Altera Low Latency Ethernet 10G MAC - Manual (Page 38)

Overflow Handling
When an overflow occurs on the client side, the client can backpressure the Avalon-ST receive interface
by deasserting the
avalon_st_rx_ready
signal. If an overflow occurs in the middle of frame transmission,
the MAC RX truncates the frame by sending out the
avalon_st_rx_endofpacket
signal after the
avalon_st_rx_ready
signal is reasserted. The error bit,
avalon_st_rx_error[5]
, is set to 1 to indicate
an overflow. If there is an overflow during client data reception, the current frame will get truncated. The
MAC RX will drop the remaining payload of the erroneous frame and the subsequent frames if the
overflow condition persists. The MAC RX then continues to receive data when the overflow condition
ceases.
RX Timing Diagrams
Figure 3-15: Back-to-back Transmission of Normal Frames with CRC Removal Enabled
The following diagram shows back-to-back reception of normal frames with CRC removal enabled.
rx_312_5_clk
xgmii_rx_data[31:0]
xgmii_rx_control[3:0]
avalon_st_rx_startofpacket
avalon_st_rx_valid
avalon_st_rx_ready
avalon_st_trx_endofpacket
avalon_st_rx_data[31:0]
avalon_st_rx_empty[1:0]
avalon_st_rx_error[5:0]
avalon_st_rx_data[31:24]
avalon_st_rx_data[23:16]
avalon_st_rx_data[15:8]
avalon_st_rx_data[7:0]
xgmii_rx_data[7:0]
xgmii_rx_data[15:8]
xgmii_rx_data[23:16]
xgmii_rx_data[31:24]
* *fff * * * * *c 0000_0000 * 0faa_4s5e * * * * * * * * * *
1 0 1 f 0 1 f 0
* *fff *0 * * 0707_0707 * *0 0000_0000 * * * *
fb *ff cf 88 21 22 8cc 00 fd 07 fb 3a 00 c0 0a 4d da * cd 3a b6 fa 07 01 81 87 95 46 94 f2
88 ff 58 08 d3 be 88 00 07 07 88 3a 01 16 51 ae c5 * 40 3a df 55 80 00 f3 c7 46 df f6
88 d0 d5 cd a7 ff 00 07 07 88 3a 0a 50 51 2e 2b * 0a 3a 62 73 c2 46 97 24 43 aa
88 ad 49 f5 2a 00 07 07 88 d5 d9 6d 18 8d 57 * 7c d5 2b f1 00 3e 28 55 70 95
ff 61 68 03
5c 81 ff 60
fb ff 88 b6 07 22 8c 00 07 3a 01 c0 3a cf f1 21 00 fb
88 ff 08 df 07 be 89 00 07 3a 80 16 3a 58 55 d3 01 88
88 d5 62 07 a7 ff 00 07 3a c2 50 3a d0 73 cd 0a 88 ff 61
88 49 2b 07 2a 00 07 d5 00 6d d5 ad f1 f5 d9 88 ff 60
3-16 Overflow Handling
UG-01144
2014.12.15
Altera Corporation Functional Description of LL Ethernet 10G MAC
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