Preliminary
Communications Port Programming Interface (CPPI) 4.1 DMA
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Table 20-8. Packet Descriptor Word 1 (PD1) Bit Field Descriptions
Bits
Field Name
Description
This field indicates the port number (0-31) from which the packet
31-27
Source Tag; Port #
originated. The DMA overwrites this field on packet reception. This is the
RX Endpoint number from which the packet originated.
This field indicates the channel number within the port from which the
26-21
Source Tag; Channel #
packet originated. The DMA overwrites this field on packet reception. This
field is always 0-67.
This field indicates the sub-channel number (0-31) within the channel from
20-16
Source Tag: Sub-channel #
which the packet originated. The DMA overwrites this field on packet
reception. This field is always 0.
15-0
Destination Tag
This field is application-specific. This field is always 0.
Table 20-9. Packet Descriptor Word 2 (PD2) Bit Field Descriptions
Bits
Field Name
Description
This bit indicates if an error occurred during reception of this packet (0 =
no error occurred; 1 = error occurred). The DMA overwrites t his field on
31
Packet error
packet reception. Additional information about different errors may be
encoded in the protocol specific fields in the descriptor.
This field indicates the type of this packet. The CPU initializes this field for
30-26
transmitted packets; the DMA overwrites this field on packet reception.
This field is encoded as:
5 = USB
8-31 = Reserved
25-20
Reserved
Reserved
If a zero-length USB packet is received, the XDMA will send the CDMA a
data block with a byte count of 0 and this bit is set. The CDMA will then
19
Zero-length packet indicator
perform normal EOP termination of the packet without transferring data.
For transmit, if a packet has this bit set, the XDMA will ignore the CPPI
packet size and send a zero-length packet to the USB controller.
This field contains protocol-specific flags/information that can be assigned
18-16
Protocol-specific
based on the packet type. Not used for USB.
This field indicates the return policy for this packet. The CPU initializes
15
Return policy
this field.
0 = Entire packet (still linked together) should be returned to the queue
specified in bits 13-0.
1 = Each buffer should be returned to the queue specified in bits 13-0 of
Word 2 in their respective descriptors. The Tx DMA will return each buffer
in sequence.
This field indicates whether or not this descriptor is in a region which is in
14
On-chip
on-chip memory space (1) or in external memory (0).
This field indicates which queue manager in the system the descriptor is
to be returned to after transmission is complete. This field is not altered by
31-12
Packet return queue mgr #
the DMA during transmissionor reception and is initialized by the CPU.
There is only one queue manager in the USB HS/FS device controller.
This field must always be 0.
This field indicates the queue number within the selected queue manager
that the descriptor is to be returned to after transmission is complete. This
11-0
Packet return queue #
field is not altered by the DMA during transmission or reception and is
initialized by the CPU.
Table 20-10. Packet Descriptor Word 3 (PD3) Bit Field Descriptions
Bits
Field Name
Description
31-22
Reserved
Reserved
The buffer length field indicates how many valid data bytes are in the
21-0
Buffer 0 length
buffer. The CPU initializes this field for transmitted packets; the DMA
overwrites this field on packet reception.
1798Universal Serial Bus (USB)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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