Detailed interpretation of the three known characteristics of PS5: frequency conversion, solid state and 3D audio
Sony disclosed the relevant core technical characteristics of PS5 some time ago, and explained the innovation and advantages of these technologies in detail. However, because it is a conference for professional understanding, these characteristics of PS5 now appear in many different interpretations. PS5 Chief Architect Mark Cerny (Mark Cerny) then contacted the well-known game technology analysis media Digital Foundry and talked with them about the details of these key technologies that have been announced, let us have a more on the PS5 hardware Detailed understanding.
Original title: PlayStation 5 uncovered: the Mark Cerny tech deep dive, Author: Richard Leadbetter.
Note: Because the original text involves many professional and technical details, in order to achieve a better reading effect, this article did a large-scale compilation, as simple and clear as possible.
Frequency conversion is to make the best use of things
The GPU frequency of PS5 surprised many people. The frequency of 2.23GHz is a very high frequency that is difficult for civilian PC graphics cards to reach, which makes most people doubt that this frequency is actually unreliable.
However, when we carefully consider Sony’s expression of CPU and GPU frequencies, we will find that things may not be simple.
The frequency of CPU and GPU marked by Sony for PS5 is the “limit” frequency, which means that its frequency will decrease. From our current understanding of the frequency conversion technology of PCs and mobile phones, is this not the performance degradation caused by overheating or overheating? From the past, we all tend to this kind of explanation.
But this time is not the same. The frequency reduction of PS5 is technically not caused by the fact that it is forced to decrease because of heat, but because of the active adjustment of the internal system. If the PS5 frequency drops due to overheating, the system performance is in an unreliable state, which is extremely unfriendly to developers.
Of course, Sony has taken this into consideration. With the help of AMD, the PS5 CPU and GPU maintain an overall controllable stable performance within their respective frequency ranges.
In general, devices such as PCs and mobile phones will set a temperature limit on the processor. Once the temperature exceeds or exceeds this temperature for a period of time, it will forcefully reduce the frequency in order to avoid overheating. In order to maintain the overall consistency of the game console, Sony does not limit the excessive temperature through the upper limit of temperature, but the upper limit of power consumption similar to notebook computers. The CPU power consumption plus the GPU power consumption will not exceed this upper limit. Under this wall of power consumption, the frequency of CPU and GPU will be changed by an adjustment algorithm.
Therefore, no matter whether the PS5 is placed in a refrigerator or in an ordinary room temperature environment, whether there is a slight deviation in the chip constitution at the time of shipment, it can have a uniform performance. After all, unified performance is a big premise for game consoles.
The author gives a simple example. This core is like a seesaw, with CPU and GPU at each end. The Sonys set their respective maximum heights for these two ends. No matter how the two change, the respective heights will not exceed this maximum height. CPUs and GPUs change from time to time, and the power consumption of their respective highest altitudes corresponds to the frequency data of 3.5GHz and 2.23GHz announced by Sony.
This rough diagram is just for easy understanding, Serny said that the minimum frequency will not be so low
This technology for the dynamic allocation of internal power consumption under stable overall power consumption is AMD ’s SmartShift for notebook platforms (coincidentally, Nvidia also recently announced a similar technology for its notebook platform, Dynamic Boost). For example, at some time when the CPU performance is excessive, it will transfer the power resources originally allocated to the CPU to the GPU, so that it can obtain a higher frequency, and vice versa.
Sony said the chip used to handle this power distribution task is integrated into the processing core. The sensitivity of this chip is extremely high, and even the slightest change in energy consumption can be immediately detected and responded to. After all, for the PS5 system, the power consumption of the CPU and GPU at a certain moment is very important data for developers.
Why do you say that? Although the PS5 is an overall stable system, its internal dynamic performance is different from the fixed performance of the traditional host and the rival model Xbox Series X, which requires game developers to adopt different optimization strategies for this dynamic performance. .
If you can modify the code to make the same frame number performance occur at lower power consumption, then this is a successful optimization.” That is to say Developers need to optimize the power consumption to make the performance stronger, so as to obtain more ideal results. The relationship between power consumption and frequency is non-linear, “under normal circumstances, for example, reducing power consumption by 10% will only cause the frequency to drop by a few percentage points (instead of also dropping by 10%).”
Since the system frequency is changing, why does Sony claim that the CPU or GPU can maintain or approach the limit frequency for most of the time? Serny’s explanation for this is the addition of a phenomenon called “race to idle”.
He gave an example. For example, when the game is running at 30 frames, the average rendering time of each frame is 33 milliseconds, but the GPU only took 28 milliseconds to complete the work, then the remaining 5 milliseconds is nothing to do. In the state of vertical synchronization, this is called “idle competition”. He said that it does not make sense to maintain a high frequency during these 5 milliseconds, which may mean that the GPU frequency of these 5 milliseconds may decrease in actual games.
But in order to give a statement on the GPU frequency, the situation of “idle competition” is added, and it becomes “the frequency that stays at or near the limit
Serny said a breakthrough for the team was to find a series of frequencies that keep the CPU and GPU energy densities consistent, convert these frequencies into locked performance descriptions, and put them in the development kit. Developers focus on optimization based on these frequency data without having to face complicated changing frequencies.
How is backwards compatibility implemented under such a system? We can review the design ideas of PS4 Pro in order to be compatible with PS4-“Butterfly Architecture”. The number of PS4 CU units was doubled, and the frequency was slightly increased. The CPU is still an eight-core Jaguar, but the frequency is increased a bit. When running the PS4 game, just turn off half of the CU unit and adjust it slightly.
