[Q] ov7670: green line in VGA resolution

[Q] ov7670: green line in VGA resolution

[javier Martin]

Hi,
I am currently testing an ov7670 sensor against my mx2_camera.c
soc-camera driver. Everything works as expected with the exception of
a green vertical line of about 6-7 pixels width that appears on the
left side of the image.

I suspect the problem is related to the fact that this sensor has an
array of 656 x 488 pixels but only 640 x 480 are active. The datasheet
available from Omnivision (Version 1.4, August 21, 2006) is not clear
about how to configure the sensor not to show non active pixels but I
could find the following patch which addresses a similar problem for
QVGA:

http://kernel.ubuntu.com/git?p=bradf/backup.ubuntu-maverick/.git;a=commitdiff;h=e4182762eaf3c80b2f5c8d1d373409d7c2843579;hp=e770cc1e35a3f11cffd1f38f52060e3e38b4fbf7

But I don't know how these values can be extrapolated to the VGA case.
Has anybody found the same issue?

Regards.
-- 
Javier Martin
Vista Silicon S.L.
CDTUC - FASE C - Oficina S-345
Avda de los Castros s/n
39005- Santander. Cantabria. Spain
+34 942 25 32 60
www.vista-silicon.com

Re: [Q] ov7670: green line in VGA resolution

[Jonathan Corbet]

On Mon, 19 Mar 2012 17:27:06 +0100
javier Martin <javier.martin@vista-silicon.com> wrote:

> I suspect the problem is related to the fact that this sensor has an
> array of 656 x 488 pixels but only 640 x 480 are active. The datasheet
> available from Omnivision (Version 1.4, August 21, 2006) is not clear
> about how to configure the sensor not to show non active pixels but I
> could find the following patch which addresses a similar problem for
> QVGA:

Interesting...nobody ever sent that patch anywhere where I've seen it.

Anyway, the ov7670 datasheet is not clear on much of anything, and the
things it *is* clear on are likely to be wrong.

The comment in the patch makes it clear how this was worked out, anyway:
"empirically determined."  Unless you can get through to the one person at
OmniVision who knows how this sensor actually works, the best that can be
done is to mess with the values for the window.  That's often done at both
the sensor and the controller level - if you look at the Marvell
controller, you'll see window tweaking there too.

jon

Re: [Q] ov7670: green line in VGA resolution

[javier Martin]

Hi Jonathan,
thank you for your attention.

On 19 March 2012 18:44, Jonathan Corbet <corbet@lwn.net> wrote:
> On Mon, 19 Mar 2012 17:27:06 +0100
> javier Martin <javier.martin@vista-silicon.com> wrote:
>
>> I suspect the problem is related to the fact that this sensor has an
>> array of 656 x 488 pixels but only 640 x 480 are active. The datasheet
>> available from Omnivision (Version 1.4, August 21, 2006) is not clear
>> about how to configure the sensor not to show non active pixels but I
>> could find the following patch which addresses a similar problem for
>> QVGA:
>
> Interesting...nobody ever sent that patch anywhere where I've seen it.
>
> Anyway, the ov7670 datasheet is not clear on much of anything, and the
> things it *is* clear on are likely to be wrong.
>
> The comment in the patch makes it clear how this was worked out, anyway:
> "empirically determined."  Unless you can get through to the one person at
> OmniVision who knows how this sensor actually works, the best that can be
> done is to mess with the values for the window.  That's often done at both
> the sensor and the controller level - if you look at the Marvell
> controller, you'll see window tweaking there too.

So, what I understand is that you see the same green line and, due to
the lack of documentation for the ov7670, you solve it adjusting de
video window in the Marvell controller driver. Could you confirm this?

Regards.
-- 
Javier Martin
Vista Silicon S.L.
CDTUC - FASE C - Oficina S-345
Avda de los Castros s/n
39005- Santander. Cantabria. Spain
+34 942 25 32 60
www.vista-silicon.com

Re: [Q] ov7670: green line in VGA resolution

[Jonathan Corbet]

On Tue, 20 Mar 2012 09:42:55 +0100
javier Martin <javier.martin@vista-silicon.com> wrote:

> So, what I understand is that you see the same green line and, due to
> the lack of documentation for the ov7670, you solve it adjusting de
> video window in the Marvell controller driver. Could you confirm this?

I wrote that driver quite a few years ago and do not remember the exact
process.  I do remember, though, that making new modes work generally
involved a lot of tweaking on both sides.

jon


Jonathan Corbet / LWN.net / corbet@lwn.net