This are the steps required to implement a new instruction.
Most of the instructions are already recognized, to do so 2 fields are required in each instruction class, for example the and instruction (which is in the module: armsim/instruction/dp.py) has the following fields:
testmask = 0b00001101111000000000000000000000
bitmask = 0b00000000000000000000000000000000
The testmask are the bits which need to be checked and the bitmask are those bits values, the operation executed to check if this is the right instruction is:
(instruction & testmask) == bitmask
If this returns true, the execute method is executed.
There are a number of utilities in the armsim.utils package, which you can use look for examples in the armsim/instruction/dp.py file! (this should be documented soon)