Altera 50G Interlaken MegaCore Function - Manual (Page 37)

During the SOP cycle (labeled with data value d1) and the cycle that follows the SOP cycle (labeled with
data value d2), you must hold the value of
itx_num_valid[2:0]
at 3'b100. In the following clock cycle,
labeled with data value d3, you must hold the following values on critical input signals to the IP core:
•
itx_num_valid[2:0]
at the value of 3'b011 to indicate the current data symbol contains three 64-bit
words of valid data.
•
itx_eopbits[3]
high to indicate the current cycle is an EOP cycle.
•
itx_eopbits[2:0]
at the value of 3'b011 to indicate that only three bytes of the final valid data word
are valid data bytes.
This signal behavior correctly transfers a data packet with the total packet length of 83 bytes to the IP core,
as follows:
• In the SOP cycle, the IP core receives 32 bytes of valid data (d1).
• In the following clock cycle, the IP core receives another 32 bytes of valid data (d2).
• In the third clock cycle, the EOP cycle, the IP core receives two full words (2 x 8 = 16 bytes) and three
bytes of valid data, for a total of 19 valid bytes.
The total packet length is 32 + 32 + 19 = 83 bytes.
50G Interlaken IP Core Back-Pressured Packet Transfer Example
Figure 4-6: Packet Transfer on Transmit Interface with Back Pressure
This example illustrates the expected behavior of the 50G Interlaken application interface transmit signals
during a packet transfer with back pressure.
tx_usr_clk
itx_sop
itx_chan
itx_sob
itx_eob
itx_din_words
itx_num_valid
itx_eopbits
itx_ready
itx_calendar
Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6 Cycle 7 Cycle 8 Cycle 9
8’h2
d1 d2 d3
3’b100 3’b100 3’b100
4’b0000
d4
3’b000 3’b100
64’hffff_ffff_ffff_ffff 64’h1111_2222_3333_4444
In this example, the 50G Interlaken IP Core accepts the first four data symbols (128 bytes) of a data
packet. The clock cycles in which the application transfers the data values d2 and d3 to the 50G Interlaken
IP Core are grace-period cycles following the 50G Interlaken IP Core's de-assertion of
itx_ready
.
The 50G Interlaken IP Core supports up to 4 cycles of grace period, enabling you to register the input data
and control signals, as well as the
itx_ready
signal, without changing functionality. The grace period
UG-01140
2015.05.04
50G Interlaken IP Core Back-Pressured Packet Transfer Example 4-11
Functional Description Altera Corporation
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