[sane-devel] sane_cancel on HP 5590

[Ilia Sotnikov]

On Tue, Feb 26, 2008 at 9:41 PM, m. allan noah <kitno455 at gmail.com> wrote:
> sane_cancel is meant to be called asynchronously, so it probably
>  should not send any commands to the scanner.
>  sane_read should probably check a 'no longer scanning' flag, and do
>  whatever cleanup is required.
>
>  take it away Ilia :)

I agree, the sane_cancel() function from the backend doesn't fully
conform to SANE standard - it tries to send cancel command to the
scanner IMMEDIATELY.

>  >  I am trying to cancel a page scan. so i call sane_cancel while
>  >  scanning is in progress
>  >  but the application get stuck on the next sane_read,
>  >  instead of return SANE_STATUS_CANCELLED
>  >

Fixing the synchronous nature of the backend's sane_cancel() function
could make the whole picture cleaner and should be done to follow the
SANE standard. However, while experimenting with the scanner I noticed
that it's very sensitive to data reading. When only partial data was
read from the device and a command
then sent to it the device was hanging in most cases.

At this moment, you should avoid calls to sane_cancel() while working
with such a scanner. Or, if that's somewhat urgent for you, I could
prepare the patch.

I think that device internals is rather simple in terms of
functionality to reduce production prices. The same decision could be
made from looking to the command set and to the absence of paper
sensor on the ADF unit. That said, office / workgroup HP scanning
devices are not perfect from technical point of view.

-- 
 Ilia Sotnikov