[binutils.git] / sim / mips / README.Cygnus

> README.Cygnus
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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.

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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.

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> EOF README.Cygnus
Commit	Line	Data
8ad57737 JSC	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