[sane-devel] Canon_pp freezes halfway

[Matthew Duggan]

Hi there!

On 29/11/2006, at 11:22 AM, selma kapetanovic wrote:
...
> I am running
> ..
> * Parallel port is in EPP mode (BIOS setting)

I'll get back to this...

> It scans most often (not always) in black and white. For color mode  
> the number of "reads" varies from two to four.

Hmm.. that's quite weird, but I'm guessing it's just the increased  
amount of data in colour mode.

> I spent quite some time trying to make it work. Should I have known  
> it takes so much time, I would toss the scanner in the garbage.
> At this point it is more of a challenge. I know that I am not the  
> only person who has the problem and I want to post the solution to  
> the Ubuntu web site along with a recommendation not to buy canon  
> scanners.

Well, I'm probably not telling you anything you don't know, but it's  
not so much the scanner as the port.

Parallel ports are flakey things - it's amazing they ever work  
really.  They're just not really designed to push the large amounts  
of data scanners need to move.

> ...
> [canon_pp] detect_mode: Port supports ECP-H.
> [canon_pp] detect_mode: Port supports interrupts
...

So according to the probing done by libieee1284, the port supports  
ECP-H transfers and interrupts, but no mention of DMA.  Generally  
speaking I've had the most success in the past using ECP and DMA mode  
or pure software mode, but pure software is very slow and nasty - DMA  
is much preferred if you can get it working.

Anyway, I think the first thing to try is setting the BIOS setting to  
"ECP+EPP" if it has such an option, instead of "EPP".  After that you  
should maybe allocate a fixed IRQ to the parallel port (yes, I know,  
plug&play - but it's just more reliable this way!).  Once you've done  
that you can try playing with the parport_pc module settings to try  
and get DMA transfers working.  I wish there was an easier way, but  
that's pretty much it.

Hope that helps!

Cheers,

- Matthew