Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public
Document Table of Contents

5.1.6.10.3. Time-Based Scheduling

Time-based scheduling (TBS) feature is suitable for traffic whose periodicity and rate are predictable. This is an optional feature. To improve the quality-of-service of such traffic:

  • The transmit DMA fetches the packet from the host memory for transmission at designated time. This helps the software to setup the transmit descriptors in advance even before packet is ready/available. It reduces the overhead on the software and avoids constant monitoring of the time and helps in preparing descriptors just in time when the packet is targeted to be transmitted.
  • The MAC transmits the packet only at the designated/pre-determined time even if the packets are fetched in advance. This helps in maintaining a constant transmission rate that can be consumed by the receiver station; therefore avoiding congestion and excessive buffering in the network.

Description of Time-Based Scheduling

The time-based scheduling feature supports fetching and launching an Ethernet packet at (or after) a pre-determined time. The time-based scheduling is supported only in the following modes/configurations:
  • Full duplex mode
  • Link speed is 100Mbps or higher
  • MTL and higher configurations
  • Configurations in which time-stamping is enabled

Following are the time-based scheduling specific definitions:

  • Launch time - The time beyond which MTL can schedule the packet for transmission.
  • Fetch time - The time beyond which the Tx DMA can schedule a packet-fetch from the host memory.
  • Expiry time - The time beyond which the packet is dropped by MTL.
Note: Do not enable time-based scheduling (or enhanced descriptors) for the channel for which you enable the TSO or transmit timestamp control correction feature.

Enabling the Time-Based Scheduling Feature

Refer to the Setting up the Time-Based Scheduling Function in Programming Model for the EMAC for more information.