about the altgx ip

now i am using the altgx ip for the SATA development.

According with the stx4_siv52001 user manual, in single width mode, the 8B/10B decoder's output should be 10bit. But in my simulation, why the transmitter's PCS module output is 20bit??? it means that 8B/10B decoder's outpout has been buffered , then transmitted to PMA module?

Anyone has the experience of altgx simulation? 3ks