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AMD Kaveri Refresh A10-7870K Apu arrives. - Page 48

post #471 of 532
Quote:
Originally Posted by The Stilt View Post

All Kaveri / Godavari parts are able to run at 2400MHz MEMCLK as long as the settings are correct.
It should require no additional VDDNB voltage either, unless your chip is running extremely hot. To ensure stability in all conditions I would recommend using the default voltage together with 80% or 60% load-line adjustment.

On boards which feature an advanced VRM controller (IR356x) it is important NOT to use the fixed voltage mode.
This is because the output voltage feeds two different domains, with two different voltage level requirements; CNB has default voltage < 1.1250V while the GNB always defaults to 1.225V (KV) or 1.275V (GV) in 3D. If you enable the fixed voltage mode and set it to eg. 1.150V you will most likely have no issues on desktop, but in 3D the GPU might potentially crash due undervoltage. Likewise if you set the fixed voltage to e.g. 1.2750V, you will just end up wasting power on the desktop when the GPU is not used. When the fixed voltage option is used the VID commands issued by any of the domains (CPU, CNB, GNB) are completely ignored. As the name indicates, the voltages are fully fixed.

When using unofficially supported MEMCLK (i.e. 2400MHz) most ODMs automatically add a voltage offset to the VDDNB voltage. In most cases the automatic voltage offset is way too large and it only results in excessively high power consumption with no additional stability. In fact in some cases the automatic voltage offset is so high that the resulting output voltage violates AMD´s electrical specifications, and potentially can cause instability or even degradation. To ensure there is no excessively high automatic voltage offset added by the bios, you must ensure that the offset voltage is NOT set to Auto. If you are adjusting either CPU, NCLK, GPU or MEMCLK frequencies above their default level you should use at least 0.00625V offset voltage (±, doesn´t matter). Setting the offset value to anything other than Auto will prevent the bios from using the automatic voltage offsets.

Overclocking the APUs has always been extremely tricky since adjustments made to one domain also affect the other.

Kaveri / Godavari will not be able reach MEMCLKs higher than 2400MHz, and the reason for this limitation is rather simple.
During the boot the memory controllers perform a calibration process dubbed as training. The training process will adjust the settings until the signal patterns match the predefined pattern for the set memory frequency. The memory controllers perform training at several different frequencies depending on the desired memory clocks. For example when the desired MEMCLK is 2133MHz the memory training will be performed at 800, 1066, 1333, 1600, 1866 and 2133MHz frequencies. The memory signals can drift from their trained settings only so slightly without causing any problems. If the actual signaling changes to either direction, at some point it will either result in memory errors or system crash depending on how much apart the signaling is and how many errors are produced because of it.
This is the reason why using 110MHz BCLK with 3:28 (1866MHz) MEMCLK ratio (= 2053MHz) might be unstable while the 3:32 (2133MHz) MEMCLK ratio at 100MHz BCLK works just fine.

The memory controller in Kaveri / Godavari cannot train the memory for any frequency higher than 2400MHz.
You can try to reach higher frequencies by increasing the BCLK frequency from 100MHz, however in that case you are playing with the signal margins which is never advised for the sake of stability.
Regardless how much you increase the BCLK above the default 100MHz value, the memory will not be trained for any other frequency but 2400MHz. That´s why anything higher than 2400MHz will not be reliable or stable, no matter how much you fool around with the voltages or timings.

These limitations will apply regardless of the motherboard as the limitation is purely in the memory controller.
Some motherboards might have slightly shorter trace lengths, larger trace spacing or cleaner supply for VDDIO or the reference voltages, but the difference between the designs will still be non-existent due the limitations set by the memory controller itself.

To maximize the memory performance and stability on Kaveri / Godavari, use following configuration:

- Two DRAM modules
- Dual rank modules (two sided with 8 ICs on each side)
- Hynix CFR (2Gb), MFR (4Gb) or Samsung D-Die (2Gb) or Q-Die (4Gb)
- Micron / Elpida and Nanya ICs are usually good for 1600-1866MHz on AMD

The penalty from using single rank modules is worth around one speed class or 133MHz (2400MHz SR = 2133MHz DR, 2133MHz SR = 1866MHz DR).

On average (depending on leakage) the GPU reaches it´s maximal frequency with 1.27 - 1.30V actual.
In most cases the GPU and NCLK frequency scaling starts to show retardation if the voltage is raised beyond that.
The CNB/GNB voltage scaling is rather poor in Kaveri / Godavari, so trying to reach frequencies beyond the linear scaling curve by using excessively high voltage is futile and after a certain point dangerous to the silicon. Unless the iGPU is (for some odd reason) used for computing, overclocking the iGPU is rather pointless as at 2400MHz MEMCLK there is not enough of bandwidth to keep the GPU fully fed even at 600MHz.

The breakdown (absolute maximum) voltage for Kaveri / Godavari CNB/GNB (VDD_NB) is 1.320V
.

This was his post on the matter I raised smile.gif
post #472 of 532
Is there any way to force a certain voltage on the NB when the GPU is under load? I disabled every power management option on my mainboard, but no matter what I set from BIOS, as soon as the CPU has some load, it raises to 1.2125v, and whenever GPU has load, it goes to 1.2825.

I wonder how the Stilt managed to stress test the GPU at a lower voltage under load. Is it an issue (rather, a feature) of my motherboard or everyone is experiencing a similar behaviour?
post #473 of 532
You need to edit the GPU PowerPlay table in order to control the GPU voltage in different states (2D / 3D). No public software supports that, as far as I know. If you want to lower the UNB (CNB + GNB) voltage while the GPU is in 3D state, you need to use negative offset (bios control).
post #474 of 532
Quote:
Originally Posted by The Stilt View Post

You need to edit the GPU PowerPlay table in order to control the GPU voltage in different states (2D / 3D). No public software supports that, as far as I know. If you want to lower the UNB (CNB + GNB) voltage while the GPU is in 3D state, you need to use negative offset (bios control).

