MIPS Assembly/Register File
Registers[edit | edit source]
MIPS has 32 general-purpose registers and another 32 floating-point registers. Registers all begin with a dollar-symbol ($). The floating point registers are named $f0, $f1, ..., $f31. The general-purpose registers have both names and numbers, and are listed below. When programming in MIPS assembly, it is usually best to use the register names.
|$0||$zero, $r0||Always zero|
|$1||$at||Reserved for assembler|
|$2, $3||$v0, $v1||First and second return values, respectively|
|$4, ..., $7||$a0, ..., $a3||First four arguments to functions|
|$8, ..., $15||$t0, ..., $t7||Temporary registers|
|$16, ..., $23||$s0, ..., $s7||Saved registers|
|$24, $25||$t8, $t9||More temporary registers|
|$26, $27||$k0, $k1||Reserved for kernel (operating system)|
Zero Register[edit | edit source]
The zero register ($zero or $0) always contains a value of 0. It is built into the hardware and therefore cannot be modified.
$at Register[edit | edit source]
The $at (Assembler Temporary) register is used for temporary values within pseudo commands. It is not preserved across function calls. For example, with the (slt $at, $a0, $s2) command, $at is set to one if $a0 is less than $s2, otherwise it is set to zero.
$v Registers[edit | edit source]
The $v Registers are used for returning values from functions. They are not preserved across function calls.
Argument Registers[edit | edit source]
The $a registers are used for passing arguments to functions. They are not preserved across function calls.
Temporaries[edit | edit source]
The temporary registers are used by the assembler or assembly language programmer to store intermediate values. They are not preserved across function calls.
Saved Temporaries[edit | edit source]
Saved Temporary registers are used to store longer lasting values. They are preserved across function calls.
$k Registers[edit | edit source]
The k registers are reserved for use by the OS kernel. They may change randomly at any time as they are used by interrupt handlers.
Pointer Registers[edit | edit source]
- Global Pointer ($gp) - Usually stores a pointer to the global data area (such that it can be accessed with memory offset addressing).
- Stack Pointer ($sp) - Used to store the value of the stack pointer.
- Frame Pointer ($fp) - Used to store the value of the frame pointer.
- Return Address ($ra) - Stores the return address (the location in the program that a function needs to return to).
All Pointer Registers are preserved across function calls.