Design an instruction using Thumb-2
There isn't a single solution to such an assignment. The general idea is


for each instruction group, determine how many bits are needed for the info within the group. For instance, 14 arithmetic 2-register instructions need a 4-bit code and two 4-bit register specifications, for a total of 12 bits.
the remaining bits are used to distinguish between the groups. Use short encodings for groups that need most bits.
place same type of bits fields in the same places, this eases decoding.