[Reddit] RX 480 fails PCI-E specification - Page 59 - Overclock.net - An Overclocking Community

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[Reddit] RX 480 fails PCI-E specification

 
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post #581 of 1129 (permalink) Old 07-02-2016, 08:46 AM
 
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r9 280s do use more energy than the RX 480.
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post #582 of 1129 (permalink) Old 07-02-2016, 08:48 AM
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Originally Posted by Kpjoslee View Post

Nah, it is not about the node, just poorly designed ref card. When the market has enough of AIBs with 8 pins, they should just phase out reference versions. It is not worth all these controversies and dramas for $30-40 savings.

I wouldn't go so far as to say it is poorly designed. It has a vastly over-engineered and high quality VRM and overall construction - the power delivery circuitry on this board is higher quality than just about any other reference card ever made at any price point - including the likes of the GTX 980ti. It's a true six-phase 600A VRM to power a 110 W GPU...

The only issue is that there seems to be a configuration or isolation issue - a minor bug with potentially negative ramifications. The same power draw using the 6-pin power rather than the slot power would be a near total non-issue.

AMD said they can fix it with a driver update without hurting performance, which suggests that they can simply tell the VRM to pull power differently - or they can adjust their boot-time calibration feature (which is most likely at fault, IMHO, as it is one of the only new potentially invasive features regarding power delivery and VRM configuration).
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post #583 of 1129 (permalink) Old 07-02-2016, 09:02 AM
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Originally Posted by mutantmagnet View Post

I'll assume you wrote the last part incorrectly.

If PCISig aren't concerned in terms of how this impacts their certification that's fine and reduces the problems AMD could deal with but going over the physical limits isn't something that should be ignored. Those amperage maximums mean that the 480 increases the risk of shorting them out over anything else put in that slot.

 

Yeah, there's a mistake there that I didn't catch.

 

That's written correctly for an overclocked scenario, which I forgot to add. PCI-SIG's CEM v3.0 spec basically states that cards conforming to their specification and compliance testing can draw a maximum of 75W over the +12v PCI-E rails if the card draws anything up to 150W from auxiliary power. 

 

As long as the add-in board does not draw more than the stated maximums from the PCI-E slot, and so long as it also draws enough to meed the minimum requirements for the interconnectivity to work, they don't really care if the card draws over the limit when overclocked, or if you consume more than 150W from the auxiliary power when overclocked. It's concerning, but it's not their problem.

 

So long as it passes compliance testing at stock speeds, it gets the noddy badge. And if you look at PCPer's testing on the overdraw limits, at stock it doesn't go over the recommended limits, while it definitely overdraws when you make changes to either the clock speed, the voltage profiles, or the power limits. 

 

 

And in the cases where cards at stock are overdrawing, I think that's a per-sample or batch issue where individual cards are fed more voltage as a result of AMD's adaptive aging compensation. They're increasing clocks and voltages at stock to be able to give you a similar performance level when the card is 4-6 years old, and the driver defaults, coupled with the settings in the BIOS, cause the card to draw a little over 76W at stock. Those stock Witcher 3 benchmarks that display overdraw are probably with a card that has all of these problems mixed in to cause it to consume more power than is ideal.

 

 

I think the driver fix will be to make the power management that little bit more aggressive, as well as include resetting the default power limit to -20% with a 5% increase in clock speed to make up for the performance loss. A decrease in power consumption and an increase in performance is what everyone wants, and there's an optional solution where the card's firmware is altered to make it derive more power from an auxiliary source rather than the motherboard. 


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post #584 of 1129 (permalink) Old 07-02-2016, 09:05 AM
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Anyone who knows or an EE, tell us how the different +12v sources are connected to the VRMs.

Like how are they're balanced to ensure that too much power isn't taken over the PCIe bus. Is there a control circuit before the VRM to dial that in?

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post #585 of 1129 (permalink) Old 07-02-2016, 09:30 AM
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Quote:
Originally Posted by umeng2002 View Post

Anyone who knows or an EE, tell us how the different +12v sources are connected to the VRMs.

Like how are they're balanced to ensure that too much power isn't taken over the PCIe bus. Is there a control circuit before the VRM to dial that in?

