Howto do i2c communication of videocard and monitor ??

Howto do i2c communication of videocard and monitor ??

[Vishal Soni]

Hi,

  I am trying to communicate to the monitor eeprom to get the
monitor capabilities and for that i need to have SDA/SCL bit positions
in the control word register of the video card (to read and wrtie data
using i2c protocol).

Different video card vendors have different offsets for the control
word register and different bit positions for SDA/SCL.

I tried to use linux exported Symbol "get_EDID_from_firmware" and then
using kgdb to debug the kernel module (that i wrote) to get the same
but failed to find the way to get the above.

I do have the offset of the control word register and Masking Value of
Intel and Matrox card but i would like NOT to hardcode the masking
value and the offset in my code. This will lead me to modify  my code
for the different cards.

Is there any way to get the control word register's address (and then
SDA/SCL bit position) on the linux operating system ?

FYI : Masking Value that i am referring to is the value that has to be
ANDed to the DATA(bit - 0/1) before writing it to Control word
register so that the right bit can be written on to the SDA/SCL lines.

or to sum up ::
How to get SDA/SCL bit position in the control word register of the video card?

Any pointers to this or your guidance would be highly appreciated.

Thank you for your time.
regards,
Vishal.


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Re: Howto do i2c communication of videocard and monitor ??

[Nicolas Boichat]

Hi Vishal,

On Mon, 2006-01-30 at 01:19 +0530, Vishal Soni wrote:
> Hi,
> 
>   I am trying to communicate to the monitor eeprom to get the
> monitor capabilities and for that i need to have SDA/SCL bit positions
> in the control word register of the video card (to read and wrtie data
> using i2c protocol).

You would perhaps be interested in ddccontrol
(http://ddccontrol.sourceforge.net): it controls monitor parameters
(brightness, contrast, etc.) using DDC/CI protocol on the I2C busses of
the graphics card. Maybe you could use this code as a basis.

> Different video card vendors have different offsets for the control
> word register and different bit positions for SDA/SCL.
> 
> I tried to use linux exported Symbol "get_EDID_from_firmware" and then
> using kgdb to debug the kernel module (that i wrote) to get the same
> but failed to find the way to get the above.

I don't think this kind of application should be in the kernel,
ddccontrol works in user-space, either by using /dev/i2c-* devices
provided by most kernel framebuffer drivers, or by writing directly to
PCI memory, when there is no support in the kernel, or when the
framebuffer driver conflicts with proprietary 3D-accelerated drivers
(ATI, nVidia).

I hope this helps.

Best regards,

Nicolas

> I do have the offset of the control word register and Masking Value of
> Intel and Matrox card but i would like NOT to hardcode the masking
> value and the offset in my code. This will lead me to modify  my code
> for the different cards.
> 
> Is there any way to get the control word register's address (and then
> SDA/SCL bit position) on the linux operating system ?
> 
> FYI : Masking Value that i am referring to is the value that has to be
> ANDed to the DATA(bit - 0/1) before writing it to Control word
> register so that the right bit can be written on to the SDA/SCL lines.
> 
> or to sum up ::
> How to get SDA/SCL bit position in the control word register of the video card?
> 
> Any pointers to this or your guidance would be highly appreciated.
> 
> Thank you for your time.
> regards,
> Vishal.




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