The Standard ABI, Coprocessors

r0   a1
r1   a2
r2   a3
r3   a4
r4   v1
r5   v2
r6   v3
r7   v4
r8   v5
r9   v6
r10  v7
r11  v8
r12  ip
r13  sp
r14  lr
r15  pc


Role of registers
A registers are function arguments (caller-saved)
V registers are callee-saved
R12 is the "intra-procedure scratch"
R13 is the stack pointer (software defined)
R14 is the link register (hardware defined)
R15 is the program counter (hardware defined)

Coprocessors
The architecture defines 16 coprocessors
CP15, if present, is used for cache and MMU
CP0 and CP1, if present, are used for FPU
The following instructions are defined by the architecture:
Register move CPU/coprocessor: MRC, MCR
Coprocessor load and store: LDC, STC
Coprocessor data processing: CDP