Cyclone® V Hard Processor System Technical Reference Manual

ID 683126
Date 8/28/2023
Public
Document Table of Contents

19.5.4.2.1. IN Transactions

For an IN transaction, the application performs the following steps:

  1. Enables the endpoint
  2. Triggers the DMA engine to write the associated data packet to the corresponding transmit FIFO buffer
  3. Waits for the packet completion interrupt from the controller

When an IN token is received on an endpoint when the associated transmit FIFO buffer does not contain sufficient data, the controller performs the following steps:

  1. Generates an interrupt
  2. Returns a NAK handshake to the USB host

If sufficient data is available, the controller transmits the data to the USB host.