Most of the instructions are 32-bit size, only the Variable-Length Encoding (VLE) group is smaller in order to provide a higher code density for embedded applications. All instructions are split into the following three categories:
- Defined: All of the instructions are defined in the Power ISA books.
- Illegal: Available for future extensions of the Power ISA. An attempt to execute them will invoke the illegal instruction error handler.
- Reserved: Allocated to specific purposes that are outside the scope of the Power ISA. An attempt to execute them will either perform an implemented action or invoke the illegal instruction error handler if the implementation is not available.
Bits 0 to 5 always specify the opcode, and many instructions also have an extended opcode. A large number of instruction formats are supported; here are some examples:
- I-FORM [OPCD+LI+AA+LK]
- B-FORM [OPCD+BO+BI+BD+AA+LK]
Each instruction field has its own abbreviation and meaning; it makes sense...
