Nxp semiconductors – NXP Semiconductors LPC24XX UM10237 User Manual
Page 377
UM10237_4
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 04 — 26 August 2009
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NXP Semiconductors
UM10237
Chapter 13: LPC24XX USB device controller
[1]
Write only in ATLE mode
Legend: R - Read; W - Write; I - Initialize
14.4.1 Next_DD_pointer
Pointer to the memory location from where the next DMA descriptor will be fetched.
14.4.2 DMA_mode
Specifies the DMA mode of operation. Two modes have been defined: Normal and
Automatic Transfer Length Extraction (ATLE) mode. In normal mode, software initializes
the DMA_buffer_length for OUT endpoints. In ATLE mode, the DMA_buffer_length is
extracted from the incoming data. See
Section 13–14.7 “Auto Length Transfer Extraction
(ATLE) mode operation” on page 383
14.4.3 Next_DD_valid
This bit indicates whether the software has prepared the next DMA descriptor. If set, the
DMA engine fetches the new descriptor when it is finished with the current one.
14.4.4 Isochronous_endpoint
When set, this bit indicates that the descriptor belongs to an isochronous endpoint. Hence
5 words have to be read when fetching it.
14.4.5 Max_packet_size
The maximum packet size of the endpoint. This parameter is used while transferring the
data for IN endpoints from the memory. It is used for OUT endpoints to detect the short
packet. This is applicable to non-isochronous endpoints only. This field should be set to
the same MPS value that is assigned for the endpoint using the USBMaxPSize register.
3
R/W
R/I
0
DD_retired (To be initialized to 0)
W
R/I
4:1
DD_status (To be initialized to 0000):
0000 - NotServiced
0001 - BeingServiced
0010 - NormalCompletion
0011 - DataUnderrun (short packet)
1000 - DataOverrun
1001 - SystemError
W
R/I
5
Packet_valid (To be initialized to 0)
W
R/I
6
LS_byte_extracted (ATLE mode) (To be initialized to 0)
W
R/I
7
MS_byte_extracted (ATLE mode) (To be initialized to 0)
R
W
13:8
Message_length_position (ATLE mode)
-
-
15:14
Reserved
R/W
R/I
31:16
Present_DMA_count (To be initialized to 0)
4
R/W
R/W
31:0
Isochronous_packetsize_memory_address
Table 357. DMA descriptor
Word
position
Access
(H/W)
Access
(S/W)
Bit
position
Description