For your reading:
http://www.geeks3d.com/20100504/tutorial-graphics-cards-voltage-regulator-modules-vrm-explained/2/


This may be helpful as well - it is by Sin0822. It is for motherboards, but the principles for GPUs are very similar.
http://sinhardware.com/index.php/vrm-articles/82-vrm-guide

See these as well:








Mahigan might be able to give you a hand here as well.


Quote:
Originally Posted by looncraz View Post

I wouldn't go so far as to say it is poorly designed. It has a vastly over-engineered and high quality VRM and overall construction - the power delivery circuitry on this board is higher quality than just about any other reference card ever made at any price point - including the likes of the GTX 980ti. It's a true six-phase 600A VRM to power a 110 W GPU...

The only issue is that there seems to be a configuration or isolation issue - a minor bug with potentially negative ramifications. The same power draw using the 6-pin power rather than the slot power would be a near total non-issue.

AMD said they can fix it with a driver update without hurting performance, which suggests that they can simply tell the VRM to pull power differently - or they can adjust their boot-time calibration feature (which is most likely at fault, IMHO, as it is one of the only new potentially invasive features regarding power delivery and VRM configuration).


This. It is kind of sad that Nvidia cheaps-out on the VRM of its reference board designs. Whatever their other flaws, AMD does do a bit of overkill on its power delivery, which I think is excellent.

It is scary that a $200 GPU has a better power delivery than a $700 one (look at the GTX 1080 Founder's). For that kind of $$$, I'd expect at least DirectFET mostfets and at least 6 phases.
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post #586 of 1129 (permalink) Old 07-02-2016, 10:19 AM
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Quote:
Originally Posted by CrazyElf View Post


For your reading:
http://www.geeks3d.com/20100504/tutorial-graphics-cards-voltage-regulator-modules-vrm-explained/2/


This may be helpful as well - it is by Sin0822. It is for motherboards, but the principles for GPUs are very similar.
http://sinhardware.com/index.php/vrm-articles/82-vrm-guide

See these as well:



Mahigan might be able to give you a hand here as well.
This. It is kind of sad that Nvidia cheaps-out on the VRM of its reference board designs. Whatever their other flaws, AMD does do a bit of overkill on its power delivery, which I think is excellent.

It is scary that a $200 GPU has a better power delivery than a $700 one (look at the GTX 1080 Founder's). For that kind of $$$, I'd expect at least DirectFET mostfets and at least 6 phases.

 

Agreed. It does suck that Nvidia skimps out on reference board designs compared to AMD. But if you look at it from a margins perspective, it makes sense for a business to do so. If you can create a design that delivers the specifications you had laid out. but with the minimum that you will need to reach those specifications, then you are increasing your margins on each product sold. AMD could very much not design such overkill and increase their margins. So from a business standpoint, I don't understand why they would go for overkill. But from a consumer standpoint, I do see your point.


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post #587 of 1129 (permalink) Old 07-02-2016, 10:36 AM
 
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Quote:
Originally Posted by CrazyElf View Post

For your reading:
http://www.geeks3d.com/20100504/tutorial-graphics-cards-voltage-regulator-modules-vrm-explained/2/


This may be helpful as well - it is by Sin0822. It is for motherboards, but the principles for GPUs are very similar.
http://sinhardware.com/index.php/vrm-articles/82-vrm-guide

See these as well:








Mahigan might be able to give you a hand here as well.
This. It is kind of sad that Nvidia cheaps-out on the VRM of its reference board designs. Whatever their other flaws, AMD does do a bit of overkill on its power delivery, which I think is excellent.

It is scary that a $200 GPU has a better power delivery than a $700 one (look at the GTX 1080 Founder's). For that kind of $$$, I'd expect at least DirectFET mostfets and at least 6 phases.
What good is a 600A power framework on a 110 watt gpu? Is it compensatorially built-in for temperature gradation losses/wear-and-tear over time?
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post #588 of 1129 (permalink) Old 07-02-2016, 10:59 AM - Thread Starter
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Originally Posted by CataclysmZA View Post

Yeah, there's a mistake there that I didn't catch.

That's written correctly for an overclocked scenario, which I forgot to add. PCI-SIG's CEM v3.0 spec basically states that cards conforming to their specification and compliance testing can draw a maximum of 75W over the +12v PCI-E rails if the card draws anything up to 150W from auxiliary power. 

