I wonder if the bit 22 has some function in instructions like LDRH, STRH, LDRSBT, LDRD, ... (bits 27, 26, 25 = 0, 0, 0)?
In some instructions, like LDR, STR, LDRB (bits 27, 26, 25 = 0, 1, 1) , I understand, it chooses between byte and word access.
I've seen that.It looks like new command groups are added in best fit manner to keep the instruction set fragmentation low.