Nxp Semiconductors UM10237 用户手册

UM10237_2

© NXP B.V. 2008. All rights reserved.

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 
(

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

 lists the DMA descriptor fields. 

 

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)

-

-

3

Reserved

R

R/W

4

Isochronous_endpoint (1 - isochronous; 
0 - non-isochronous)

R

R/W

15:5

Max_packet_size

R/W

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