I will try to downclock the GPU from BIOS to check if the voltage gets still pushed to 1.28v under load. I will also try to force the same vNB voltage for all pstates with MSR Tweaker.

Other than that, I only have two options on my BIOS for offset:

1) CPU Voltage Offset with two options: OFF and +10%. I have enabled that in order to have more realistic measurement of applied voltage (with that option off, the effective voltage would be much lower than VID, now it's a bit higher but more accurate)

2) APU Load-line Calibration, with two options: Auto and 1/2 vcore. According to manual: APU Load-line Calibration helps prevent APU voltage droop when the system is under heavy load. I have no idea what's that 1/2 vcore option going to do though.

Not sure why I have these two options that seem to do the same thing. Which one of the two would you recommend to use?
post #475 of 532
The CPU Voltage options doesn't affect the VDDNB voltage, only VDDCR. ASRock FM2A88X-ITX+ uses a cheap VRM controller and most likely there is only a single load-line adjustment available (affects both loop, VDDCR and VDDNB). Their VDDNB option in bios probably just alters the CNB VID. If that's the case then it will have no effect on GPU 3D voltages. Despite it is the same voltage, the higher voltage requested by GNB during 3D will be driven instead of the CNB VID.

If the GPU is in 2D state and the voltage specified by the display driver (PowerPlay) is lower than VDDNB (CNB VID), then the voltage is what CNB VID specifies. Otherwise the voltage is ALWAYS defined by the PowerPlay tables of display driver. So no matter what you change in the bios, you won´t be able to lower the GPU voltage in 3D state.
post #476 of 532
Quote:
Originally Posted by The Stilt View Post

The CPU Voltage options doesn't affect the VDDNB voltage, only VDDCR. ASRock FM2A88X-ITX+ uses a cheap VRM controller and most likely there is only a single load-line adjustment available (affects both loop, VDDCR and VDDNB). Their VDDNB option in bios probably just alters the CNB VID. If that's the case then it will have no effect on GPU 3D voltages. Despite it is the same voltage, the higher voltage requested by GNB during 3D will be driven instead of the CNB VID.

If the GPU is in 2D state and the voltage specified by the display driver (PowerPlay) is lower than VDDNB (CNB VID), then the voltage is what CNB VID specifies. Otherwise the voltage is ALWAYS defined by the PowerPlay tables of display driver. So no matter what you change in the bios, you won´t be able to lower the GPU voltage in 3D state.

That is EXACTLY what I have been experiencing on my motherboard. If I set the VDDNB to a lower voltage than 1.125v, my setting is ignored and 1.125v is applied on idle. Whenever the CPU gets some load (Overdrive stress test), the NB is fed with 1.225v. Whenever the GPU has load (BOINC), it jumps to 1.28v.

However, if I set VDDNB at 1.3v from BIOS, it doesn't downvolt to the specified value in Powerplay.

I will try to downclock the GPU and report if it actually forces a lower voltage under 3D. That's the reason why I wanted to get a 7860K instead than the 7870K, because I feel that the downclocked GPU on the 7860K can get away with a much lower voltage. Unfortunately that CPU is nowhere to be found in my country, and in Europe in general.

However, what is in your opinion the difference between those two options? Does the APU Load line calibration affect all 3 voltages instead than only the vcore?
Edited by Feimitsu - 3/1/16 at 9:01am
post #477 of 532
The VRM controller only controls VDDCR and VDDNB. The power management always drives the highest voltage defined by any domain. If you set the CNB (CPU Northbridge) VID to 1.3V from bios, then it never drops below that level. Thats because the voltage domain is shared.

CNB Voltage = GNB Voltage == UNB Voltage.

The voltage levels can be specified separately for CNB and GNB and the higher voltage is always dominant, regardless which one it is. CNB voltage can be adjusted in bios, while GNB voltage request cannot be controlled by any public tool.
post #478 of 532
Thread Starter 
Quote:
Originally Posted by Feimitsu View Post


That is EXACTLY what I have been experiencing on my motherboard. If I set the VDDNB to a lower voltage than 1.125v, my setting is ignored and 1.125v is applied on idle. Whenever the CPU gets some load (Overdrive stress test), the NB is fed with 1.225v. Whenever the GPU has load (BOINC), it jumps to 1.28v.

However, if I set VDDNB at 1.3v from BIOS, it doesn't downvolt to the specified value in Powerplay.

I will try to downclock the GPU and report if it actually forces a lower voltage under 3D. That's the reason why I wanted to get a 7860K instead than the 7870K, because I feel that the downclocked GPU on the 7860K can get away with a much lower voltage. Unfortunately that CPU is nowhere to be found in my country, and in Europe in general.

However, what is in your opinion the difference between those two options? Does the APU Load line calibration affect all 3 voltages instead than only the vcore?

 

Now available here in the UK - though the price may be a little higher than it will be later.

post #479 of 532
Quote:
Originally Posted by Himo5 View Post

Now available here in the UK - though the price may be a little higher than it will be later.

I confirm they have it in stock, bought mine monday, got it yesterday (From UK to France).
post #480 of 532
Quote:
Originally Posted by Cherryblue View Post

I confirm they have it in stock, bought mine monday, got it yesterday (From UK to France).

Could you please check with AMD Overdrive what is the NB voltage under 3D load? I am thinking to switch from 7870K to 7860K if that voltage is much lower. tongue.gif
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