Microsoft's upcoming Xbox One gaming console will contain a custom chip the company designed in conjunction with Advanced Micro Devices with the aim of delivering maximum graphics performance, presenters said Monday at Microsoft's Hot Chips conference.
The high-performance, low-power chip has specialized processors beyond the CPU and GPU to handle tasks such as audio processing, video decode and encode and other small game characteristics. The system has 5 billion transistors, and uses an eight-core AMD CPU code-named Jaguar, which is also being used in the Sony's upcoming PlayStation 4. The graphics processor is a Radeon GPU that has been customized for the Xbox One, Microsoft presenters said at the conference in Stanford, California."Almost every aspect has been customized," said John Sell, a hardware architect at Microsoft.The Xbox One system chip also has 500GB of storage, 8GB of DDR3 memory and 47MB of on-die storage that could act as cache, where information will be stored temporarily. The GPU can provide more than a teraflop of peak performance.AMD's x86 CPUs are based on the Jaguar core, which was introduced for PCs, laptops and servers last year. The eight CPU cores are broken into clusters of four cores with a total of 4MB of L2 cache.
"We've made some alterations to the CPU clusters to support coherent bandwidth between clusters...and other processors," Sell said.
The graphics processor supports DirectX 11.1, which is Microsoft's graphics engine that will power games. Microsoft calls the engine 1-plus, a reference to unique control processor features for custom graphics and processing in the Xbox graphics core. "These have been customized to significantly reduce the amount of time, the amount of work, that the CPU has to spend when assembling graphics commands," Sell said. One unique aspect of the chip is a shared memory pool that can be accessed by CPUs, GPUs and other processors in the system. Typically, GPUs and CPUs have different memory systems, but the new features increase the overall addressable memory in the Xbox One. The GPUs and CPUs have also been modified to enable shared memory.Shared memory is also part of a specification being pushed by the HSA Foundation, which wants to blur the line between GPU and CPU memory to make programming easier. AMD is one of the founding members of the HSA Foundation, though Sony is also a member, which suggests that shared memory may also be part of PlayStation 4.
"We can let developers have access to direct programming on GPU without a lot of overhead," Sell said.
Overall, the system has been designed to balance bandwidth with the power requirements.
"An important aspect of that is letting CPU and GPU share memory spaces," Sell said.The coherency connections are a derivative of AMD's years-old HyperTransport technology. The bandwidth can sustain data transfers of 30GB per seconds. However, the data transfers vary depending on the component and also the distance between parts.The chip will be made by Taiwan Semiconductor Manufacturing Co. (TSMC) using the 28-nm process, Sell said.
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