Serial Lite IV Intel® FPGA IP User Guide

ID 683655
Date 12/01/2021
Public
Document Table of Contents

3.1.1. TX MAC Adapter

The TX MAC adapter controls the data transmission to the user logic using the Avalon® streaming interface. This block supports user-defined information transmission and flow control.

Transferring User-defined Information

In Full mode, the IP provides the tx_is_usr_cmd signal that you can use to initiate user-defined information cycle such as XOFF/XON transmission to the user logic. You can initiate the user-defined information transmission cycle by asserting this signal and transfer the information using tx_avs_data along with the assertion of tx_avs_startofpacket and tx_avs_valid signals. The block then deasserts the tx_avs_ready for two cycles.

Note: The user-defined information feature is available only in Full mode.

Flow Control

There are conditions where the TX MAC is not ready to receive data from the user logic such as during link re-alignment process or when there is no data available for transmission from the user logic. To avoid data loss due to these conditions, the IP uses the tx_avs_ready signal to control the data flow from the user logic. The IP deasserts the signal when the following conditions occur:
  • When tx_avs_startofpacket is asserted, tx_avs_ready is deasserted for one clock cycle.
  • When tx_avs_endofpacket is asserted, tx_avs_ready is deasserted for one clock cycle.
  • When any paired CWs is asserted tx_avs_ready is deasserted for two clock cycles.
  • When RS-FEC alignment marker insertion occurs at the custom PCS interface, tx_avs_ready is deasserted for four clock cycles.
  • Every 17 Ethernet core clock cycles in PAM4 modulation mode and every 33 Ethernet core clock cycles in NRZ modulation mode. The tx_avs_ready is deasserted for one clock cycle.
  • When user logic deasserts tx_avs_valid during no data transmission.
The following timing diagrams are examples of TX MAC adapter using tx_avs_ready for data flow control.
Figure 5. Flow Control with tx_avs_valid Deassertion and START/END Paired CWs
Figure 6. Flow Control with Alignment Marker Insertion
Figure 7. Flow Control with START/END Paired CWs Coincide with Alignment Marker Insertion

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