[1] : The Free On-line Dictionary of Computing (27 SEP 03)

amd 29000
     
         a risc microprocessor descended from the
        berkley risc design.  like the 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 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 c, a 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 register allocation
        easier than in sparc.
     
        there is no special condition code register - any general
        register is used instead, allowing several condition codes to
        be retained, though this sometimes makes code more complex.
        an instruction prefetch buffer using 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 mmu and support for
        the amd 29027 fpu.
     
        1995-06-19
     
     
see also:
risc microprocessor berkley risc sparc register set cache 
c cisc register allocation condition code register instruction prefetch 
burst mode mmu amd 29027 fpu 

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