[pxc] AGC on generic Bt and/or PXC200*

[Alessandro Rubini]

All-To: marius@tbs.co.za,pxc@lists.linux.it Re: [pxc] AGC on generic Bt and/or PXC200*
> From: Marius van Wyk <marius@tbs.co.za>
> To: Alessandro Rubini <rubini@gnu.org>
> Cc: pxc@lists.linux.it
> Subject: [pxc] AGC on generic Bt and/or PXC200*
> Date: Fri, 31 May 2002 12:03:37 +0200

> How do I disable the Auto Gain Control (AGC) on my card?
> (At the moment a generic Bt 878)
> 
> I've figured out that it is bit 6 on the SCLOOP register pair, and am 
> assuming that I only have to switch it off.

This is what pdftotext gives me:

 [6]        RW        0               CAGC
           This bit controls the Chroma AGC function. When enabled, 
    	   Chroma AGC will compensate for non-standard chroma levels. The 
    	   compensation is achieved by multiplying the incoming chroma sig-
    	   nal by a value in the range of 0.5 to 2.0.
    	      0        = Chroma AGC Disabled
    	      1        = Chroma AGC Enabled

Thus, I think this is chroma-related, not luma-related. It doesn't
seem the right parameter to me.

Actually, I've always thought the autogain I see in my 878 device is
the effect of external circuitry.  I'll try to change the adelay
parameter.

BTW: looks like I have a sponsor for per-camera configuration :)

> am not sure where to code it in...

If you want to make experiments, you might try my "phob" driver.  It
exports access to PCI devices so you can set or read hw registers even
if another driver is using it.

Or you can simply use mmap to access high memory, but be careful about
unsigned offsets (i.e., I found that "mapper.c", part of LDD2 sample
code, doesn't work with addresses in the 2G-4G range.  My copy is
fixed, and I think it's high time to release a new version of
ldd2-samples).

/alessandro