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[Reddit] RX 480 fails PCI-E specification

 
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post #201 of 1129 (permalink) Old 06-30-2016, 09:14 AM
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Quote:
Originally Posted by tpi2007 View Post

I was just looking for that. Here it is:
All in all the issue here is that while the R9 295X2 didn't exceed the PCIe slot spec and when it came to the 8-pin connectors it made clear what its requirements were, at the end of the day it wasn't a PCIe compliant device and therefore not included on the Systems Integrator List because of this, so people knew what they were getting into.

The RX 480 is a mainstream card that is likely to go into many OEM systems, the implications are completely different.

I'd like to ask the people who are trying to downplay the issue if they'd be fine if a GTX 750 Ti without a power connector would pull 90w from the slot instead of its rated 60w. All of that talk about the card being great to upgrade crappy OEM systems with an otherwise decent Intel CPU but only integrated graphics would go down the drain. Nobody would recommend people risk damaging the system with an out of spec card. The 750 Ti is such a great card because it does what it says.

And again, the reference GTX 970 comes with two six pin power connectors and has a 145w max board power. The RX 480 has a 150w rating and only has one. AMD was even boasting about it (see below). Considering the measurements made by the majority of sites, not even counting the ones that specifically measured the PCIe slot demands, it seems pretty clear that the card uses more than 150w very frequently. It's inadequate and misleading to think it's a 150w card.
Warning: Spoiler! (Click to show)

I get what you're saying, I really do, and I don't disagree. However what really ruffles my feathers is certain people have their pitchforks ready 24/7 and seem all too happy to crucify AMD at the first hint of trouble.

I mean, look at the responses when it was pointed out a certain Asus 960 card had the same issue. Nothing but excuses on why it's not important, how it isn't nVidia's fault (even though nVidia had to approve the board design), how people in the red camp are just deflecting and it changes nothing etc. Then again, this is the OCN news section so I should've expected as much. doh.gif

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post #202 of 1129 (permalink) Old 06-30-2016, 09:14 AM
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Originally Posted by lolfail9001 View Post

OEM PSUs will LOVE that juicy over 150W power consumption under load.

OEM power supplies are not bad lol.

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post #203 of 1129 (permalink) Old 06-30-2016, 09:14 AM
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Originally Posted by Themisseble View Post

Yeah well AMD does make good and efficient cards... why does RX 480 use so much power?

 

Hasn't this always been an issue since Hawaii? It uses more power than expected, because AMD's trying to do more things with a denser design. I'm not sure why AMD didn't just slap an 8-pin connector on there for funsies.

 

Also, taken from this table in the PCI-E Electromechanical Specification version 3.0...

 

If we apply the maximum allowed voltages for a 75W slot, we get 10.7W + 71W = 81W. That does seem to correlate with the reported power draws.

 

3.3Vaux is an optional addition, most manufacturers don't include it in because it looks like it's only adding an additional 1W of power.

 

With a 150W card reporting itself correctly to the board, the 12v rail supplies a maximum of 78.75W, but that rarely is ever the case. 

 

None of this seems straightforward.


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post #204 of 1129 (permalink) Old 06-30-2016, 09:26 AM
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Oh no, 750ti! (FYI this is all through the PCIE bus)



I know I overclocked the snot out of mine and had them folding for months with no issues. Go home and find something better to do people.

Source

480 for comparison.




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post #205 of 1129 (permalink) Old 06-30-2016, 09:30 AM
 
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Quote:
Originally Posted by Klocek001 View Post

what exactly is the point of this?

Maybe EVGA knew of the 480 release? smile.gif
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post #206 of 1129 (permalink) Old 06-30-2016, 09:35 AM
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Originally Posted by prznar1 View Post

I will say it again. PCi-e SIG had rx 480 in their own hands, and they aproved it. No need to worry about it to much.

 

It could have been verified when AMD had a lower-clocked, or even referenced clock-ed card tested. PCI-SIG testing, AFAIK, doesn't cover overclocking requirements.

Quote:
Originally Posted by DaaQ View Post

Ok, since the bandwagon is speeding along so fast that pitchforks are flying everywhere. I have wasted 45 minutes to read through this thread. I am going to provide some information I am pretty sure few will actually read. I will start by getting the stuff I am not going to bother providing any backup for first.

According to the internet, the PCIE slot pulling over 75w was from 2 reviewers out of 20, of the other reviewers who were shared this information, non were able to recreate the scenario. So not being able to recreate the current overdraw by other reviewers, really means something in itself. But AMD fail is AMD fail, such is the oh too familiar mantra. rolleyes.gif Anyone that comes at me with proof.gif or your argument is invalid. How about you actually do some reading if your so concerned with proof. I seen the above information earlier in the day and am not going to spend the time trying to convince people that won't be convinced anyway.

 

Don't you really mean to say that few reviewers were able to measure PCI-E power draw? Not everyone has that kind of equipment on hand.

 

As for the information from that document, it's over 800 pages long. There's so much information available that finding anything that actually tells us what's going on here is going to take a very, very long time. It might be better to ignore those numbers and work off the PCI-E Electromechanical specification.

