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<TITLE>sane-devel: Re: Problems with Acer ScanPrisa 640S</TITLE>
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<META NAME="Author" CONTENT="Sebastien Sable (sebastien.sable@gmx.net)">
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<META NAME="Subject" CONTENT="Re: Problems with Acer ScanPrisa 640S">
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<H1>Re: Problems with Acer ScanPrisa 640S</H1>
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<!-- received="Sat Oct 21 08:02:59 2000" -->
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<!-- sent="21 Oct 2000 17:12:17 +0200" -->
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<!-- name="Sebastien Sable" -->
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<!-- email="sebastien.sable@gmx.net" -->
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<!-- subject="Re: Problems with Acer ScanPrisa 640S" -->
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<!-- id="87pukuxm7i.fsf@gmx.net" -->
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<!-- inreplyto="Fri, 20 Oct 2000 20:08:52 -0700"" -->
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<STRONG>From:</STRONG> Sebastien Sable (<A HREF="mailto:sebastien.sable@gmx.net?Subject=Re:%20Problems%20with%20Acer%20ScanPrisa%20640S&In-Reply-To=<87pukuxm7i.fsf@gmx.net>"><EM>sebastien.sable@gmx.net</EM></A>)<BR>
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<STRONG>Date:</STRONG> Sat Oct 21 2000 - 08:12:17 PDT
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<P>
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<LI><STRONG>Next message:</STRONG> <A HREF="0242.html">Peter Kirchgessner: "Re: Patches for sanei_debug.h/sanei_init_debug.c and the HP-backend"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0240.html">abel deuring: "Re: Problems with Acer ScanPrisa 640S"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0219.html">cbagwell@sprynet.com: "Re: Re: Problems with Acer ScanPrisa 640S"</A>
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<LI><STRONG>Maybe reply:</STRONG> <A HREF="0219.html">cbagwell@sprynet.com: "Re: Re: Problems with Acer ScanPrisa 640S"</A>
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<P>
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"Lawrence Glaister" <<A HREF="mailto:lg@jfm.bc.ca?Subject=Re:%20Problems%20with%20Acer%20ScanPrisa%20640S&In-Reply-To=<87pukuxm7i.fsf@gmx.net>">lg@jfm.bc.ca</A>> writes:
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<BR>
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<P><EM>> I am wondering if the speed test can be removed.... what does it
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</EM><BR>
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<EM>> really get used for? Since there is probably only a 3-1 range in
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</EM><BR>
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<EM>> times between the slowest and fastest scanners, does the rate really
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</EM><BR>
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<EM>> need to be measured... it doesn't seem to get used for setting
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</EM><BR>
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<EM>> timeouts.
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</EM><BR>
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<P>My scanner is probably very slow compared to others (it's 4 years
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<BR>
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old). But even with this slow scanner, I can always put
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<BR>
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expected_read_bytes to its maximum value without any problem. So the
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<BR>
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speed test is probably useless (at least up to 300dpi with scsi
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<BR>
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scanners).
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<BR>
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<P><EM>> Do you notice your scanner blocking during the speed test or during a real
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</EM><BR>
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<EM>> scan? I found a "hang condition" was occurring during the speed test because
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</EM><BR>
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<EM>> RGBRouter was called with a small 32k buffer to test the transfer rate with.
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</EM><BR>
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<P>My scanner was only blocking during the real scan with a picture of
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<BR>
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more than about 400KB. I am going to try to describe it more
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<BR>
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precisely:
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<BR>
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<P>when the scan starts, the first value of expected_read_bytes just
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<BR>
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before scsi_read in SCSISource_get is the maximum value (~32000 or
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<BR>
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something).
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<BR>
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Then nearly each time a new scsi_read happens expected_read_bytes is
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<BR>
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decreased of about 2000. This reduction happens in the calculation of:
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<BR>
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ps->pss->expected_read_bytes =
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<BR>
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((int) (msecs/ps->pss->ms_per_line))*ps->pss->bytes_per_line;
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<BR>
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<P>So while scanning, you have the number of bytes read at each step:
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<BR>
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step1: 32000
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<BR>
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step2: 30000
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<BR>
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step3: 28000
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<BR>
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...
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<BR>
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step15: 4000
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<BR>
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step16: 2000
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<BR>
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step18: 0
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<BR>
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step19: 0
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<BR>
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...
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<BR>
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<P>Of course, if you arrive at step 18, you ask for nothing, so you get
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<BR>
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nothing and the scan just starts an infinite loop asking nothing to
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<BR>
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the scanner... eheh -> problem
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<BR>
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<P>This happens if your picture is bigger than :
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<BR>
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(32000 + 30000 + 28000 + .... + 4000 + 2000) = ~400KB
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<BR>
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<P>(my old math teachers would kill me for such a line! I said it was
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<BR>
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_about_ 32000)
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<BR>
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<P>If I force expected_read_bytes to be always the maximum value, the
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<BR>
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scanner works perfectly.
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<BR>
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<P><EM>> The rest of the code was expecting a 23mb image to be scanned and the
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</EM><BR>
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<EM>> RGBRouter_remaining() function broke with -ve return values.
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</EM><BR>
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<EM>> The second problem I noticed was the EAGAIN problem with the USB driver.
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</EM><BR>
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<EM>> Somewhere in the 2.4.0 code, the USB drivers stopped blocking on a read and
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</EM><BR>
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<EM>> started returning EAGAIN and 0 bytes when the scanner was busy (noticeable
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</EM><BR>
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<EM>> during scanhead backtracking).
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</EM><BR>
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<P>I tried your patches when you suggested them. They didn't change
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<BR>
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anything with my scanner (and didn't appear in the debug info). I
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<BR>
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think that those problems (-ve in RGBRouter_remaining and EAGAIN)
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<BR>
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never happen in my case (it is probably USB specific?).
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<BR>
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<P>Indeed I just tried a 24.8MB picture (full A4 with 300dpi color) and
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<BR>
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everything worked fine.
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<BR>
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<P>A+
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<BR>
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<PRE>
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--
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S<EFBFBD>bastien Sabl<62>
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<A HREF="mailto:sebastien.sable@gmx.net?Subject=Re:%20Problems%20with%20Acer%20ScanPrisa%20640S&In-Reply-To=<87pukuxm7i.fsf@gmx.net>">sebastien.sable@gmx.net</A>
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<P>--
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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:%20Problems%20with%20Acer%20ScanPrisa%20640S&In-Reply-To=<87pukuxm7i.fsf@gmx.net>">majordomo@mostang.com</A>
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</PRE>
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<LI><STRONG>Next message:</STRONG> <A HREF="0242.html">Peter Kirchgessner: "Re: Patches for sanei_debug.h/sanei_init_debug.c and the HP-backend"</A>
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<LI><STRONG>Previous message:</STRONG> <A HREF="0240.html">abel deuring: "Re: Problems with Acer ScanPrisa 640S"</A>
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<LI><STRONG>Next in thread:</STRONG> <A HREF="0219.html">cbagwell@sprynet.com: "Re: Re: Problems with Acer ScanPrisa 640S"</A>
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<LI><STRONG>Maybe reply:</STRONG> <A HREF="0219.html">cbagwell@sprynet.com: "Re: Re: Problems with Acer ScanPrisa 640S"</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>Sat Oct 21 2000 - 08:06:16 PDT</EM>
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