Programmer’s Model

Note

Registers r0–r7 are known as the low registers. Registers r8–r15 are known as the high registers.

2.6.4Accessing high registers in Thumb state

In Thumb state, the high registers, r8–r15, are not part of the standard register set. The assembly language programmer has limited access to them, but can use them for fast temporary storage.

You can use special variants of the MOV instruction to transfer a value from a low register, in the range r0–r7, to a high register, and from a high register to a low register. The CMP instruction allows you to compare high register values with low register values. The ADD instruction enables you to add high register values to low register values. For more details, please refer to the ARM Architecture Reference Manual.