ARM Registers
9/7/2007
The ARM microprocessor has 16 general-purpose registers.
THUMB has eight general-purpose registers, R0-R7, and access to the high registers, R8-R15.
The following table shows the assigned register roles.
| Register | Description |
|---|---|
R0 |
Argument1, Return Value Temporary register |
R1 |
Argument2, Second 32-bits if double or 64-bit int return value Temporary register |
R2-R3 |
Arguments Temporary registers |
R4-R10 |
R7 is THUMB frame pointer Permanent registers. |
R11 |
ARM frame pointer Permanent register |
R12 |
Temporary register |
R13 |
Stack pointer Permanent register |
R14 |
Link register Permanent register |
R15 |
Program Counter |
Note that registers R0 through R3 hold the first four words of incoming arguments. The microprocessor constructs remaining arguments in the calling function's argument build area, which does not provide space into which R0 through R3 can be spilled.
The following table shows additional predefined registers for Vector Floating Point (VFP) and for WMMX.
| Register | Description |
|---|---|
s0-s31 |
VFP single-precision registers. Registers s16-s31 are permanent registers. |
d0-d15 |
VFP double-precision registers. Registers d8-d15 are permanent registers. |
fpsid |
VFP system ID register |
fpscr |
VFP status and control register |
fpexc |
VFP exception register |
wr0-wr16 |
WMMX SIMD data registers |
wc0-wc16 |
WMMX status and control registers |
wcid |
WMMX coprocessor ID register, synonymous with wc0 |
wcon |
WMMX control register, synonymous with wc1 |
wcssf |
WMMX saturation SIMD flags, synonymous with wc2 |
wcasf |
WMMX arithmetic SIMD flags, synonymous with wc3 |
wcgr0-wcgr3 |
WMMX control general-purpose registers, synonymous with wc8-wc11 |