ARM AND THUMB MODE SWITCH INSTRUCTIONS
This processor has two instruction encodings: ARM and THUMB.
IDA allows to specify the encoding mode for every single instruction.
For this IDA uses a virtual register T. If its value is zero, then
the ARM mode is used, otherwise the THUMB mode is used.
You can change the value of the register T using
the ‘change segment register value’ command
(the canonical hotkey is Alt-G)