Review Radeon RX 480 – analysis of energy consumption and performance with new driver and option Compatibility Mode

Review Radeon RX 480 - analysis of energy consumption and performance with new driver and option Compatibility Mode

The problem of increased power consumption Radeon RX 480 through a PCI Express slot should come to a logical decision after the drivers Radeon Software 16.7.1. AMD has published the appropriate driver last night, we together with our colleagues today analyzed the energy card. We conducted performance tests, which showed little change due to the changed power distribution Radeon RX 480.

But first let me talk about the problem. AMD Radeon RX points for 480 typical power consumption of 150 watts. GPU itself consumes up to 110 watts, according to the PCB AMD specifications.

Seven phases supply power to the GPU and other components of the card. Of these six phases are allocated on the GPU. Of course, according to the phases to be fed power responsible for this PCI Express slot and an additional 6-pin power connector. Four of the seven phases are supplied from the additional connector, three – of PCI Express slot, and this is precisely the problem lies. Maximum power for the slot, and the additional connector is 75 Watts. But other factors should be taken into account here. For example, through a PCI Express slot runs more than one line voltage, power 75 watts is common. And in the case of Radeon RX 480 problem lies not only with abuse of power, but also in other nuances, which we will discuss below.

PCI SIG consortium, responsible for the standardization of PCI Express, specifies the maximum current to voltage lines 3.3 V and 12 V. In particular, for 12 zavyalen maximum current of 5.5 A. The measurements of test laboratories Tom’s Hardware and other publications revealed the passage of a number of cases higher currents. Namely, to 6.74 A, which corresponds to the excess of 22.5%. Such an overload can not be called serious, it is unlikely to lead to the loss of stability and damage to other components of the system, but still not very good, when the card does not fit the accepted standards.

Typical power consumption and practices

As we pointed out in our test, AMD Radeon RX 480 for the indicated typical power consumption of 150 W, and the power supply to the graphics card just limited to this level. PCI Express slot and a 6-pin socket provides up to 75 watts of power, if you do not take into account the different stresses line. AMD’s, probably felt that in view of 110 W to 150 W of available GPU graphics card is more than enough, but in fact it is not. Energy consume memory subsystem, graphics add-ons, you should also take into account the losses on the transformation of stress. Our colleagues have measured, in which Radeon RX 480 has consumed more than the stated 150 watts, so the video card is clearly not hurt to 8-pin auxiliary power. But such a move would have limited the number of potential buyers of AMD graphics cards, as in older systems 6-pin power connectors are more common 8-pin.

Of course, the 6-pin connector and can withstand more than 75 watts of power. Many readers probably the question arises, how is this possible if the connector is claimed 75 watts? But the different specifications directly to the electrical connector and PCI Express standard. Yet the PCI Express standard is different from the specifications of the connector development. Here are the details:

The danger lies in the overload sockets always current resistance contacts. When current passes through the slot, because of the contact resistance is observed voltage drop as a result of which heat is released. Typically, the contact resistance at these connectors is 1-10 milliohms. We will take for the calculations average 5 milliohms. Assume that the power of 170 Watts is split equally between the two supply inputs for line 12 it means current of 7.1 A. This current is 7.1 A, in turn, is divided between two positive conductors 6-pin connector. Therefore, each conductor current is about 3.5 A. As a result, the contact resistance of 5 milliohms it passes in heat capacity of the order of 175 mW. This heat is dissipated into the atmosphere and does not pass on the insulation, it usually goes through the conductor. It should also be borne in mind that partial power loss occurs at the two contacts “earth” 6-pin connector, so the situation is far from critical.

If you look at Molex connector specification is considered to be a valid current up to 9 A per conductor. Such connectors are often used in the same modular power supplies. Recall that in the case of graphics cards AMD Radeon R9 295X2 current per contact is also reached about 3.5 A, and the physical specifications of the contact stock remains decent.

AMD’s approach

With driver Radeon Software 16.7.1 AMD is offering a new option: Compatibility Mode. By default it is turned off, everything remains the same. But if a user turn on Compatibility Mode, the video card will work within specifications.

