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Lexikon

AMD 29000

A ref="module.php?name=Lexikon&file=search&eid=1&query=RISC">RISC ref="module.php?name=Lexikon&file=search&eid=1&query=microprocessor">microprocessor descended from the ref="module.php?name=Lexikon&file=search&eid=1&query=Berkley RISC">Berkley RISC design. Like the ref="module.php?name=Lexikon&file=search&eid=1&query=SPARC">SPARC design that was introduced shortly afterward, the 29000 has a large {register set} split into local and global sets. But though it was introduced before the SPARC, it has a more elegant method of register management. The 29000 has 64 global registers, in comparison to the SPARC' s eight. In addition, the 29000 allows variable sized windows allocated from the 128 register stack ref="module.php?name=Lexikon&file=search&eid=1&query=cache">cache. The current window or stack frame is indicated by a stack pointer, a pointer to the caller' s frame is stored in the current frame, like in an ordinary stack (directly supporting stack languages like ref="module.php?name=Lexikon&file=search&eid=1&query=C">C, a ref="module.php?name=Lexikon&file=search&eid=1&query=CISC">CISC-like philosophy). Spills and fills occur only at the ends of the cache, and registers are saved/loaded from the memory stack. This allows variable window sizes, from 1 to 128 registers. This flexibility, plus the large set of global registers, makes ref="module.php?name=Lexikon&file=search&eid=1&query=register allocation">register allocation easier than in SPARC. There is no special ref="module.php?name=Lexikon&file=search&eid=1&query=condition code register">condition code register - any general register is used instead, allowing several condition codes to be retained, though this sometimes makes code more complex. An ref="module.php?name=Lexikon&file=search&eid=1&query=instruction prefetch">instruction prefetch buffer (using ref="module.php?name=Lexikon&file=search&eid=1&query=burst mode">burst mode) ensures a steady instruction stream. Branches to another stream can cause a delay, so the first four new instructions are cached - next time a cached branch (up to sixteen) is taken, the cache supplies instructions during the initial memory access delay. Registers aren' t saved during interrupts, allowing the interrupt routine to determine whether the overhead is worthwhile. In addition, a form of register access control is provided. All registers can be protected, in blocks of 4, from access. These features make the 29000 useful for embedded applications, which is where most of these processors are used, allowing it the claim to be "the most popular RISC processor". The 29000 also includes an ref="module.php?name=Lexikon&file=search&eid=1&query=MMU">MMU and support for the ref="module.php?name=Lexikon&file=search&eid=1&query=AMD 29027">AMD 29027 ref="module.php?name=Lexikon&file=search&eid=1&query=FPU">FPU. (1995-06-19)

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Free On-line Dictionary of Computing

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