User guide

• If LDR, LDM, or POP load to the pc, they set the Thumb bit in the CPSR to bit[0] of the value loaded to the pc.

You can use this to change instruction sets. This is particularly useful for returning from subroutines. The same

return instruction can return to either an ARM or Thumb caller.

For more information, see Assembler Guide

and ARM Architecture Reference Manual.

3.2.5 Labels in Thumb code

The linker distinguishes between labels referring to:

• ARM instructions

• Thumb instructions

• data.

When the linker relocates a value of a label referring to a Thumb instruction, it sets the least significant bit of the

relocated value. This means that a branch to a label can automatically select the appropriate instruction set. This

works if any of the following instructions are used for the branch:

• BX in ARM architecture v4T

• BX, BLX, or LDR in architecture v5T and above.

In previous releases of ADS and SDT, it was necessary to mark data in Thumb code with the DATA directive. This is

no longer necessary.

Interworking ARM and Thumb