Arria V Hard Processor System Technical Reference Manual

ID 683011
Date 12/02/2022
Public
Document Table of Contents

19.4.1.9. DMA

The DMA has two modes of operation. You program your software to select between scatter-gather DMA mode or buffer DMA mode depending on the controllers function.

If the controller is functioning as a generic root hub, you should program your software to select the buffer DMA mode that supports split transfers.

If generic root hub functionality is not required, or if the controller is configured in Device mode, you can program your software to select scatter-gather DMA mode.

If you wish to dynamically switch the mode of operation based on the queried device status or capability, your software driver must cleanly switch between the two modes of operation. For example, you may want the controller to default to scatter-gather DMA mode and only change mode when it detects a generic HUB with fast-speed and low-speed capability. Some basic requirements for switching include:
  • A soft reset must be issued before changing modes.
  • If buffer DMA mode is selected, then the Host mode periodic request queue depth must not be set to 16.
  • Devices must be re-enumerated.