H-Tile Ethernet Hard IP User Guide: For Intel® Stratix® 10 Devices

ID 683430
Date 1/18/2024
Public
Document Table of Contents

B.5.7. Retransmit Holdoff Quanta

Retransmit Holdoff Quanta

16b value specifying the holdoff time before XOFF is retransmitted when the corresponding Enable Automatic TX Pause Retransmission register bit is 1

Offset: 0x608

Access: RW

Retransmit Holdoff Quanta Fields

Bit Name Description Access Reset
15:0 holdoff_quanta Retransmit Holdoff Quanta
16b value specifying holdoff time before another XOFF is transmitted when the corresponding Enable Automatic TX Pause Retransmission register bit is 1
  • Times are programmed in holdoff quanta
    • For 100G links, 1 Holdoff Quanta = 2 clock cycles
  • Min value is 1, but to minimize wasted bandwidth, holdoff should be set as large as possible without exceeding the recommended max value
  • Max value for correct operation where holdoff retransmits PFC requests before the previously transmitted Quanta expires is:
    • For 100Gx4 links: corresponding pause/pfc quanta - (50 + Maximum TX Frame Size register value/32)
  • After power-on, holdoff_quanta defaults to 16'hFFFF
  • After i_cfg_rst_n, holdoff_quanta defaults to the value in the module parameter holdoff_quanta for pause, and pfc_holdoff_quanta_n for PFC
RW 0xFFFF