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<TITLE>sane-devel: Re: snapscan</TITLE>
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<META NAME="Author" CONTENT="Henning Meier-Geinitz (hmg-ml@gmx.de)">
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<META NAME="Subject" CONTENT="Re: snapscan">
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<H1>Re: snapscan</H1>
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<!-- received="Wed Jan 10 12:30:06 2001" -->
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<!-- sent="Wed, 10 Jan 2001 20:17:04 +0100" -->
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<!-- isosent="20010110191704" -->
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<!-- name="Henning Meier-Geinitz" -->
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<!-- subject="Re: snapscan" -->
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<!-- id="20010110201704.A646@vortex.swb.de" -->
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<!-- inreplyto="200101101021.LAA02078@siegel.math.uni-frankfurt.de" -->
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<STRONG>From:</STRONG> Henning Meier-Geinitz (<A HREF="mailto:hmg-ml@gmx.de?Subject=Re:%20snapscan&In-Reply-To=<20010110201704.A646@vortex.swb.de>"><EM>hmg-ml@gmx.de</EM></A>)<BR>
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<STRONG>Date:</STRONG> Wed Jan 10 2001 - 11:17:04 PST
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<P>
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<LI><STRONG>Next message:</STRONG> <A HREF="0117.html">abel deuring: "Re: SANE and Linux kernel 2.4.0"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0115.html">Rene Rebe: "Re: help - hp 5300c"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0109.html">Christian Nassau: "snapscan"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0147.html">Christian Nassau: "Re: snapscan"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0147.html">Christian Nassau: "Re: snapscan"</A>
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<P>
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Hi,
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<BR>
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<P>On Wed, Jan 10, 2001 at 11:21:03AM +0100, Christian Nassau wrote:
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<BR>
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<EM>> *** Remarks on blocking/non-blocking mode
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</EM><BR>
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<EM>>
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</EM><BR>
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<EM>> There seems to be some confusion or unclarity what one
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</EM><BR>
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<EM>> should mean by these terms. Note that the SANE specs
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</EM><BR>
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<EM>> don't say anything about it!
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</EM><BR>
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<P>The standard defines the meaning of blocking/non-blocking mode in
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<BR>
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chapter 4.3.10 (sane_read). Blocking/non-blocking describes the
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<BR>
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behaviour of sane_read in the case that no data is available. In
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<BR>
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blocking mode sane_read will wait until at least one byte is available
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<BR>
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(it "blocks"). In non-blocking mode it returns immediately (len=0).
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<BR>
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<BR>
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<EM>> -- blocking mode (aka *strongly* blocking mode):
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</EM><BR>
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<EM>> all of the data is fetched from the scanner (in the
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</EM><BR>
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<EM>> first call to sane_read), then handed over to the frontend
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</EM><BR>
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<EM>> in digestable pieces
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</EM><BR>
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<P>No blocking or non-blocking involved. It's completely up to the
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<BR>
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backend how it gets data from the scanner. Most backends start a
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<BR>
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reader process in sane_start and have some way of buffering data.
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<BR>
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<P><EM>> -- simulated non-blocking mode:
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</EM><BR>
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<EM>> program runs in strongly blocking mode but asks
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</EM><BR>
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<EM>> only for a convenient amount of data,
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</EM><BR>
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<EM>> data is then handed out to the frontend
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</EM><BR>
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<P>As Oliver said, the backend must provide any amount of data down to
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<BR>
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one byte per read.
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<BR>
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<P><EM>> -- non-blocking mode
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</EM><BR>
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<EM>> program runs in strongly blocking mode (for
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</EM><BR>
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<EM>> the full image), but as a background process
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</EM><BR>
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<P>For blocking/non-blocking (from the SANE point of view) it's
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<BR>
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unimportant how the data was transmitted from the scanner to the
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<BR>
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backend. The backend may use 32 k buffers and wait until each buffer
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<BR>
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is transmitted to the frontend, use double buffering, or read all data
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<BR>
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from the scanner into one big buffer before returning the first byte
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<BR>
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through sane_read.
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<BR>
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<P>Bye,
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<BR>
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Henning
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<BR>
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<P><PRE>
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--
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Source code, list archive, and docs: <A HREF="http://www.mostang.com/sane/">http://www.mostang.com/sane/</A>
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To unsubscribe: echo unsubscribe sane-devel | mail <A HREF="mailto:majordomo@mostang.com?Subject=Re:%20snapscan&In-Reply-To=<20010110201704.A646@vortex.swb.de>">majordomo@mostang.com</A>
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</PRE>
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<!-- next="start" -->
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<LI><STRONG>Next message:</STRONG> <A HREF="0117.html">abel deuring: "Re: SANE and Linux kernel 2.4.0"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0115.html">Rene Rebe: "Re: help - hp 5300c"</A>
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<LI><STRONG>In reply to:</STRONG> <A HREF="0109.html">Christian Nassau: "snapscan"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0147.html">Christian Nassau: "Re: snapscan"</A>
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<LI><STRONG>Reply:</STRONG> <A HREF="0147.html">Christian Nassau: "Re: snapscan"</A>
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<EM>
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This archive was generated by <A HREF="http://www.hypermail.org/">hypermail 2b29</A>
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: <EM>Wed Jan 10 2001 - 12:33:08 PST</EM>
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