39 lines
1.6 KiB
Plaintext
39 lines
1.6 KiB
Plaintext
|
> README.Cygnus
|
||
|
|
-------------------------------------------------------------------------------
|
||
|
|
|
||
|
|
The following are the main reasons for constructing the simulator as a
|
||
|
|
generator:
|
||
|
|
|
||
|
|
1) Avoid large fixed decode source file, with lots of #ifs controlling
|
||
|
|
the compilation. i.e. keep the source cleaner, smaller and easier
|
||
|
|
to parse.
|
||
|
|
|
||
|
|
2) Allow optimum code to be created, without run-time checks on
|
||
|
|
instruction types. Ensure that the simulator engine only includes
|
||
|
|
code for the architecture being targetted. e.g. This avoids
|
||
|
|
run-time checks on ISA conformance, aswell as increasing
|
||
|
|
throughput.
|
||
|
|
|
||
|
|
3) Allow updates to the instruction sets to be added quickly. Having a
|
||
|
|
table means that the information is together, and is easier to
|
||
|
|
manipulate. Having the table generate the engine, rather than the
|
||
|
|
run-time parse the table gives higher performance at simulation
|
||
|
|
time.
|
||
|
|
|
||
|
|
4) Keep all the similar simulation code together. i.e. have a single
|
||
|
|
place where, for example, the addition code is held. This ensures that
|
||
|
|
updates to the simulation are not spread over a large flat source
|
||
|
|
file maintained by the developer.
|
||
|
|
|
||
|
|
-------------------------------------------------------------------------------
|
||
|
|
|
||
|
|
To keep the simulator simple (and to avoid the slight chance of
|
||
|
|
mis-matched files) the manifests describing an engine, and the
|
||
|
|
simulator engine itself, are held in the same source file.
|
||
|
|
|
||
|
|
This means that the engine must be included twice, with the first pass
|
||
|
|
controlled by the SIM_MANIFESTS definition.
|
||
|
|
|
||
|
|
-------------------------------------------------------------------------------
|
||
|
|
> EOF README.Cygnus
|