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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
228 of 808
NXP Semiconductors
UM10360
Chapter 11: LPC17xx USB device controller
In DMA mode, the bits corresponding to Interrupt on NAK for Bulk OUT and Interrupt OUT
endpoints (INAK_BO and INAK_IO) should be set to 0 using the SIE Set Mode command
(
).
15.4 The DMA descriptor
DMA transfers are described by a data structure called the DMA Descriptor (DD).
DDs are placed in RAM. These descriptors can be located anywhere in on-chip RAM at
word-aligned addresses.
DDs for non-isochronous endpoints are four words long. DDs for isochronous endpoints
are five words long.
The parameters associated with a DMA transfer are:
•
The start address of the DMA buffer
•
The length of the DMA buffer
•
The start address of the next DMA descriptor
•
Control information
•
Count information (number of bytes transferred)
•
Status information
lists the DMA descriptor fields.
Table 229. DMA descriptor
Word
position
Access
(H/W)
Access
(S/W)
Bit
position
Description
0
R
R/W
31:0
Next_DD_pointer
1
R
R/W
1:0
DMA_mode (00 -Normal; 01 - ATLE)
R
R/W
2
Next_DD_valid (1 - valid; 0 - invalid)
-
-
3
Reserved
R
R/W
4
Isochronous_endpoint (1 - isochronous;
0 - non-isochronous)
R
R/W
15:5
Max_packet_size
R/W
31:16
DMA_buffer_length
This value is specified in bytes for non-isochronous
endpoints and in number of packets for isochronous
endpoints.
2
R/W
R/W
31:0
DMA_buffer_start_addr