To send an NFC message to a channel partner, the user application asserts
s_axi_nfc_tx_tvalid and writes an 8-bit pause
count to s_axi_nfc_tx_tdata[8:15]. The pause code
indicates the minimum number of cycles the channel partner must wait after receiving
an NFC message prior to resuming data send. The number of user_clk cycles without data is equal to s_axi_nfc_tx_tdata + 1.
When asserted, the s_axi_nfc_tx_tdata[7] signal indicates nfc_xoff, requesting that the channel partner stop sending data until
it receives a non-XOFF NFC message or reset. When a request is transmitted with
PAUSE and XOFF both set to 0, NFC is set to XON mode. To cancel XOFF mode, all 0s
(XON) should be transmitted. After the reception of this XON request, any new NFC
request is honored by the core. The user application must hold s_axi_nfc_tx_tvalid, s_axi_nfc_tx_tdata[8:15], and s_axi_nfc_tx_tdata[7] (nfc_xoff, if
used) until s_axi_nfc_tx_tready is asserted on a
positive user_clk edge indicating that the core can
transmit the NFC message.
Aurora 64B/66B cores cannot transmit data
while sending NFC messages. s_axi_tx_tready is
always deasserted on the cycle following an s_axi_nfc_tx_tready assertion. NFC Completion mode is available only
for the framing Aurora 64B/66B interface.