Functional Description
16.3.9.9.1.3 USB 2.0 Core Transmits USB Packets for Tx (Step 3)
1. Once the XDMA has transferred enough 64-byte blocks of burst of data from the CPPI FIFO to fill the
Endpoint FIFO (accumulated 512 bytes), it signals the Mentor USB 2.0 Core that a TX packet is ready
(sets the endpoint’s TxPktRdy bit).
2. The USB 2.0 Core will transmit the packet from the Endpoint FIFO out on the USB BUS when it
receives a corresponding IN request from the attached USB Host.
3. After the USB packet is transferred, the USB 2.0 Core issues a TX DMA_req to the XDMA.
4. This process is repeated until (the above steps ‘1’, ‘2’, and ‘3’) the entire packet has been transmitted.
The XDMA will also generate the required termination packet depending on the termination mode
configured for the endpoint.
16.3.9.9.1.4 Return Packet to Completion Queue and Interrupt CPU for Tx (Step 4)
1. After all data for the packet has been transmitted (as specified by the packet size field), the CDMA will
write the pointer of the Packet Descriptor only to the TX Completion Queue specified in the return
queue manager / queue number fields of the packet descriptor.
2. The Queue Manager then indicates the status of the TXSQ (empty) to the CDMAS and the TXCQ to
the CPU via an interrupt.
16.3.9.9.2 Receive USB Data Flow Using DMA
The receive buffer descriptors and queue status configuration prior to the transfer taking place is shown in
.
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SPRUH73H – October 2011 – Revised April 2013
Universal Serial Bus (USB)
Copyright © 2011–2013, Texas Instruments Incorporated