 

http://download.csdn.net/detail/jianjunzaixian/9229521

 

I've pasted the relevant pages for everyone to read.

 

 

 

 

As you can see, at no point is the PCI-E slot ever officially given more than 75W of power to work with. Both the board and GPU need to adhere to that spec while making use of aux inputs to make up the difference. 

 

Quote:
Originally Posted by nagle3092 View Post

Oh no, 750ti! (FYI this is all through the PCIE bus)

I know I overclocked the snot out of mine and had them folding for months with no issues. Go home and find something better to do people.

Source

480 for comparison.
 

The average draw of the GTX 750 Ti was below 75W, which is expected. The average of the RX 480, as measured in that graph, is 80W. That should not be the case, and the RX 480 is overdrawing on the PCI-E specification most of the time.

 

I mean, sure, there's provision for drawing 81W, at a stretch, if you're abusing the tolerances as much as you can and guessing that the board can handle it and doesn't have cheap caps, which is what AMD is doing here. I can see why they're doing it this way, but it's not the most ideal way to go about this. Slapping on an 8-pin connector would have rendered this all a non-issue.

 

Also, both graphs are squashed in, so aside from displaying the average range, they're not very useful. Using those to prove your point could be interpreted as intending to mislead people.


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post #207 of 1129 (permalink) Old 06-30-2016, 09:38 AM
 
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Quote:
Originally Posted by nagle3092 View Post

Warning: Spoiler! (Click to show)
Oh no, 750ti! (FYI this is all through the PCIE bus)



I know I overclocked the snot out of mine and had them folding for months with no issues. Go home and find something better to do people.

Source

480 for comparison.

Apply baking soda to burned area.
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post #208 of 1129 (permalink) Old 06-30-2016, 09:38 AM
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Originally Posted by andydabeast View Post

Because then how would the bracket connect into a traditional case?
Make a PCI extension bracket to compensate for the added depth. All I'm asking is if something like this could be used to skirt or bypass PCI-E regulations ?

The allowance of higher-than-spec power usage through the PCI-E could set a precedent for the future. If it doesn't fry the motherboard then maybe the spec is too conservative to begin with.
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post #209 of 1129 (permalink) Old 06-30-2016, 09:56 AM
 
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I already bought Nvidia, I hope AMD can get their act together with VEGA so I can get back to a product that I feel is not milking me alive.
.

I'm sad to see they're screwing so much, first their horrible efficiency with Polaris, with roughly the same efficiency of a GTX 970, a card that was built on 28nm, then Overhead issues still being present and now this.

I've said before that AMD efficiency numbers are based on the RX 460/470 and that Polaris seem to be an architecture made for the low end, Polars RX 480 being so inefficient is just a side effect of AMD stretching this architecture into performance segments it wasn't really intended to be in, just like Raja said in that PCPer interview "Polaris 11 was our main focus".

Sad that Samsung haven't bought AMD yet, I shouldn't have to pay almost 500$ for a 1070, a GPU with such small die that even a 960 would be considerably more expensive to fabricate.
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post #210 of 1129 (permalink) Old 06-30-2016, 10:09 AM
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Quote:
Originally Posted by CataclysmZA View Post


Don't you really mean to say that few reviewers were able to measure PCI-E power draw? Not everyone has that kind of equipment on hand.

As for the information from that document, it's over 800 pages long. There's so much information available that finding anything that actually tells us what's going on here is going to take a very, very long time. It might be better to ignore those numbers and work off the PCI-E Electromechanical specification.

http://download.csdn.net/detail/jianjunzaixian/9229521

I've pasted the relevant pages for everyone to read.










As you can see, at no point is the PCI-E slot ever officially given more than 75W of power to work with. Both the board and GPU need to adhere to that spec while making use of aux inputs to make up the difference. 

The average draw of the GTX 750 Ti was below 75W, which is expected. The average of the RX 480, as measured in that graph, is 80W. That should not be the case, and the RX 480 is overdrawing on the PCI-E specification most of the time.

I mean, sure, there's provision for drawing 81W, at a stretch, if you're abusing the tolerances as much as you can and guessing that the board can handle it and doesn't have cheap caps, which is what AMD is doing here. I can see why they're doing it this way, but it's not the most ideal way to go about this. Slapping on an 8-pin connector would have rendered this all a non-issue.

"it's over 800 pages long"
"There's so much information available that finding anything that actually tells us what's going on here is going to take a very, very long time."

Well, only chapter 5 (power management) and 6.8 to 6.16 (power budgeting capabilities) are about power which is about 77 pages.

Plus someone has already done the digging ( see his post below)


A few quotes from the manual,

"PCI Express provides a mechanism for software controlled limiting of the maximum power per slot
that a PCI Express adapter (associated with that slot) can consume."

" Scenario 3: An Adapter Consuming 30 W
If the adapter is plugged into a form factor #1 40 W slot, the Slot Power Limit control
mechanism is followed, and the device operates normally.

