# Success in decreasing backtrackrate on mustec 1200sp in color mode

Rainer krienke (krienke@mailhost.uni-koblenz.de)
Sun, 07 Sep 1997 17:27:26 +0200

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>Rainer Krienke wrote:
><<> =

>> | From fnevgeny@plasma-gate.weizmann.ac.il Sun Aug 31 23:45:11 >19=
97
<> | From: Evgeny Stambulchik <fnevgeny@plasma-gate.weizmann.ac.il>
>> | Date: Mon, 1 Sep 1997 00:39:30 +0300 (IDT)
>> | To: krienke@informatik.uni-koblenz.de
>> | Subject: Re: Backtracking in color scanning
>> | MIME-Version: 1.0
>> | =

>> | Rainer krienke <krienke@mailhost.uni-koblenz.de> wrote:
>> | > =

>> | > I use sane0.62 with my mustek 1200spro (connected to an >ADAPT=
EC 2940
>> | > scsi adapter).
>> | =

>> | Do you mean Paragon 1200SP Pro? How did you manage to make it >wo=
rk with =

>> sane??
>> | =

<> =

>> Oh sorry I was "some letters" wrong. I did'nt mean 1200 Spro but >must=
ek 1200 SP.
>
>> Because of the assumption of Roger (R.E.Wolff@BitWizard.nl ) who
>> said the backtracking problem might be due to the kernel buffer that
>> has to be copied in user space, I thought that if this is true
>> something should change if I reduce the buffer from 127K to half the

>I just use a 1Mb buffer for my scanner. However I had to change a few
>lines in sg.c ...... Ah. I nowadays have the patch ready. Attached. =

>
>Your "kernel data segment" does grow by a megabyte using this
>patch.... I'm going to submit a slightly more generic patch one
>day......

>Using half the size, or even a quarter (32k, default) doesn't help.

>We could try to issue the next "read" AS FAST AS POSSIBLE, discarding
>the data just read. This probably requires some serious hacking. =

>> size. I recompiled sane and my kernel but the effect when scanning
>> colour images stayed the same. Moreover I think because of the fact
>> that other people (running Pentium 200 pro maschines) have the same
>> problem this cannot be due to lack of speed.

>A pentium PRO is not much faster on memory limited copies than a
>pentium. (Both use a 64bit main memory link.)
>
>
> Roger.

Thanks for your patch that was includes in your mail above. Sorry I did
not have the time until now to give it a try.

Well increasing the buffer size in sg.h to a size of 0x100000 really
helped. The effect that there was too much bacjtracking when scanning a
color image at say 300dpi has gone. The scantime improved a lot by this.
It=B4s now comparable to the time a windows twain driver needs to do the
same.

Thanks =

Rainer =

----------------------------------------------------------------------
Rainer Krienke krienke@informatik.uni-koblenz.de
Universitaet Koblenz, http://www.uni-koblenz.de/~krienke
Rechenzentrum, Voice: +49 261 9119-641
Rheinau 3-4, 56075 Koblenz, Germany Fax: +49 261 9119-499
----------------------------------------------------------------------

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