How can I access a DDC/CI Display Dependent Device from a Windows application?

Question

I am modifying a monitor controller for a prototype. It would be convenient to send commands to the prototype using DDC/CI. In Windows, I can't find an obvious way to send a DDC/CI command to a "display dependent device".

The Monitor Configuration API can send virtual control panel commands, but it does not give access to display dependent devices (which would have an I2C address other than 0x6e).

Nicomsoft's WinI2C/DDC product seems to give access to a display dependent device, but it is end-of-life. I would prefer not to build a dependency on an end-of-life product.

NVIDIA's NVAPI has an I2C API, but I would like a solution that also works with Intel and AMD graphics adaptors.

Answer 1

A solution exists for windows which respect XDDM driver display model. Windows 8 and 10 use WDDM.

In XDDM there is a windows O.S. supplied video port driver, and the hardware vendor supplies a miniport driver. When the miniport driver call's the video port driver's edid helper api (VideoPortDDCMonitorHelper), the miniport must supply 4 i2c function pointers as arguments.

In order to utilize these interfaces however you must be acting as the video port driver. So you have to write a video port lower filter driver which just passes along all the interfaces on from the windows supplied video port driver to the miniport driver. Hook the api's and export them to a usermode driver or ioctl which an application can call.

It may be possible to simply mount an instance of the miniport driver and some how get it to call VideoPortDDCMonitorHelper. But with out the help of the actual video port driver it would be difficult to get guidance on how to do that. Also you would have 2 instances of the driver running which may be against the rules for windows.

It does not appear this solution works for windows 8 and 10 because they use a different display driver model which doesn't appear to expose low level control of i2c. It is internal to the miniport driver.