Review Radeon RX 480 - analysis of energy consumption and performance with new driver and option Compatibility Mode

But what did AMD, to reduce power consumption through a PCI Express slot? A driver interface or I2C PWM controller load distribution has been changed between the voltage phases. In particular, three phases, in which power is supplied to the PCI Express slot, part of the load were transferred to the three remaining phases, the power to which is supplied through additional PCI Express connector.

However, such a move was not without additional victims. Power GPU with the new driver and off mode Compatibility Mode still is about 110 watts, but after activation Compatibility Mode power consumption is reduced by about 7 watts. This step was made possible by reducing the clock frequency. So that the reduction of energy consumption is accompanied by a decrease in GPU clock frequencies.

Immediately, we note that the first and the last few seconds, you can safely ignore. But we still have added these areas to be able to easily analyze data. Now, let us explain what we tested. First, we performed heating the video card Radeon RX 480, and then proceeds to the test. We ran the game Rise of the Tomb Raider in resolution 1.920 x 1.080 pixels 2xSSAA, fixing the clock frequency.

Please compare the clock speeds Radeon RX 480 with different versions of the driver and the mode. It should be noted that the new driver (orange line) clock speeds are slightly higher frequency of 1.266 MHz, lasts longer than the driver Radeon Software 16.6.2 (blue graph). In the case of Radeon Software 16.7.1 with active Compatibility Mode (green graph) video frequency is much lower.

Average clock GPU frequency was 1,218 MHz previously, now with standard settings, it increased to 1.222 MHz, and in the Compatibility Mode mode decreased to 1.031 MHz. To calculate the average rate we took only the central regions of the graphs.

At the same time we fixed the GPU voltage, you can spend a few parallels with the clock frequency. In the case of drivers and Radeon Software 16.7.1 Mode Compatibility Mode AMD was able to reduce the voltage with decreasing frequency. Between Radeon Software 16.6.2 and 16.7.1 is almost no difference. Although the voltage Radeon Software 16.7.1 is still a little higher in the central region.

Review Radeon RX 480 - analysis of energy consumption and performance with new driver and option Compatibility Mode

Equally important power GPU, we also reflected on the chart. Between Radeon Software 16.6.2 and 16.7.1 is almost no difference, but in the case of driver Radeon Software 16.7.1 with Compatibility Mode mode power consumption is much lower.

As the average value of GPU power consumption also clearly shows that the AMD driver Radeon Software 16.7.1 Compatibility Mode mode and significantly reduced power consumption. Of course, GPU is a major contributor to power consumption video card, but also should take into account other components.

To estimate the total energy consumption video card, we turn to the results of tests of our colleagues from Tom’s Hardware. They clearly demonstrate the changes that have occurred in the mode Compatibility Mode Driver Radeon Software 16.7.1. Total power consumption is only partially reflects the picture, so it is interesting to look at the individual line voltages. And there can be clearly seen, as AMD was able to solve the problem.

Earlier, the PCI Express graphics card slot consume up to 6.7 A, but AMD has been able to reduce this level to 5.9 and 5.6 A. As a result, AMD was able to fit into the slot specification.

We conducted several tests to evaluate the performance. Judging by the results, with driver settings Radeon Software 16.7.1 default performance degradation does not occur, and when you turn on Compatibility Mode drop is not significant.

Conclusion

Frankly, we do not know why AMD did not notice the additional power consumption via PCI Express slot on the stage of development and testing of the video card. Subsystem video card power might well have to change, but apparently affected by some other factors.

On the positive side, we note a fast AMD reaction that, eventually, could resolve the problem. AMD is directly related to editors, the first to notice the problem. AMD did not gloss over the issue, officially acknowledging its existence. A few days later the decision was presented to the driver means.

Members are free to decide whether they need a Compatibility Mode is activated or not. Without the active mode, the graphics card is unlikely to pose a threat to the motherboard, the more that AMD was able to reduce energy consumption through the slot in the new driver. But the card is still active without the Compatibility Mode option does not fit the specifications. Nothing wrong with that, given the possible tolerances. Of course, AMD partners certainly will bypass this problem by simply setting the 8-pin power connector and the appropriate allocation of the power load.

Review Radeon RX 480 – analysis of energy consumption and performance with new driver and option Compatibility Mode was last modified: July 17th, 2016 by Casey Rembrandt