The PS5 GPU is similarly processed, and the number of CU units is the same as the PS4 Pro. Judging from the previous leaked data, this GPU is compatible. When compatible, it will adjust the operating mode according to the respective conditions of PS4 Pro and PS4 to make it close to the original operating environment and reduce the difficulty of compatibility.
However, the CPU of PS5 has changed a lot this time, and the latest Zen 2 architecture is adopted, which may bring additional difficulty to compatibility. ”All games developed for Jaguar theoretically work well under Zen 2, but the timing of execution of instructions is basically different. We customized our Zen 2 core with AMD and added a difference for them The operating mode allows it to approach the execution time of Jaguar. ”
Serny said the team is still working on backwards compatible features. In addition, Sony has said that compatible games support enhanced, and how this enhanced effect remains to be tested by the actual machine.
The test data that was leaked at the beginning, the memory bandwidth of Gen2 mode has now been confirmed as 448GB / s
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Improving immersion is inseparable from solid state drives
The next generation of Sony and Microsoft chose solid-state drives as the main storage medium based on the feedback from the developers, and each made their own customized designs. PS5’s SSD throughput has reached 5.5GB / s, which has exceeded the speed of most solid state drives, which is undoubtedly a very proud achievement. So in addition to the increase in the loading speed of the hard disk, what else has it brought us?
The data transmission of PS5 mobilizes many components to work together, such as I / O processor, condensing engine, DMA controller, etc. The mechanism is relatively complex. However, Sony has provided developers with low-level and high-level access capabilities for developers to choose. There is a new I / O API at the bottom that allows developers to easily use its extreme speed, with low barriers and friendliness.
The file index of PS5 is no longer the traditional “file name + path” method, but is changed to an ID-based storage system, which makes file search faster. With a delay of a few milliseconds, the required files can be found and transmitted. These occur within the processing time of one frame, and even the worst case can be completed at most the next frame. If this is placed in a mechanical hard drive, this process will last as long as 250 milliseconds.
Cerney gave an example. For example, when an enemy dies and yells, even if the sound playback request is set as the first task at this time, it still probably takes 250 milliseconds, then the resulting sound delay will cause the immersion to decline. In similar scenarios, you need to respond quickly to reduce latency. The PS5 SSD will significantly improve this problem.
Developers do not need to care about these implementation technologies, just call the interface
Generational evolution of sound dimension
Voice is a key point for improvement in the next generation. Sony spent a lot of effort and energy on PS5 to enhance the immersion of the sound dimension.
There are two main changes. One is that PS5 supports hundreds of 3D sound sources, and hundreds of spatial sound sources support needless to say, which can better simulate real-life environmental sound sources. With a sound source, how can the sound simulate the effect of being transmitted from a certain coordinate position in space to the ear? This requires a second change point, the use of HRTF (Head Related Transfer Function, head related transfer function).
The knowledge related to HRTF technology is very professional and extensive. We only need to know that it is a function based on the spherical coordinate system with the human head as the coordinate origin, human head structure data, sound frequency and other information. Left ear and right ear.
The effect of HRTF is very good, but to achieve the most ideal effect needs to be customized according to the user’s own head data. It is obviously unrealistic for each player to customize their own HRTF. Sony’s approach is to provide five different HRTF effects at the time of launch, and the player himself chooses the most suitable one among these five.
Of course, this is only the current processing method. Serny said that this is an open research topic. Maybe in the future, players can send Sony their own head data, such as photos and videos, to customize it for themselves.
You can see that Mark Serny’s own customized HRTF image is not the same as the default
It is an engine named “Tempest” that handles these two points. Unlike PS4’s way of processing audio through the CPU, Tempest is a separate chip based on a CU (computing unit) of AMD GPU. It can be considered as a variant of GPU. Since its own principle is very similar to a continuous whole, the design goal can be achieved without any internal cache.
The team adopted the GPU type chip because the GPU itself was built specifically for multi-threaded tasks. Tempest supports two Wavefronts. One is for 3D audio and other system design functions, and the other is for games.”
However, due to more sound and related data to be processed, Tempest will occupy more than 20GB / s of bandwidth. This is not a small number, so developers need to pay attention to the Tempest bandwidth usage, if it is too high, it will have an adverse effect.
In addition, Tempest is compatible with another audio technology called Ambisonics, which now supports PS4 and PSVR. Serny said that the two can be mixed, for example, a very important sound can be processed by Tempest, and the main scene ambient sound can be processed by Ambisonics, to maximize the advantages of both to achieve satisfactory results.
However, 3D audio does not support all kinds of audio devices at the time of the first release. Sony chose to adapt it according to the amount of equipment. The standard headset is a device that was supported when it was first released. Currently, Sony is dealing with the optimization of TV speakers. The 5.1 and 7.1 sound systems need to be processed after the TV speakers are optimized. Slightly regret, Sony did not give an approximate support time for the latter two.
Although many specific technical details were announced, there are still many questions about the PS5 hardware itself. After all, the only thing we know so far is a “Spider-Man” loading time Demo running on an old version of the development machine, two interviews with “Wired” magazine, a Logo, an under-displayed handle, and a technical PPT.
In other words, we don’t even know the information of actually rendering game pixels on PS5. When the PS4 was first released, it brought a demo of “Killing Zone Shadow Fall”. The generational change is clear at a glance, and real game is always the best convincing. In addition, Sony calls the PS5 GPU as the RDNA 2 architecture, but some key technologies recently announced by the architecture, such as variable rate coloring, PS5 did not appear on the support list, which inevitably makes people doubt. The appearance of the main unit and the cooling system are also very curious.
All doubts can only be waited for Sony to release further information.