Original Buffer Information Word 1 (Original Buffer Pointer)
Original Buffer Information Word 0 (Original Buffer Length)
Linking Information (Next Descriptor Pointer)
Buffer Information Word 1 (Buffer Pointer)
Buffer Information Word 0 (Buffer Length)
Packet and Buffer Information Word 2
Packet Information Word 1
Packet Information Word 0
Optional Software-Specific Information
(2 Words (8 Bytes))
Optional Protocol-Specific Information
(0 to 64 Bytes in Multiples of 4 Bytes)
Optional Private Data
(Any Number of Bytes in Multiples of 4 Bytes)
Required Information
(32 Bytes)
Optional Information
(Not Required for USB)
Architecture
1651
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Serial Bus 2.0 (USB) Controller
Figure 34-16. Host Packet Descriptor Layout
Table 34-8. Host Packet Descriptor Word 0 (HPD Word 0)
Bits
Name
Description
31-27
Descriptor Type
The Host Packet Descriptor Type is 16 decimal (10h). The CPU initializes this field.
26-22
Protocol Specific Valid Word
Count
This field indicates the valid numberof 32-bit words in the protocol specific region. The
CPU initializes this field. This is encoded in increments of 4 bytes as:
0 = 0 byte
1 = 4 bytes
...
16 = 64 bytes
17-31 = Reserved
21-0
Packet Length
The length of the packet in bytes. If the Packet Length is less than the sum of the
buffer lengths, then the packet data will be truncated. A Packet Length greater than
the sum of the buffers is an error. The valid range for the packet length is 0 to (4M - 1)
bytes. The CPU initializes this field for transmitted packets; the DMA overwrites this
field on packet reception.
Table 34-9. Host Packet Descriptor Word 1 (HPD Word 1)
Bits
Name
Description
31-27
Source Tag: Port #
This field indicates the port number (0-31) from which the packet originated. The DMA
overwrites this field on packet reception. This is the RX Endpoint number from which
the packet originated.
26-21
Source Tag: Channel #
This field indicates the channel number within the port from which the packet
originated. The DMA overwrites this field on packet reception. This field is always 0-
67.
20-16
Source Tag: Sub-channel #
This field indicates the sub-channel number (0-31) within the channel from 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.