of</i><br>
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<i>> microsseconds between reads.</i><br>
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<p>
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But as David and I were suggesting:<br>
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<p>
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try adding <br>
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if (data_size > 0x1000) return <br>
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<p>
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somewhere in the sg_read, just before the copy of the data from kernel<br>
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to userspace. you don't expect to get an image if you do that, but if<br>
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the scanner stops backtracking, it is worth it to implement the much<br>
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harder double buffering sg.....<br>
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<p>
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<i>> But I could imagine that the scanner itself does the backtracking if </i><br>
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<i>> the read finishes.</i><br>
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<p>
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Correct, so if the above doesn't help, we should look into allowing<br>
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longer "read" commands.<br>
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<p>
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<i>> in Gray mode ie: it does NO backtracking.</i><br>
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<i>> but somehow trows some lines away :(</i><br>
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<p>
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Hmm. Bug in the scanner?<br>
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<p>
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Roger.<br>
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<p>
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<pre>
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--
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** <a href="mailto:R.E.Wolff@BitWizard.nl">R.E.Wolff@BitWizard.nl</a> ** +31-15-2137555 ** <a href="http://www.BitWizard.nl/">http://www.BitWizard.nl/</a> **
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Florida -- A 39 year old construction worker woke up this morning when a
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109-car freigt train drove over him. According to the police the man was
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drunk. The man himself claims he slipped while walking the dog. 080897
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<p>
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<pre>
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--
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</pre>
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<!-- body="end" -->
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<p>
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<ul>
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<!-- next="start" -->
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<li> <b>Next message:</b> <a href="0144.html">Michael Ritzert: "Re: mustek problems in lineart mode"</a>
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<li> <b>Previous message:</b> <a href="0142.html">Rogier Wolff: "Re: SANE and Mustek MFC-600S"</a>
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<!-- nextthread="start" -->
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