EE Registers

General-Purpose Registers (GPRs)

As per MIPS tradition, the EE has 32 GPRs. Notably, they are all 128-bit, though the full 128 bits are only used in certain instructions.

Name	Convention
zero	Hardwired to 0, writes are ignored
at	Temporary register used for pseudo-instructions
v0-v1	Return register, holds values returned by functions
a0-a3	Argument registers, holds first four parameters passed to a function
t0-t7	Temporary registers. t0-t3 may also be used as additional argument registers
s0-s7	Saved registers. Functions must save and restore these before using them
t8-t9	Temporary registers
k0-k1	Reserved for use by kernels
gp	Global pointer
sp	Stack pointer
fp	Frame pointer
ra	Return address. Used by JAL and (usually) JALR to store the address to return to after a function

Aside from zero, all GPRs may be freely accessed if convention rules are respected.

Special Registers

Name	Purpose
pc	Program counter, address of currently-executing instruction (32-bit)
hi/lo	Stores multiplication and division results (64-bit)
hi1/lo1	Used by MULT1/DIV1 type instructions, same as above (64-bit)
sa	Shift amount used by QFSRV instruction