OP_IMMED_B_SRC
FIELD_PREP(OP_IMMED_B_SRC, breg) |
reg = FIELD_GET(OP_IMMED_B_SRC, instr);
*instr &= ~FIELD_PREP(OP_IMMED_B_SRC, 0xff);
*instr |= FIELD_PREP(OP_IMMED_B_SRC, immed & 0xff);