If channels A and CTRL both have TUSER with widths of 5 and 8 bits respectively, the output TUSER is a suitably delayed concatenation of A and CTRL TUSER fields, 13 bits wide, with A in the least significant 5 bit positions (4 down to 0).
If B and CTRL have TUSER widths of 4 and
10 respectively, but A has no TUSER, DOUT TUSER (m_axis_dout_tuser) has the bits of B_TUSER (s_axis_b_tuser) suitably delayed in positions 3 down to 0 with CTRL_TUSER (s_axis_ctrl_tuser) bits, suitably delayed, in positions 13
down to 4.