As long as the add-in board does not draw more than the stated maximums from the PCI-E slot, and so long as it also draws enough to meed the minimum requirements for the interconnectivity to work, they don't really care if the card draws over the limit when overclocked, or if you consume more than 150W from the auxiliary power when overclocked. It's concerning, but it's not their problem.

So long as it passes compliance testing at stock speeds, it gets the noddy badge. And if you look at PCPer's testing on the overdraw limits, at stock it doesn't go over the recommended limits, while it definitely overdraws when you make changes to either the clock speed, the voltage profiles, or the power limits. 



Sorry, but you are close, but still wrong.

The specification is 66 watts of 12 volts over the PCIe slot and 75 watts TOTAL for the entire PCIe connector. You are forgetting that in addition to the 5 12 volt lines on the PCIe connector, which the pins are rated at a maximum of 1.1 amps each (for a total of 5.5 amps for 12v, or 66 watts) there is also 5 volts and 3.3 volts. You have to remember to could the total wattage of the other voltages as well, which can't go over 75 watts in total, but as far as 12 volts are concerned, it can only be 66 watts.

And as you can clearly see, in the Metro Last Light test they ran, which wasn't overclocked, the AMD RX 480 is CLEARLY over that 66 watt maximum.
Quote:
The PCI Express specification language is more specific on currents than wattage limits, calling for a maximum of 5.5A over the +12V line and 3A over the +3.3V. Our direct power measurement tools and hardware allow us to not just measure power but directly record the amperage and voltage.

This graph shows that result, running Metro: Last Light at 4K with the Radeon RX 480 at stock settings. The green line is the amperage being used by the +12V on the motherboard PCI Express connection and the blue represents the same over the 6-pin power connection. The motherboard is pulling more than 6.5A through the slot continuously during gaming and spikes over 7A a few times as well. That is a 27% delta in peak current draw from the PCI Express specification. The blue line for the 6-pin connection is just slightly lower.

https://www.pcper.com/reviews/Graphics-Cards/Power-Consumption-Concerns-Radeon-RX-480/Overclocking-Current-Testing


So, as you can see, no matter how you slice it, AT STOCK CLOCKS, the RX 480 exceeds PCI-SIG standards by 1 to 1.5 amps, thus failing specifications.

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post #589 of 1129 (permalink) Old 07-02-2016, 11:05 AM - Thread Starter
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Originally Posted by CataclysmZA View Post

... and there's an optional solution where the card's firmware is altered to make it derive more power from an auxiliary source rather than the motherboard. 

That's already been addressed in the PCPer video I linked to. You are assuming that they have circuitry built in that allows them to alter that flow via BIOS. To my knowledge, no other card has ever had such a thing, but I could be wrong. That seems like an expensive component to install for something that, if designed properly once, would never need to be changed. Instead of doing the 50/50 split that AMD has apparently done with the RX 480, they should have done a 40/60 split (40% power from the PCIe and 60% from the 6-pin PEG) and this issue never would have happened.

Again, if you look back on the video I linked, they talk about how NVIDIA/ASUS did this with the Strix 960. While it went over on the 6-pin PEG, it never went over 30 watts (of the 66 allowed) on the PCIe slot for 12V.

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post #590 of 1129 (permalink) Old 07-02-2016, 11:11 AM
 
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Originally Posted by ProclusLycaeus View Post

That's already been addressed in the PCPer video I linked to. You are assuming that they have circuitry built in that allows them to alter that flow via BIOS. To my knowledge, no other card has ever had such a thing, but I could be wrong. That seems like an expensive component to install for something that, if designed properly once, would never need to be changed. Instead of doing the 50/50 split that AMD has apparently done with the RX 480, they should have done a 40/60 split (40% power from the PCIe and 60% from the 6-pin PEG) and this issue never would have happened.

Again, if you look back on the video I linked, they talk about how NVIDIA/ASUS did this with the Strix 960. While it went over on the 6-pin PEG, it never went over 30 watts (of the 66 allowed) on the PCIe slot for 12V.

The GTX 960 and 950 pull more than the RX 480 pull from the PCIe Slot, this "issue" is ridiculous, especially when you factor in that the 950 have spikes of 200W while the RX 480 goes to 140W from the PCIe Slot alone, the thing is that due to average lower power consumption the 950 does have lower average PCIe Slow power consumption, but the 200W spikes are still there.
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