# Re: Writing Fujitsu M3091 backend

From: mh (crapsite@gmx.net)
Date: Thu Mar 01 2001 - 07:24:39 PST

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  Nick Lamb, Don, 01 Mär 2001 :
  > On Thu, Mar 01, 2001 at 10:34:13AM +0100, mh wrote:
  > > There is no "well known option" or a flag in SANE_Parameters which tells the
  > > frontend that it should continue with image acquisition. Therefore you
  >
  > There is a return code, SANE_STATUS_NO_DOCS which indicates that we've
  > run out of paper, or some analagous problem has occurred, this is what
  > you want I think.

  Yes, I know, and I'm sure it would work this way, *but* it's also a hack:
  A SANE_STATUS_NO_DOCS is an status code and should probably not be abused
  to solve this problem.
  I just made some tests, not with a real ADF scanner but with my test-backend,
  which can simulate all those status codes:
  The graphical frontends normally inform the user, if a sane_read() returns
  SANE_STATUS_NO_DOCS. How can you avoid this, if you're scanning in "duplex"
  mode? Doesn't this mean, that you always get this message when you're using
  this mode? This would be even more confusing, if you have an ADF scanner
  (filled with 100 documents) which can also use the "duplex" mode. And there's
  no chance for the frontend to suppress this message, since it doesn't know about
  it(no well known option). (Or *does* e.g. XSane suppress this message in ADF
  mode?)

  > > have the following possibilities:
  > > -let the user hit the scan button for each single scan operation
  > > -let the user set the number of scans, and then try to acquire this number of
  > > scans.
  >
  > -scan images until the backend returns SANE_STATUS_NO_DOCS indicating
  > that it doesn't have anything left worth scanning.

  This means, that the user must set the frontend to some "special" ADF
  mode and activate the "duplex"-option or how does the frontend know, that it
  should continue scanning 'til SANE_STATUS_NO_DOCS?
  E.g. for XSane it would mean, that you have to open the settings menu, open
  the configuration dialog, choose ADF source just to get the two images?
  BTW can one use the ADF mode in XSane without having an ADF?

  > This is what all the existing software which supports ADF does AFAIK.
  > Some future version of the standard should spell this out in the advice
  > for implementers.

  Well, I never understood, why ADF should mean: "scan all documents".
  (even if it might be useful in some/most situations)
  There might be persons that put 50 documents in there doc feeder and then
  just want to scan 5 or 10, do something with the scans and then scan the next 5
  or 10.

  Waiting for your comments ...
  Michael

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