[sane-devel] Canon Mx 700 - Scanbuttons

[m. allan noah]

> I finally found some time to dig into the backend to see what it does
> and how to use it (too many other things to do and been ill for a
> while). I now understand how things work.
>
> The button-1 and button-2 options are set when sane_control_option() is
> called for option button_update with action SANE_ACTION_SET_VALUE.
> SANE_ACTION_SET_VALUE button_update is used to poll the scanner and set
> button-1 and button-2. But scanbd does not support
> SANE_ACTION_SET_VALUE.
>

The sane standard does not really cover the proper implementation of
buttons, but I would say that the mechanism you described is weird,
and should be changed. Reading the value of the button should do
whatever is required to get the value from the scanner. It should not
be required to set another option to update the value of the button.
In the case where the value for all buttons is requested in one
command to the scanner, the backend should cache the values as
required. The fujitsu backend uses this scheme, perhaps the code could
be adapted.

allan
-- 
"The truth is an offense, but not a sin"