The Cell Broadband Engine in a simple analysis the Cell processor can be split into four components: external input and output structures, the main processor called the Power Processing Element (PPE) SMT eight fully-functional co-processors called the Synergistic Processing Elements or SPEs and a specialised high-bandwidth circular data bus connecting the PPE, input/output elements and the SPEs, called the Element Interconnect Bus or EIB.
The poweris achieved the high performance needed for mathematically intensive tasks, such as decoding/encoding MPEG streams, generating or transforming three dimensional data, or undertaking Fourier analysis of data, the Cell processor simply marries the SPEs and the PPE via the EIB to give both access to main memory or other external data storage. The PPE which is capable of running a conventional operating system has control over the SPEs and can start, stop, interrupt and schedule processes running on the SPEs. To this end the PPE has additional instructions relating to control of the SPEs. Despite having Turing complete architectures the SPEs are not fully autonomous and require the PPE to initiate them before they can do any useful work. Most of the "horsepower" of the system comes from the synergistic processing elements.
The PPE and bus architecture includes various modes of operation giving different levels of memory protection allowing areas of memory to be protected from access by specific processes running on the SPEs or PPE.
Both the PPE and SPE are RISC architectures with a fixed-width 32-bit instruction format. The PPE contains a 64-bit general purpose register set (GPR), a 64-bit floating point register set (FPR), and a 128-bit Altivec register set. The SPE contains 128-bit registers only. These can be used for scalar data types ranging from 8-bits to 128-bits in size or for SIMD computations on a variety of integer and floating point formats. System memory addresses for both the PPE and SPE are expressed as 64-bit values for a theoretic address range of 264 bytes. In practice, not all of these bits are implemented in hardware; the address space is extremely large nevertheless. Local store addresses internal to the SPU processor are expressed as a 32-bit word. In documentation relating to Cell a word is always taken to mean 32 bits, a doubleword means 64 bits, and a quadword means 128 bits.DMA MMU, and bus interface). An SPE is a RISC processor with 128-bit SIMD organization for single and double precision instructions. With the current generation of the Cell, each SPE contains a 256 KiB instruction and data local memory area (called "local store") which is visible to the PPE and can be addressed directly by software. Each SPE can support up to 4 GB of local store memory. The local store does not operate like a conventional CPU cache since it is neither transparent to software nor does it contain hardware structures that predict which data to load. The SPEs contain a 128 × 128 register file and measure 14.5 mm² on a 90 nm process. An SPE can operate on 16 8-bit integers, 8 16-bit integers, 4 32-bit integers, or 4 single precision floating-point numbers in a single clock cycle. It can also do a memory operation in the same clock cycle. Note that the SPU processor can not directly access system memory; the 64-bit memory addresses formed by the SPU must be passed from the SPU processor to the SPE memory flow controller (MFC) to set up a DMA operation within the system address space.set-top box might load programs for reading a DVD, video and audio decoding, and display, and the data would be passed off from SPE to SPE until finally ending up on the TV. Another possibility is to partition the input data set and have several SPEs performing the same kind of operation in parallel. At 3.2 GHz, each SPU gives a theoretical 25.6 GFLOPS of single precision performance.personal computer, the relatively high overall floating point performance of a Cell processor seemingly dwarfs the abilities of the SIMD unit in desktop CPUs like the Pentium 4 and the Athlon 64. However, comparing only floating point abilities of a system is a one-dimensional and application-specific metric. Unlike a Cell processor, such desktop CPUs are more suited to the general purpose software usually run on personal computers. In addition to executing multiple instructions per clock, processors from Intel and AMD feature branch predictors The Cell is designed to compensate for this with compiler assistance, in which prepare-to-branch instructions are created. For double-precision, as used in personal computers, Cell performance drops by an order of magnitude, but still reaches 14 GFLOPS.
Each SPE is composed of a "Synergistic Processing Unit", SPU, and a "Memory Flow Controller", MFC (
In one typical usage scenario, the system will load the SPEs with small programs chaining the SPEs together to handle each step in a complex operation. For instance, a
Compared to a modern
What does this all mean. The cell is made for multimedia the Spe's can be used for alot.
Log in to comment