If the adapter is plugged into a form factor #1 25 W slot, the Slot Power Limit control
mechanism is followed, and the device must scale down to 25 W or disable operation.

If the adapter is plugged into a form factor #2 15 W slot, the Slot Power Limit control
mechanism is followed, and the adapter must scale down to 15 W or disable operation. An
adapter that does not scale within any of the power limits for a given form factor will always be
disabled in that form factor and should not be used. "

I dont know how the motherboard 'disables' the adapter/video card in this scenario, I assume the motherboard disables it by cutting power if it doesn't want to scale down but I haven't read it completely though.

spoiler (Click to show)
Quote:
Originally Posted by DaaQ View Post

Ok, since the bandwagon is speeding along so fast that pitchforks are flying everywhere. I have wasted 45 minutes to read through this thread. I am going to provide some information I am pretty sure few will actually read. I will start by getting the stuff I am not going to bother providing any backup for first.

According to the internet, the PCIE slot pulling over 75w was from 2 reviewers out of 20, of the other reviewers who were shared this information, non were able to recreate the scenario. So not being able to recreate the current overdraw by other reviewers, really means something in itself. But AMD fail is AMD fail, such is the oh too familiar mantra. rolleyes.gif Anyone that comes at me with proof.gif or your argument is invalid. How about you actually do some reading if your so concerned with proof. I seen the above information earlier in the day and am not going to spend the time trying to convince people that won't be convinced anyway.

Now for the good stuff.

Here's a juicy bit from this link here, which ironically is where I heard some of the above. https://www.reddit.com/r/pcmasterrace/comments/4qfy9d/i_work_at_amd_the_time_has_come_to_ama_about/
Quote:
Ektobuffer 3 points 3 hours ago
Maybe i can helb you out a bit Raja.
I have just read the PCI-E 3 specifications and they are telling me something different. In my understanding the 75 watt isnt the maximum limit, its just the default value on startup of the motherboard. The motherboard it self sets the maximum allowed watt per slot in the "Slot Capabilities Register" which you can configure up to over 300 watt per slot. In the bits 7 to 14 "Slot Power Limit Value" you can set 250, 275, 300 and above 300 watt. This will be multiplied with bits 15 to 16 "Slot Power Limit Scale" in steps x1 ,x0.1, x0.01 and x0.001. So its up to the motherboard manufacturer and the power management on it how many watt the slot is capable of.
The Specifications do define the protocol and not the hardware specs of the PCI-E slot. If a manufacturer uses better parts which can handle higher amps on the contacts and the lines, they can allow the devie in the slot a higher power consumption than 75 watt via these registers.
Sadly most people doesnt even read the specifications and judge things they dont understand.
http://composter.com.ua/documents/PCI_Express_Base_Specification_Revision_3.0.pdf

Now the link provided in that quote is really interesting. ( DL it Looniam if you don't have it you will love it )
Hopefully those that are so inclined actually spend some of their time and actually read some of the info in that link.

So it's late and I need to get to bed, but this is what I quickly found in that 800+ page document.
Quote:
Power limits on the platform are typically controlled by the software (for example, platform
firmware) that comprehends the specifics of the platform such as:
15 Partitioning of the platform, including slots for I/O expansion using adapters
Power delivery capabilities
Thermal capabilities
This software is responsible for correctly programming the Slot Power Limit Value and Scale fields
of the Slot Capabilities registers of the Downstream Ports connected to slots. After the value has
20 been written into the register within the Downstream Port, it is conveyed to the adapter using the
Set_Slot_Power_Limit Message (see Section 2.2.8.5). The recipient of the Message must use the
value in the Message data payload to limit usage of the power for the entire adapter, unless the
adapter will never exceed the lowest value specified in the corresponding form factor specification.
It is required that device driver software associated with the adapter be able (by reading the values of
25 the Captured Slot Power Limit Value and Scale fields of the Device Capabilities register) to
configure hardware of the adapter to guarantee that the adapter will not exceed the imposed limit.
In the case where the platform imposes a limit that is below the minimum needed for adequate
operation, the device driver will be able to communicate this discrepancy to higher level
configuration software. Configuration software is required to set the Slot Power Limit to one of the
30 maximum values specified for the corresponding form factor based on the capability of the
platform.
The following rules cover the Slot Power Limit control mechanism:
For Adapters:
Until and unless a Set_Slot_Power_Limit Message is received indicating a Slot Power Limit
35 value greater than the lowest value specified in the form factor specification for the adapter's
form factor, the adapter must not consume more than the lowest value specified.
PCI EXPRESS BASE SPECIFICATION, REV. 3.0
528
An adapter must never consume more power than what was specified in the most recently
received Set_Slot_Power_Limit Message or the minimum value specified in the corresponding
form factor specification, whichever is higher.

Page 527 to be specific, this concerns slot power limit control.
The above sounds to me either, vBIOS or BIOS level. Would be quite interesting if the motherboard was responsible for assigning the slot power limit wouldn't it?

devil.gif away.
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