sim/mips/README.Cygnus

   1 > README.Cygnus
   2 -------------------------------------------------------------------------------
   3
   4 The following are the main reasons for constructing the simulator as a
   5 generator:
   6
   7 1) Avoid large fixed decode source file, with lots of #ifs controlling
   8    the compilation. i.e. keep the source cleaner, smaller and easier
   9    to parse.
  10
  11 2) Allow optimum code to be created, without run-time checks on
  12    instruction types. Ensure that the simulator engine only includes
  13    code for the architecture being targetted. e.g. This avoids
  14    run-time checks on ISA conformance, aswell as increasing
  15    throughput.
  16
  17 3) Allow updates to the instruction sets to be added quickly. Having a
  18    table means that the information is together, and is easier to
  19    manipulate. Having the table generate the engine, rather than the
  20    run-time parse the table gives higher performance at simulation
  21    time.
  22
  23 4) Keep all the similar simulation code together. i.e. have a single
  24    place where, for example, the addition code is held. This ensures that
  25    updates to the simulation are not spread over a large flat source
  26    file maintained by the developer.
  27
  28 -------------------------------------------------------------------------------
  29
  30 To keep the simulator simple (and to avoid the slight chance of
  31 mis-matched files) the manifests describing an engine, and the
  32 simulator engine itself, are held in the same source file.
  33
  34 This means that the engine must be included twice, with the first pass
  35 controlled by the SIM_MANIFESTS definition.
  36
  37 -------------------------------------------------------------------------------
  38 > EOF README.Cygnus