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Philips Semiconductors
Volume 1
There are certain parameters associated with a DMA transfer. These are:
Table 235
Table 235: DMA descriptor
Word
position
0
1
2
3
4
Legend: R - Read; W - Write; I - Initialize
[1]
14.10.1 Next_DD_pointer
Pointer to the memory location from where the next DMA descriptor has to be fetched.
9397 750 XXXXX
User manual
•
The start address of the DMA buffer in the USB RAM.
•
The length of the DMA Buffer in the USB RAM.
•
The start address of the next DMA buffer.
•
Control information.
•
DMA count information (Number of bytes transferred).
•
DMA status information.
lists the DMA descriptor fields.
Access
Access
(H/W)
(S/W)
R
R/W
R
R/W
R
R/W
-
-
R
R/W
R
R/W
[1]
R/W
R/W
R/W
R/W
R/W
R/I
W
R/I
W
R/I
W
R/I
W
R/I
R
W
-
-
R/W
R/I
R/W
R/W
Write only in ATLE mode
Rev. 01 — 15 August 2005
Bit
Description
position
31:0
Next_DD_pointer (USB RAM address).
1:0
DMA_mode (00 -Normal; 01 - ATLE).
2
Next_DD_valid (1 - valid; 0 - invalid).
3
Reserved.
4
Isochronous_endpoint (1 - isochronous;
0 - non-isochronous).
15:5
Max_packet_size.
31:16
DMA_buffer_length in bytes.
31:0
DMA_buffer_start_addr.
0
DD_retired (To be initialized to 0).
4:1
DD_status (To be initialized to 0):
0000 - Not serviced.
0001 - Being serviced.
0010 - Normal completion.
0011 - Data under run (short packet).
1000 - Data over run.
1001 - System error.
5
Packet_valid (To be initialized to 0).
6
LS_byte_extracted (ATLE mode) (To be initialized to 0).
7
MS_byte_extracted (ATLE mode) (To be initialized to 0).
13:8
Message_length_position (ATLE mode).
15:14
Reserved.
31:16
Present_DMA_count (To be initialized to 0).
31:0
Isochronous_packetsize_memory_address.
UM10139
Chapter 14: USB Device Controller
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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