I have a problem getting the core voltage I want at both idle and load state. The card in question is the Sapphire Vapor-X HD7950 equipped with two 8 pins contacts. It has a second overclocking bios that can be activated by pushing in a button, and this is what I am using.
What I want
I want the voltage to be low (0.8 V) when idle and at a magnitude of my choice during load (say 1.2 V).
Default settings
With Power limit 0% and not touching the core voltage I have an idle voltage of 0.806 V giving me a total power consumption of my system of about 75 W at a core clock of 300 MHz. Under load it runs at 950 MHz at a voltage of 1.087 V.
Mild OC - Trixx
If I set the core clock to 1100 MHz without touching anything else the card "throttles" and jumps between this target and a lower frequency. So Power limit to the resque: just moving the slider to +20% in Trixx I get a steady 1100 MHz and a steady voltage of 1.087 V. No problem there.
Mild OC + changed voltage - Trixx
This is where it gets complicated. If I change the core voltage to say 1.1 V, nothing happens if I have Power limit (PL) +20%. However, if I lower the power limit the core voltage starts jumping between the set voltage (which is higher than the max voltage at PL=+20%) and a lower value synchronized with the jumps in frequency. The lower I set PL the lower the low voltage is, so at PL = -20% I get huge jumps in voltage.
Locked voltage - Trixx
I tried locking the voltage to avoid these jumps during load. This works, but it has the downside that the voltage does not go down when the GPU is idle. At the default load voltage of 1.087 V the difference vs default idle 0.806 V is about 35 W, and if I increase the voltage further this meaningless waste of energy will just grow. Hence I think locked voltage is a no go.
MSI Afterburner
Changing core voltage in MSI Afterburner has no effect whatsoever unless I force constant voltage, which of course I do not want to do.
I know this must be possible, but the strange interplay between VDCC and Power limit messes it up for me.
What I want
I want the voltage to be low (0.8 V) when idle and at a magnitude of my choice during load (say 1.2 V).
Default settings
With Power limit 0% and not touching the core voltage I have an idle voltage of 0.806 V giving me a total power consumption of my system of about 75 W at a core clock of 300 MHz. Under load it runs at 950 MHz at a voltage of 1.087 V.
Mild OC - Trixx
If I set the core clock to 1100 MHz without touching anything else the card "throttles" and jumps between this target and a lower frequency. So Power limit to the resque: just moving the slider to +20% in Trixx I get a steady 1100 MHz and a steady voltage of 1.087 V. No problem there.
Mild OC + changed voltage - Trixx
This is where it gets complicated. If I change the core voltage to say 1.1 V, nothing happens if I have Power limit (PL) +20%. However, if I lower the power limit the core voltage starts jumping between the set voltage (which is higher than the max voltage at PL=+20%) and a lower value synchronized with the jumps in frequency. The lower I set PL the lower the low voltage is, so at PL = -20% I get huge jumps in voltage.
Locked voltage - Trixx
I tried locking the voltage to avoid these jumps during load. This works, but it has the downside that the voltage does not go down when the GPU is idle. At the default load voltage of 1.087 V the difference vs default idle 0.806 V is about 35 W, and if I increase the voltage further this meaningless waste of energy will just grow. Hence I think locked voltage is a no go.
MSI Afterburner
Changing core voltage in MSI Afterburner has no effect whatsoever unless I force constant voltage, which of course I do not want to do.
I know this must be possible, but the strange interplay between VDCC and Power limit messes it up for me.
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