The s_axi_user_k_tx_tready signal is
asserted by the core and prioritized by CC, CB, NFC, and UFC messages. After asserting
s_axi_user_k_tx_tdata, the USER-K block number and
s_axi_user_k_tx_tvalid are asserted. If required,
the user application can change s_axi_user_k_tx_tdata
when s_axi_user_k_tx_tready is asserted (as shown in
the following figure). This action enables the Aurora 64B/66B core to select the
appropriate USER-K BTF from the nine USER-K blocks. The data available during the
assertion of s_axi_user_k_tx_tready is always
serviced.
Figure 1. Transmitting USER-K Data and USER-K Block Number
