Word 0 (Reserved)
Word 1 (Reserved)
Buffer Information Word 0 (Buffer Length)
Buffer Information Word 1 (Buffer Pointer)
Linking Information (Next Descriptor Pointer)
Original Buffer Information Word 1 (Original Buffer Pointer)
Required Information
(32 Bytes)
Word 2 [Pkt Info] Reserved
Original Buffer Information Word 0 (Original Buffer Pointer)
Word 2 [Buffer Info]
Functional Description
The buffer descriptor layout is shown in
and described within
through
.
Figure 16-14. Buffer Descriptor (BD) Layout
Table 16-17. Buffer Descriptor Word 0 (BD0) Bit Field Descriptions
Bits
Field Name
Description
31-0
Reserved
Reserved
Table 16-18. Buffer Descriptor Word 1 (BD1) Bit Field Descriptions
Bits
Field Name
Description
31-0
Reserved
Reserved
Table 16-19. Buffer Descriptor Word 2 (BD2) Bit Field Descriptions
Bits
Field Name
Description
31-15
Reserved
Reserved
This field indicates whether or not this descriptor is in a region which is
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
13-12
Packet return queue mgr #
the DMA during transmission or reception and is initialized by the CPU.
There is only 1 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 16-20. Buffer Descriptor Word 3 (BD3) 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 upon packet reception.
1739
SPRUH73H – October 2011 – Revised April 2013
Universal Serial Bus (USB)
Copyright © 2011–2013, Texas Instruments Incorporated