![Texas Instruments AM1808 Technical Reference Manual Download Page 1652](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_10945581652.webp)
Architecture
1652
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Serial Bus 2.0 (USB) Controller
Table 34-10. Host Packet Descriptor Word 2 (HPD Word 2)
Bits
Name
Description
31
Packet Error
This bit indicates if an error occurred during reception of this packet (0 = No error
occurred, 1 = Error occurred). The DMA overwrites this field on packet reception.
Additional information about different errors may be encoded in the protocol specific
fields in the descriptor.
30-26
Packet Type
This field indicates the type of this packet. The CPU initializes this field for transmitted
packets; the DMA overwrites this field on packet reception. This field is encoded as:
5 = USB
8-31 = Reserved
25-20
Reserved
Reserved
19
Zero-length packet indicator
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 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.
18-16
Protocol Specific
This field contains protocol specific flags/information that can be assigned based on
the packet type. Not used for USB.
15
Return Policy
This field indicates the return policy for this packet. The CPU initializes 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.
14
On-chip
This field indicates whether or not this descriptor is in a region which is in on-chip
memory space (1) or in external memory (0).
13-12
Packet Return Queue Mgr #
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 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.
11-0
Packet Return Queue #
This field indicates the queue number within the selected queue manager that the
descriptor is to be returned to after transmission is complete. This field is not altered
by the DMA during transmission or reception and is initialized by the CPU.
Table 34-11. Host Packet Descriptor Word 3 (HPD Word 3)
Bits
Name
Description
31-22
Reserved
Reserved
21-0
Buffer 0 Length
The Buffer Length field indicates how many valid data bytes are in the buffer. The
CPU initializes this field for transmitted packets; the DMA overwrites this field on
packet reception.
Table 34-12. Host Packet Descriptor Word 4 (HPD Word 4)
Bits
Name
Description
31-0
Buffer 0 Pointer
The Buffer Pointer is the byte aligned memory address of the buffer associated with
the buffer descriptor. The CPU initializes this field for transmitted packets; the DMA
overwrites this field on packet reception.
Table 34-13. Host Packet Descriptor Word 5 (HPD Word 5)
Bits
Name
Description
31-0
Next Descriptor Pointer
The 32-bit word aligned memory address of the next buffer descriptor in the packet. If
the value of this pointer is zero, then the current buffer is the last buffer in the packet.
The CPU initializes this field for transmitted packets; the DMA overwrites this field on
packet reception.