Originally Posted by
Unwinder
A few tips and tricks:
1) Once you've determined index of I2C bus containing VRM on some display adapter (e.g. I2C bus 3 on GTX 200 series), the same index can be safely used on the same display adapter model by others. Display adapters have a few I2C buses assigned for differed functions (e.g. for connecting DDC and for external devices like VRMs, thermal sensors, fan PWM controllers and for on), VRM's I2C bus is defined by PCB design so it is fixed for the same display adapter families.
2) Don't try to scan more I2C buses than the GPU actually has (there was some posting with attempt to scan buses 0-99 in hope to find VRM on G92). Each GPU architecture supports fixed number of I2C buses, e.g. G80 and newer GPUs have only 4 I2C buses, pre-G80 supports 3 buses, pre GF4 supports just 2 buses and so on.
3) I see that many users started to enable VT1103 plugin now. Please pay attention to the following info from RivaTuner's release notes and always remember about it when using this plugin:
"Please take a note that Volterra voltage regulators are rather sensitive to frequent polling and may return false data under heavy load, so it is not recommended to use VRM monitoring in daily monitoring sessions"
4) There were some questions about finalizing these new VRM settings in NVIDIA VGA BIOS. You cannot use Nibitor for that because the tool knows nothing about VRMs and works with BIOS voltage tables only, it is only allowing you to change associations between performance levels (i.e. 2D/3D modes) and 4 fixed voltages stored into VRM registers 15-18 by default. However, you can easily edit your BIOS with any hex editor to reconfigure initialization scripts writing these 4 fixed voltages to VRM during POST. It is rather simple task, taking my 65nm EVGA GeForce GTX 260 as example the following script command in VGA BIOS is configuring VT1165:
4D 80 E0 06 15 3B 16 31 17 36 18 2F 1D 55 19 01
The command uniquely identifies I2C serial byte write operation, encodes target I2C device address (E0 is 8-bit encoding of VT1165's 7-bit address 70 including read/write flag in the first bit), tells script processor how many bytes have to be written (06) and finally defines register addressed and data to be written to each register (register 15 -> 3B, register 16 -> 31 and so on).
The voltages can be different for different VGA BIOS images, so the easiest way to locate this command in any GTX200 BIOS image is to search for 4D 80 E0 byte chain.
