5.1. TX MAC Interface to User Logic
The TX MAC provides an Avalon® streaming interface to the FPGA fabric. The minimum packet size is nine bytes.
|clk_txmac||Output||Clock for the TX logic. Derived from pll_refclk, and is an output from the Low Latency 50G Ethernet IP core. clk_txmac is guaranteed to be stable when tx_lanes_stable is asserted. The frequency of this clock is 390.625 MHz.All TX MAC interface signals are synchronous to clk_txmac.|
|l2_tx_data[127:0]||Input||Data Input to MAC. Bit 127 is the MSB and bit 0 is the LSB. Bytes are read in the usual left to right order.
The Low Latency 50G Ethernet core does not process incoming frames of less than nine bytes correctly. You must ensure such frames do not reach the TX client interface.
You must send each TX data packet without intermediate idle cycles. Therefore, you must ensure your application can provide the data for a single packet in consecutive clock cycles. If data might not be available otherwise, you must buffer the data in your design and wait to assert l2_tx_startofpacket when you are assured the packet data to send on l2_tx_data[127:0] is available or will be available on time.
|l2_tx_preamble[63:0]||Input||User preamble data. Available when you select PREAMBLE PASS-THROUGH mode.
User logic drives the custom preamble data when l2_tx_startofpacket is asserted.
|l2_tx_valid||Input||When asserted, indicates valid data is available on l2_tx_data[127:0]. You must assert this signal continuously between the assertions of l2_tx_startofpacket and l2_tx_endofpacket for the same packet.|
|l2_tx_startofpacket||Input||When asserted, indicates the first byte of a frame. When l2_tx_startofpacket is asserted, the MSB of l2_tx_data drives the first byte of the packet.|
|l2_tx_endofpacket||Input||When asserted, indicates the end of a packet. The IP core ignores packets with length less than nine bytes.|
|l2_tx_empty[3:0]||Specifies the number of empty bytes on l2_tx_data when l2_tx_endofpacket is asserted.|
|l2_tx_ready||Output||When asserted, indicates that the MAC can accept the data.|
|l2_txstatus_valid||Output||When asserted, indicates that l2_txstatus_error[6:0] is driving valid data.|
|l2_txstatus_data[39:0]||Output||Specifies information about the transmit frame. The following fields are defined:
|l2_txstatus_error[6:0]||Output||Specifies the error type in the transmit frame. The following fields are defined: