主题：【新闻速递】第二代Xbox硬件配置已经出台。 -- Highway

Although the architecture of the two consoles is quite different, the Xbox 2 has the processing power to emulate the Xbox, according to Microsoft. Whether the next-generation console will be backward compatible involves a variety of factors, not the least of which is the massive development and testing effort required to allow Xbox games run on Xenon.

Xenon is a big-endian system. Both the CPU and GPU process memory in big-endian mode. Games ported from little-endian systems such as the Xbox or PC need to account for this in their game asset pipeline, the Microsoft’s engineer notes.

Tapping into the power of the CPU is a daunting task. Writing multithreaded game engines is not trivial. Xenon system software is designed to take advantage of this processing power wherever possible. The Xbox Advanced Technology Group (ATG) is also exploring a variety of techniques for offloading graphics work to the CPU.

Below scoops from the document are published.

Xbox 2 May Process up to 6 Threads

The Xbox 2’s central processing unit is a custom processor based on PowerPC technology. The CPU includes three independent processors (cores) on a single die. Each core runs at 3.50GHz speed of faster. The Xbox 2 microprocessor can issue two instructions per clock cycle per core. At peak performance, Xenon can issue 21 billion instructions per second.

The chip for Microsoft’s future console was designed by IBM in close consultation with the Xbox team, leading to a number of revolutionary additions, including a dot product instruction for extremely fast vector math and custom security features built directly into the silicon to prevent piracy and hacking.

Each core has two symmetric hardware threads (SMT), for a total of six hardware threads available to games. Not only does the “Xenon CPU” include the standard set of PowerPC integer and floating-point registers (one set per hardware thread), the microprocessor also includes 128 vector (VMX) registers per hardware thread. This astounding number of registers can drastically improve the speed of common mathematical operations, according to the document.

Each of the three cores includes a 32KB L1 instruction cache, a 32KB L1 data cache and share a 1MB L2 cache. The L2 cache can be locked down in segments to improve performance. The L2 cache also has the very unusual feature of being directly readable from the GPU, which allows the GPU to consume geometry and texture data from L2 and main memory simultaneously.

Microsoft claims that instructions of the next-generation console are exposed to games through compiler intrinsic, allowing developers to access the power of the chip using C language notation.

Xbox 2 Graphics Processor to Use Shader Model 3.0

The graphics processor designed for the Xbox 2 console is a custom 500MHz chip from ATI Technologies.

The shader core has 48 Arithmetic Logic Units (ALUs) that can execute 64 simultaneous threads on groups of 64 vertices or pixels. ALUs are automatically and dynamically assigned to either pixel or vertex processing depending on load. The ALUs can each perform one vector and one scalar operation per clock cycle, for a total of 96 shader operations per clock cycle. Texture loads can be done in parallel to ALU operations. At peak performance, the GPU can issue 48 billion shader operations per second.

The GPU has a peak pixel fillrate of 4 or more gigapixels/sec (16 gigasamples/sec with 4x antialiasing). The peak vertex rate is 500 or more million vertices/sec. The peak triangle rate is 500 or more million triangles/sec. Microsoft reportedly states that the figures are attainable with non-trivial shaders.

Microsoft’s future console is designed for HDTV output. In order to fit 720p frame-buffer inside the chip, a special 10MB or larger on-die embedded dynamic RAM (EDRAM) buffer will be incorporated. Larger frame-buffers are also possible because of hardware-accelerated partitioning and predicated rendering that has little cost other than additional vertex processing. Along with the extremely fast EDRAM, the GPU also includes hardware instructions for alpha blending, z-test, and antialiasing.

The Xbox 2 graphics architecture is a unique design that implements a superset of Direct3D version 9.0. It includes a number of important extensions, including additional compressed texture formats and a flexible tessellation engine. Xenon not only supports high-level shading language (HLSL) model 3.0 for vertex and pixel shaders but also includes advanced shader features well beyond model 3.0, Microsoft claims. For instance, shaders use 32-bit IEEE floating-point math throughout. Vertex shaders can fetch from textures, and pixel shaders can fetch from vertex streams. Xenon shaders also have the unique ability to directly access main memory, allowing techniques that have never before been possible.

As with Xbox, Xenon will support precompiled push buffers (“command buffers” in Xenon terminology), but to a much greater extent than the Xbox console does. The Xbox team is exposing and documenting the command buffer format so that games are able to harness the GPU much more effectively.

In addition to an extremely powerful GPU, Xenon also includes a very high-quality resize filter. This filter allows consumers to choose whatever output mode they desire. Xenon automatically scales the game’s output buffer to the consumer-chosen resolution.

Xbox 2 Memory to Pump up to 22.4GB of Data per Second

The Xbox 2 will have 256MB or more of unified memory, equally accessible to both the GPU and CPU.

