NXP Semiconductors LPC24XX UM10237 - Manual (Page 383)

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User manual Rev. 04 — 26 August 2009 383 of 792
NXP Semiconductors
UM10237
Chapter 13: LPC24XX USB device controller
14.7 Auto Length Transfer Extraction (ATLE) mode operation
Some host drivers such as NDIS (Network Driver Interface Specification) host drivers are
capable of concatenating small USB transfers (delta transfers) to form a single large USB
transfer. For OUT USB transfers, the device hardware has to break up this concatenated
transfer back into the original delta transfers and transfer them to separate DMA buffers.
This is achieved by setting the DMA mode to Auto Transfer Length Extraction (ATLE)
mode in the DMA descriptor. ATLE mode is supported for Bulk endpoints only.
OUT transfers in ATLE mode
Fig 49. Isochronous OUT endpoint operation example
DMA_mode Next_DD_Valid Isochronous_endpoint Max_packet_size DMA_buffer_length
0 16 31
after 4 packets
15 0x60000010
0x80000035
0x000A0010
0x4
0x0
W1
W2
W3
W4
W0
FULL
EMPTY
data memory
packet size memory
0x60000000
0x80000000
W1
W2
W3
W4
W0
0 0 1 0x0 0x000A
Next_DD_Pointer
NULL
DMA_buffer_start_addr
Isocronous_packetsize_memory_address
DD_Retired DD_Status Packet_Valid ATLE settings Present_DMA_Count
0x0 0 NA NA 0x0
Packet_Length frame_ number Packet_Valid
10
15
8
20
1
1
1
1
21
22
23
24
0 0x1 - -