AMD’s new Zen 4 CPUs for Socket AM5 – Temperature and power management of Raphael explained in detail | Exclusive

1 - Thermisches Management 2 - Power Management

The Power Management

The power management features allow the processor to deliver maximum performance and stay within the specified power supply and power consumption limits. The basic idea is to define only a small number of P-states visible to the operating system: a base P-state, a lower P-state, and a so-called 3rd P-state. Condition. However, the entire frequency range supported by the processor is defined by much finer-grained P-states (FGPS).

A combination of a PLL with 25 MHz resolution and a digital frequency synthesizer is used for this purpose. “Skin Temperature Aware Power Management” – STAPM for short – is AMD’s solution to keeping mobile devices at a comfortable operating temperature, and in this case, completely disabled.

It is important to note that certain power management features such as Package Power Tracking (PPT) can increase the power consumption of typical applications to beyond the TDP of the processor! This power limit, up to which the component can consume power beyond the TDP, is defined as the so-called PPT limit.

The PPT limit can be changed during runtime via the BIOS. Incidentally, it’s interesting how AMD handles passing defaults internally, as the BIOS (simplistically speaking) multiplies everything by 1.35 to set the new PPT limit. However, for safety, there are internal checks that prevent a PPT limit from being set that is higher than the default value. However, any PPT limit lower than the default PPT limit can be set.

Basics of power control (voltage transformer)

Here, too, a lot can be saved or, unfortunately, wasted in return. However, AMD has long set clear guidelines for optimizing the component selection and implementation of newly developed systems. In addition to considering what is active for each mode and what needs to be powered, the overall efficiency of the power distribution network also plays a very important role in the platform’s ability to meet these high-level requirements.

This also and especially applies to the introduction of the new AM5 platform. Of course, the highest possible power efficiency must already be taken into account in the design phase. Attempts to modify an existing platinum design in order to increase energy efficiency usually do not lead to the desired results. BIOS improvements alone also do not bring the maximum benefit. The greatest gain is only achieved if the hardware is designed with maximum efficiency in mind and the choice of components used takes all this into account.

AMD points out to avoid excessive levels (stages) of power conversion when generating partial voltages in order to maintain efficiency and not push the overall efficiency down too much. The topology of the power conversion must therefore be carefully examined in advance. The number and level of voltages as well as the current requirements for each of these rails must meet the requirements. If the current requirement is high, switching regulators must be used that are sufficiently high. The total number of stages in the current path should be limited to two, including the main input power supply, because each stage significantly reduces the overall efficiency of the final voltage supplied. Series connection of power supplies are therefore always extremely counterproductive. Exceptions here are only the reference voltages, which have to follow another voltage, or if the current is exceptionally low, for example.

Efficiencies and power supply

The efficiency of the system can not be higher than the efficiency of the installed power supply in the computer, that is of course logical. It must be large enough to provide stable power to all peripherals and expansion cards to be connected, but must not be so large that efficiency drops off in a typical system configuration due to insufficient load. All power supplies have efficiency curves and if the current load is zero, then the efficiency is also zero.

Most current PC power supplies offer their maximum efficiency at a load of over 80%. Another important area for power supplies with multiple outputs is the effect on overall efficiency when the individual outputs are loaded differently (crossload).  The power supplies have three operating ranges:
– Underloaded
– Properly loaded
– Overloaded

AMD provides an example of the power efficiency curves showing the three areas. An extreme case is when the load current is zero, since the efficiency is also zero.

Even if I always get beaten up when I write about the sense or rather nonsense of very heavily oversized power supplies – it hardly makes any sense in total, since the systems almost never run constantly at full load and the curve thus always shifts into the area of too small loads.

Summary

It is difficult to break down many of the important details to a common denominator that even an end user can relate to. For the typical PC user and self-builder it is in any case first of all interesting how AMD defines and uses the value for Tctl (although the junction temperatures are certainly much higher) and one also protects the end user from panic with normalized values. And it is also a uniform size for all TDP classes to realize cross-class regulation (fan) and control.

The explanations about thermal management should give the user a certain feeling of security today, because a CPU does not “burn out” so easily anymore, those times are gone, thank God. The small excursion to Tcase shows by the way that one should rather not orient oneself at this value. The power management confirms once again what we already know from Zen 3, up to the fine gradation of the FGPS and thus also the very variable clock rates.

The part with the power supply (power supply, motherboard) I have included for a good reason, because I had already observed some efficiency failures in some motherboard tests in the past. You should never forget that AMD’s processors are real SoCs and you can’t easily compare the performance values with those of Intel, especially at idle. In the branch of the CPU (EPS) hang now once more function groups.

I hope it wasn’t boring, nor too complex. Much of what AMD writes about Raphael we already know in this or a similar form. However, it’s also reassuring to know that AMD is continuing on the same path, so you already know roughly what to expect on these points. So you won’t have to do any serious rethinking, and that’s a good thing.

Sources: AMD, Intel (via leaks)