The main memory controller resides on the GPU (the same as in the Xbox architecture). It has 22.4GB/sec or higher aggregate bandwidth to RAM, distributed between reads and writes. Aggregate means that the bandwidth may be used for all reading or all writing or any combination of the two. Translated into game performance, the GPU can consume a 512×512×32-bpp texture in only 47 microseconds.

The front side bus (FSB) bandwidth peak is 10.8GB/sec for reads and 10.8GB/sec for writes, over 20 times faster than for Xbox. Note that the 22.4GB/sec main memory bandwidth is shared between the CPU and GPU. If, for example, the CPU is using 2GB/sec for reading and 1GB/sec for writing on the FSB, the GPU has 19.4GB/sec available for accessing RAM.

Eight pixels (where each pixel is colour plus z = 8 bytes) can be sent to the EDRAM every GPU clock cycle, for an EDRAM write bandwidth of 32GB/sec. Each of these pixels can be expanded through multisampling to 4 samples, for up to 32 multi-sampled pixel samples per clock cycle. With alpha blending, z-test, and z-write enabled, this is equivalent to having 256GB/sec of effective bandwidth! The important thing is that frame buffer bandwidth will never slow down the Xbox 2 GPU.

New Audio Format for Xbox 2

The Xbox 2 central processing unit is a superb processor for audio, particularly with its massive mathematical horsepower and vector register set. The microprocessor can process and encode hundreds of audio channels with sophisticated per-voice and global effects, all while using a fraction of the power of a single CPU core.

The system’s south bridge also contains a key hardware component for audio ?C XMA decompression. XMA is the native Xenon compressed audio format, based on the WMA Pro architecture. XMA provides sound quality higher than ADPCM at even better compression ratios, typically 6:1?C12:1. The south bridge contains a full silicon implementation of the XMA decompression algorithm, including support for multi-channel XMA sources. XMA is processed by the south bridge into standard PCM format in RAM. All other sound processing (sample rate conversion, filtering, effects, mixing, and multispeaker encoding) happens on the CPU.

The lowest-level Xbox 2 audio software layer is XAudio, a new API designed for optimal digital signal processing. The Xbox Audio Creation Tool (XACT) API from Xbox is also supported, along with new features such as conditional events, improved parameter control, and a more flexible 3D audio model.

No Built-in Wi-Fi in Xbox 2

As with Xbox, the next-generation console code-named Xenon is designed to be a multiplayer console. It has built-in networking support including an Ethernet 10/100-BaseT port. It supports up to four controllers.

From an audio/video standpoint, Xenon will support all the same formats as Xbox, including multiple high-definition formats up through 1080i, plus VGA output.

In order to provide greater flexibility and support a wider variety of attached devices, the Xenon console includes standard USB 2.0 ports. This feature allows the console to potentially host storage devices, cameras, microphones, and other devices.

Xbox 2 Unlikely to Feature HDD

The Xenon console is designed around a larger world view of storage than Xbox was. Games will have access to a variety of storage devices, including connected devices (memory units, USB storage) and remote devices (networked PCs, Xbox Live). At the time of this writing, the decision to include a built-in hard disk in every Xenon console has not been made. If a hard disk is not included in every console, it will certainly be available as an integrated add-on component, Microsoft said.

Xenon supports up to two attached memory units (MUs). MUs are connected directly to the console, not to controllers as on Xbox. The initial size of the MUs is 64MB, although larger MUs may be available in the future. MU throughput is expected to be around 8MB/sec for reads and 1MB/sec for writes.

The Xenon game disc drive is a 12x DVD, with an expected outer edge throughput of 16MB/sec. Latency is expected to be in the neighbourhood of 100ms. The media format will be similar to Xbox, with approximately 6GB of usable space on the disk. As on Xbox, media will be stored on a single side in two 3GB layers.

Design Not Finalised

The Xenon industrial design process is well underway, but the final look of the box has not been determined. The Xenon console will be smaller than the Xbox console.

The standard Xbox 2 controller will have a look and feel similar to the Xbox controller. The primary changes are the removal of the Black and White buttons and the addition of shoulder buttons. The triggers, thumbsticks, D-pad, and primary buttons are essentially unchanged. The controller will support vibration.

Xenon Development Kit

The Xenon development environment follows the same model as for Xbox. Game development occurs on the PC. The resulting executable image is loaded by the Xenon development kit and remotely debugged on the PC. Microsoft Visual Studio version 7.1 continues as the development environment for Xenon.

The Xenon compiler is based on a custom PowerPC back end and the latest MS Visual C++ front end. The back end uses technology developed at MS for Windows NT on PowerPC. The Xenon software group includes a dedicated team of compiler engineers updating the compiler to support Xenon-specific CPU extensions. This team is also heavily focused on optimization work.

The Xenon development kit will include accurate DVD emulation technology to allow developers to very precisely gauge the effects of the retail console disc drive.

Representatives for Microsoft Corporation did not comment on the report.