amd 29000

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amd 29000 - Free On-line Dictionary of Computing (26 May 2007) :

  AMD 29000
  
     <processor> 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)