[sane-devel] Status of experimental cs3200f back-end

[Lauri Pirttiaho]

Hello,

After a couple of months of other business I have again
some time for hacking the CanoScan 3200F back-end. The
current status is such that I am now working on the
more reliable and safe speed curves and that may take
some weeks to get working. Then I will resume working
on the dark/white shading mechanism.

The reason I decided to do the ramps first is that the
current system is really unsafe. In some cases the
stepping motor will stall at start (too high acceleration)
and the internal position counter, that relies on counting
steps, gets out of sync. Now if the head is moved back
it slams the stopper and I am not really sure if the
HW has been designed to handle that. Therefore for the
safety reasons the accelerations have to be handled so
that the position counter stays in sync.

Another problem currently, seen in the experimental
back-end at 75-dpi is the trace-back acceleration. 
If back tracking is used light horizontal lines appear
in the image. That is due to problems in the back tracking
part of the speed curves and I will try to solve that
too now.

It seems likely that there is some misunderstanding in 
the way I currently use the sanei_usb library. That leads
to problem that in some fast AMD64 machines the firmware
verification fails -- in read-back the scanner NAK's.
I have a stand-alone application that uses directly
the libusb and does the firmware upload and restart
of the scanner. Kristian Fiskerstrand reported that
that application works in his system. If there are
others requiring this temporary fix, please e-mail me.

Then finally a word of warning. The experimental cs3200f
backend is not intended for production use, only for
experimenting and of course for soliciting input to
the development. Therefore, please read the included
cs3200f.txt and the warning in the beginning of that
file, and do not include that back-end to a production
build. In particular do not add cs3200f line to the 
dll.conf unless you are experimenting with this particular
device since it will make the back-end show even if
there is no actual HW, as a dummy device, due to the 
feature used in development. That feature will eventually
be disabled but for now it will be kept there.

With best regards,

Lauri Pirttiaho
Oulu
Finland

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