USB HS/FS Device Controller
CPPI 4.1
Main
Memory
CPPI
DMA
(CDMA)
CDMA
Scheduler
(CDMAS)
SSRAM/
PPU
Transfer
DMA
(XDMA)
Endpoint
FIFOs
CPU
Queue
Manager
Interrupts
Queue Indicators
FIFO_full
FIFO_empty
FIFO_full
FIFO_empty
cdma_sreq
cdma_sready
DMA_req[8]
Configuration rd/wr
USB bus
RXCQ
RXSQ
Mentor
USB 2.0
Core
Queue push/
pop operations
Queue
push/pop
operations
Preliminary
Communications Port Programming Interface (CPPI) 4.1 DMA
www.ti.com
Figure 20-20. Receive USB Data Flow Example (Initialization)
20.4.9.2.3 CDMA Transfers Data from SSRAM / PPU to Main Memory for Receive (Step 3)
1. The CDMAS see FIFO_empty de-asserted (there is RX data in the FIFO) and issues a transaction
credit to the CDMA.
2. The CDMA begins packet reception by fetching the first PBD from the Queue Manager using the
Free Descriptor / Buffer Queue 0 (Rx Submit Queue) index that was initialized in the RX port DMA
state for that channel.
3. The CDMA will then begin writing the 64-byte block of packet data into this DB.
4. The CDMA will continue filling the buffer with additional 64-byte blocks of data from the CPPI FIFO
and will fetch additional PBD as needed using the Free Descriptor / Buffer Queue 1, 2, and 3
indexes for the 2nd, 3rd, and remaining buffers in the packet. After each buffer is filled, the CDMA
writes the buffer descriptor to main memory.
20.4.9.2.4 CDMA Completes the Packet Transfer for Receive (Step 4)
1. After the entire packet has been received, the CDMA writes the packet descriptor to main memory.
2. The CDMA then writes the packet descriptor to the RXCQ specified in the Queue Manager / Queue
Number fields in the RX Global Configuration Register.
3. The Queue Manager then indicates the status of the RXCQ to the CPU via an interrupt.
4. The CPU can then process the received packet by popping the received packet information from the
RXCQ and accessing the packet’s data from main memory.
1818
Universal Serial Bus (USB)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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