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UM10198
Philips Semiconductors
Chapter 10: USB device controller
Table 193. DMA descriptor …continued
Word position Access
(H/W)[1]
3
Access
Bit position Description
(S/W)
R/W
R/I
0
DD_retired (To be initialized to 0).
W
R/I
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.
4
[1]
R/W
R/I
5
Packet_valid (To be initialized to 0).
R/W
R/I
6
LS_byte_extracted (ATLE mode) (To be initialized to 0).
R/W
R/I
7
MS_byte_extracted (ATLE mode) (To be initialized to 0).
R
W
13:8
Message_length_position (ATLE mode).
-
-
15:14
Reserved.
R/W
R/I
31:16
Present_DMA_count (To be initialized to 0).
R/W
R/W
31:0
Isochronous_packetsize_memory_address
R - Read; W - Write; W* - Write only in ATLE mode; I - Initialize
3.9.1 Next_DD_pointer
Pointer to the memory location from where the next DMA descriptor has to be fetched.
3.9.2 DMA_mode
Defines in which mode the DMA has to operate. Two modes have been defined, Normal
and ATLE. In the normal mode the DMA engine will not split a packet into two different
DMA buffers. In the ATLE mode splitting of the packet into two buffers can happen. This is
because two transfers can be concatenated in the packet to improve the bandwidth. See
Section 10–4.3.2 “Concatenated transfer (ATLE) mode operation” on DMA operation.
3.9.3 Next_DD_valid
This bit indicates whether the software has prepared the next DMA descriptor. If it is valid,
the DMA engine once finished with the current descriptor will load the new descriptor.
3.9.4 Isochronous_endpoint
The descriptor belongs to an isochronous endpoint. Hence, 5 words have to be read.
3.9.5 Max_packet_size
This field is the maximum packet size of the endpoint. This parameter has to be used
while transferring the data for IN endpoints from the memory. It is used for OUT endpoints
to detect the short packet. This is applicable to non-isochronous endpoints only. The
max_packet_size field should be the same as the value set in the MaxPacketsize register
for the endpoint.
UM10198_1
User manual
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Rev. 01 — 1 June 2006
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