UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 375 o f 792
NXP Semiconductors UM10237
Chapter 13: LPC24XX 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
(Section 13–11.3).
14.4 The DMA descriptor
DMA transfers are described by a data structure called the DMA Descriptor (DD).
DDs are placed in the USB RAM. These descriptors can be located anywhere in the USB
RAM at word-aligned addresses. USB RAM is part of the system memory that is used for
the USB purposes. It is located at address 0x7FD0 0000 and is 8 kB in size.
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
Table13–357 lists the DMA descriptor fields.
Table 357. DMA descriptor
Word
position Access
(H/W) Access
(S/W) Bit
position Description
0 R R/W 31:0 Next_DD_pointer (USB RAM address)
1 R R/W 1:0 DMA_mode (00 -Normal; 01 - ATLE)
R R/W 2 Next _DD _valid (1 - valid; 0 - invalid)
--3Reserved
R R/W 4 I sochronous_endpoint (1 - isochronous;
0 - non-isochronous)
R R/W 15:5 Max_packet_size
R/W[1] 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