UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
557 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
23.9.1.2 Current dTD pointer descriptor fields
The current dTD pointer is used by the device controller to locate the transfer in progress.
This word is for device controller (hardware) use only and should not be modified by DCD
software.
23.9.1.3 Transfer overlay descriptor fields
The seven DWords in the overlay area represent a transaction working space for the
device controller. The general operational model is that the device controller can detect
whether the overlay area contains a description of an active transfer. If it does not contain
an active transfer, then it will not read the associated endpoint.
Table 434. Endpoint capabilities and characteristics
Access Bit
Name
Description
RO
31:30 MULT
Number of packets executed per transaction descriptor
00 - Execute N transactions as demonstrated by the USB variable
length protocol where N is computed using Max_packet_length
and the Total_bytes field in the dTD.
01 - Execute one transaction
10 - Execute two transactions
11 - Execute three transactions
Remark:
Non-isochronous endpoints must set MULT = 00.
Remark:
Isochronous endpoints must set MULT = 01, 10, or 11
as needed.
RO
29
ZLT
Zero length termination select
This bit is used for non-isochronous endpoints to indicate when a
zero-length packet is received to terminate transfers in case the
total transfer length is “multiple”.
0 - Enable zero-length packet to terminate transfers equal to a
multiple of Max_packet_length (default).
1 - Disable zero-length packet on transfers that are equal in
length to a multiple Max_packet_length.
RO
28:27 - reserved
RO
26:16 Max_packet
_length
Maximum packet size of the associated endpoint (<= 1024)
RO
15
IOS
Interrupt on setup
This bit is used on control type endpoints to indicate if USBINT is
set in response to a setup being received.
RO
14:0
-
reserved
Table 435. Current dTD pointer
Access
Bit
Name
Description
R/W
(hardware
only)
31:5
Current_TD_pointer Current dTD pointer
This field is a pointer to the dTD that is represented in
the transfer overlay area. This field will be modified by
the device controller to the next dTD pointer during
endpoint priming or queue advance.
-
4:0
-
reserved