Extremely nerdy sub-detail -- M-profile actually has all the handling for the Thumb-to-Arm switch architecturally, with the LSB of a branch target being signifi

Extremely nerdy sub-detail -- M-profile actually has all the handling for the Thumb-to-Arm switch architecturally, with the LSB of a branch target being significant and a T bit in the PSR to tell you what mode you're in, which you can set to 0. It's just that attempting to actually execute an insn with PSR.T==0 will trigger a UsageFault :-) (The CPU is even required to fetch the insn from memory first -- a MPU fault will take precedence over the T-bit-clear fault.)