View source for Defining ISAs (as of M5 2.0 beta 3)

==Overview==
First, make sure you have basic understanding of how an ISA description generates instructions within the M5 framework. A good start is the [[The M5 ISA description language]] page. 

For this example, we will be constructing an ISA called MyISA which will just be a renamed version of the MIPS ISA. We will go through the steps of creating the files
and configuration opions for an M5 ISA description.

Your new ISA description, MyISA, will need to generate correct instructions for the different CPU models. More specifically, your MyISA description will allow your MyISA
architecture (analagous to ALPHA,MIPS,SPARC,etc.) to be plugged into System-Call Emulation (SE) and Full-System (FS) simulations of any M5 CPU Model.

== Syscall Emulation (SE) MyISA ==

=== Creating the Files for MyISA ===
The correct place to insert your ISA files in M5 is in the src/arch directory. In this directory, create another directory called 'myisa' to keep your code.
For this example, we will copy the relevant files needed from the M5 MIPS ISA description.
<pre>
cd src/arch
mkdir myisa
cd myisa
cp -r ../mips/*.hh ./
cp -r ../mips/*.cc ./
</pre>

The relevant files are as follows:
* isa_traits.hh/cc - <explanation here>
* regfile.hh/cc, regfile/* - <explanation here>
* process.hh/cc -  <explanation here>
* linux/* -  <explanation here>
* isa/* -  <explanation here>
* faults.hh/cc - <explanation here>

You need to make sure that all instances of MipsISA needs to be replaced with MyISA in the files.
<pre>
perl -pe s/Mips/My/g ????
</pre>

=== Making M5 Recognize MyISA ===
* m5/build_opts/MYISA_SE - Create this file that allows M5 to recognize MyISA as a Syscall Emulation build option. It's contents should contain:
<pre>
TARGET_ISA = 'myisa'
FULL_SYSTEM = 0
</pre>

* m5/src/arch/isa_specific.hh - Edit this file by adding a constant for MyISA and then adding MyISA to the #define if/else structure. 
<pre>
...
#define ALPHA_ISA 21064
...
#define MY_ISA 6400

...

#if THE_ISA == ALPHA_ISA
    #define TheISA AlphaISA
#elif THE_ISA == SPARC_ISA
    #define TheISA SparcISA
...
#elif THE_ISA == MY_ISA
    #define TheISA MyISA
#else
    #error "THE_ISA not set"
#endif

</pre>

* m5/src/arch/myisa/SConsopts - Edit the file so that the SCons build system will recognize your ISA
<pre>
Import('*')

all_isa_list.append('myisa')
</pre>

=== MyISA Decoding & Instruction Object Creation - src/arch/MyISA/isa/*  ===
At this point, the next major component for defining your own ISA is setting up the MyISA decoder. Please refer to the [[ISA_description_system | ISA description page]] for detailed specifics of 
the instruction object decoding and construction process.

We'll go over the files you will be using for your MyISA description here:
* isa/*
** operands.isa
** base.isa
** decoder.isa
** main.isa
** includes.isa
* isa/formats/*
** formats.isa
** basic.isa
** int.isa
** branch.isa  
** control.isa  
** fp.isa  
** mem.isa  
** noop.isa  
** tlbop.isa  
** trap.isa  
** unimp.isa  
** unknown.isa  
** util.isa

=== Testing MyISA ===
'''Test That your decoder builds:'''
<pre>
scons build/MYISA_SE/arch/MyISA/atomic_simple_cpu_exec.cc CPU_MODELS=AtomicSimpleCPU
</pre>