hbm2 voltage locked ?

[Soulkeeper]

Can anyone actually change this ? I'm seeing conflicting reports around the internet about HBM2 being locked at 1.35v for vega64 and 1.25v for vega56.
Other people are saying you change it using softmod or whatever program, and it don't really change.
It is linked to gpu vcore somehow ?

Has anyone done some testing to shed some light on this ?
I guess power usage and voltmeters would be the only real way to know ...

 

[Soulkeeper]

Here is some other information i've been gathering over the past week.
https://www.phoronix.com/forums/for...6634-vega-dota2-lockups?p=1047823#post1047823
apparently I have found a way to lower the hbm voltage Just not set it to what I want exactely.

 

[Shmee]

On my card I can change it in the radeon software fine using wattman. I am undervolting though. On windows 10

 

[Soulkeeper]

On my card I can change it in the radeon software fine using wattman. I am undervolting though. On windows 10

Are you sure it is actually changing it tho ?
does raising/lowering the voltage change the clock speeds you're able to hold stable ?

 

[Shmee]

I have not done a whole lot of testing, but I am pretty sure the minimum readings for the VDDC are effected when changing the HBM voltage. Note that the VDDC will not go lower than the set HBM voltage, read more here I found an interesting post about it, not sure if this is an updated guide though.

https://forums.overclockers.co.uk/threads/vega-64-hbm-overclock-suggestion.18799701/

Anyway I will do more testing and fiddling, but I believe I am at 1050 mV now with 1025 MHz memclk.

 

[CuriousShawn]

I tried to change the memory voltage of my Vega 56 reference card to 1.35V by using registry hack on Windows, but sensor readings on HWInfo64 said that it remained at 1.2V. But flashing with vega64 bios changed the voltage to 1.35V.

 

[thilanliyan]

I didn't think changing memory voltage was possible on Vega.

 

[Shmee]

Might depend on card and BIOS. At least in the latest drivers, it gives me the option in wattman.

 

[CuriousShawn]

For those people who use Windows, I'd like to suggest to use HWInfo64 instead of GPU-z for this subject.
It's because HWInfo64 gives you HBM2 voltage readings which GPU-z doesn't give you. You'll find that the HBM2 voltage is locked all the time.

The memory voltage field in Radeon WattMan for Vega cards is not the voltage applied to HBM2 stacks, it's the threshold voltage to enter maximum memory state.
You can confirm this by following the steps described below:

1. Run HWInfo64 and start monitoring
2. Open Radeon WattMan
3. Reset WattMan settings and then switch to custom profile
4. Set the voltage control to manual mode
5. Set the GPU frequency by right clicking vertical lines below STATE 1 - 7 On GPU states panel on the WattMan, and then click "set as minimum state", and finally, click "apply"
- Confirm VDDC and MVDDC while doing this step, you'll confirm that MVDDC(=HBM2 voltage) is locked all the time, while VDDC(=GPU voltage) changes with regard to the GPU states
- You'll also confirm that GPU Memory Clock and SoC Clock changes according to the GPU state you set as the minimal state, and that Memory frequency reaches its maximum state when the GPU core voltage reaches the memory voltage value which you can edit in the WattMan
6. Change the memory voltage for memory state 3, say, from 950mV to 1000mV (or to whatever higher than the default value)
7. Repeat Step 5
- You'll confirm that the VDDC value which GPU Memory Clock reaches its maximum state has changed to match with your input

8. Set the minimum state of GPU as state 0
9. Change the voltage for maximum memory state to higer than the voltage for GPU state 7
10. Set the memory state 3 as the minimum state
- You'll confirm that VDDC changed to the max memory state voltage, while GPU core clock stays at idle clock

I believe that this is why the memory voltage you can change in the WattMan is considered as a floor voltage of the GPU, for the VDDC will not go lower than the memory voltage you put in the WattMan, even if the voltage required for the GPU core is way lower than the applied voltage.

 

[Shmee]

Thanks for the detailed explanation. I remember that I saw some similar post now on overclockers.uk I believe, where they were talking about undervolting and HBM ocs.

For the sapphire card I have, what would you recommend for a HBM voltage setting, if trying to undervolt and OC the HBM? I usually get boost clock of around 1600-1630 on the core.

 

[CuriousShawn]

For the sapphire card I have, what would you recommend for a HBM voltage setting, if trying to undervolt and OC the HBM? I usually get boost clock of around 1600-1630 on the core.

I haven't spend time with Nitro Vega 64, so I'll give you the way I overclock HBM2 based on my experience with Vega 64 LC and Vega 56 ref cards.
The basic principle would look like below:
[ target memory voltage = minimum voltage required to keep your target memory clock + max Vdroop amount ]

Let's confirm the max Vdroop amount first:

- Undervolt GPU without overclocking HBM2 (your current GPU setting should be good enough)
- Set voltage mode as manual mode
- Set GPU state 7 as the minimum state
- Run 3DMark Firstrike Ultra GT1 while monitoring the VDDC of your card(of course you need a time-voltage graph or log file). On my Vega 56 ref card, it's about 50mV.​

And you can find your memory voltage by following steps below:

- Set your target memory frequency
- Set voltage to auto mode
- Set memory state 3 as the min memory state
- Confirm VDDC value by using HWInfo64 or GPU-z
​

The VDDC value + Vdroop amount acquired by the steps above would be your target memory voltage.

​