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In MIPS terminology, CP0 is the System Control Coprocessor (an essential part of the processor that is implementation-defined in MIPS I–V), CP1 is an optional floating-point unit (FPU) and CP2/3 are optional implementation-defined coprocessors (MIPS III removed CP3 and reused its opcodes for other purposes).
An opcode table (also called an opcode matrix) is a visual representation of all opcodes in an instruction set. It is arranged such that each axis of the table represents an upper or lower nibble, which combined form the full byte of the opcode. Additional opcode tables can exist for additional instructions created using an opcode prefix.
A more complex example is the MIPS encoding, which used only 6 bits for the opcode, followed by two 5-bit registers. The remaining 16 bits could be used in two ways, one as a 16-bit immediate value, or as a 5-bit shift value (used only in shift operations, otherwise zero) and the remaining 6 bits as an extension on the opcode.
Opcode for OR 0,0,0. [6] LDI 26,0: 4 0x34000034 Palindromic NOP - that is, an instruction that executes as NOP regardless of whether byte order is interpreted as little-endian or big-endian. Some PA-RISC system instructions are required to be followed by seven palindromic NOPs. [6] PowerPC: NOP: 4 0x60000000 (extended opcode for ori r0,r0,0)
This is the MIPS "Add Immediate" instruction, which allows selection of source and destination registers and inclusion of a small constant. On traditional architectures, an instruction includes an opcode that specifies the operation to perform, such as add contents of memory to register —and zero or more operand specifiers, which may specify ...
In some architectures, an instruction has a single opcode. In others, some instructions have an opcode and one or more modifiers. E.g., on the IBM System/370, byte 0 is the opcode but when byte 0 is a B2 16 then byte 1 selects a specific instruction, e.g., B205 16 is store clock (STCK).
In the early 1990s, MIPS began to license their designs to third-party vendors. This proved fairly successful due to the simplicity of the core, which allowed it to have many uses that would have formerly used much less able complex instruction set computer (CISC) designs of similar gate count and price; the two are strongly related: the price of a CPU is generally related to the number of ...
In the 6502, which has only a single arithmetic register A, this instruction can be represented entirely by its 8-bit opcode $06. [1] On processors with more registers, all that is needed is the opcode and register number, another 4 or 5 bits. On MIPS, for instance, the instruction needs only a 6-bit opcode and a 5-bit register number.