Intel® Stratix® 10 Hard Processor System Technical Reference Manual

ID 683222
Date 11/28/2022
Public

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18.6.3.2. Device Transaction

When configured as a device, the USB OTG controller uses a single FIFO buffer to receive the data for all the OUT endpoints. The receive FIFO buffer holds the status of the received data packet, including the byte count, the data packet ID (PID), and the validity of the received data. The DMA controller reads the data out of the FIFO buffer as the data are received. If a FIFO buffer overflow condition occurs, the controller responds to the OUT packet with a NAK, and internally rewinds the pointers.

For IN endpoints, the controller uses dedicated transmit buffers for each endpoint. The application does not need to predict the order in which the USB host accesses the nonperiodic endpoints. If a FIFO buffer underrun condition occurs during transmit, the controller inverts the cyclic redundancy code (CRC) to mark the packet as corrupt on the USB link.

The application handles one data packet at a time per endpoint in transaction‑level operations. The software receives an interrupt on completion of every packet. Based on the handshake response received on the USB link, the application determines whether to retry the transaction or proceed with the next transaction, until all packets in the transfer are completed.