Altera Low Latency 40-Gbps Ethernet MAC and PHY MegaCore Function - Manual (Page 92)

Signal Name Direction Description
tx_in_zero_tcp
Input New signal in 14.1 release. The TX client asserts this signal during
a TX SOP cycle to tell the IP core to zero the TCP checksum in the
current packet.
A zeroed TCP checksum indicates the checksum value is not
necessarily correct. This information is useful when the correct
TCP checksum has not yet been recalculated after the packet is
modified.
tx_in_tcp_
offset[15:0]
Input Indicates the byte offset of the TCP checksum in the current
packet. The TX client must ensure this signal has a valid value
during each TX SOP cycle when it also asserts the
tx_in_zero_
tcp
signal. Holds the byte offset of the two bytes in the packet that
the IP core should reset.
The TX client must ensure that the TCP checksum bytes and the
timestamp bytes in the packet do not overlap. The IP core does
not check for overlap. If these two fields overlap, the results are
undefined.
ptp_pkt_out Output Indicates the current frame on the TX Ethernet interface is a 1588
PTP packet. The IP core asserts this signal for a single
clk_txmac
clock cycle when the frame begins transmission on the Ethernet
link.
tod_tx_clk_
st2[95:0]
Output Provides the timestamp when a 1588 PTP frame begins transmis‐
sion on the Ethernet link. Value is valid when the
ptp_pkt_out
signal is asserted. This signal is meaningful only in two-step clock
mode.
rx_tod[95:0] Output Whether or not the current packet on the RX client interface is a
1588 PTP packet, indicates the timestamp when the IP core
received the packet on the Ethernet link. The IP core provides a
valid value on this signal in the same cycle it asserts the RX SOP
signal for 1588 PTP packets.
PTP Timestamp Formats
The Low Latency 40-100GbE IP core supports a 96-bit timestamp (V2 format) or a 64-bit timestamp (V1
format), depending on the value of the
ptp_v2
field of the
TX_PTP_STATUS
register. If the IP core supports
a the V1 format, the IP core completes all processing in the V2 format and then outputs the appropriate
64 bits as the timestamp.
The IP core maintains the time-of-day (TOD) in V2 format:
• Bits [95:48]: Seconds (48 bits).
• Bits [47:16]: Nanoseconds (32 bits). This field overflows at 1 billion.
• Bits [15:0]: Fractions of nanosecond (16 bits). This field is a true fraction; it overflows at 0xFFFF.
The IP core expects to receive timestamps from the TOD module in V2 format.
UG-01172
2015.05.04
PTP Timestamp Formats 3-47
Functional Description Altera Corporation
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