@Override
	public void initialExecuteCallback(Emulate emulate, Address current_address,
			RegisterValue contextRegisterValue) throws LowlevelError {
		if (TModeReg == null) {
			return; // Thumb mode not supported
		}
		BigInteger tModeValue = BigInteger.ZERO;
		if (contextRegisterValue != null) {
			tModeValue =
				contextRegisterValue.getRegisterValue(TModeReg).getUnsignedValueIgnoreMask();
		}
		if (!BigInteger.ZERO.equals(tModeValue)) {
			tModeValue = BigInteger.ONE;
		}
		emu.getMemoryState().setValue(TBreg, tModeValue);
	}
Initialize TB register based upon context-register state before first instruction is
executed.
Ghidra/Processors/ARM/src/main/java/ghidra/program/emulation/ARMEmulateInstructionStateModifier.java