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BEOffset is the buffer end a1. Offset1 is used for ITDs under certain
circumstances to store begin address of the next packet.
•
Load Condition
There are two load conditions for Dword3. The first condition occurs for every TD that
is loaded. Dword3 is loaded when LoadDescriptorDword[3] is asserted. BEPage is
loaded with pci_Data[31:12]. BEOffset is loaded with pci_Data[11:0] +1.
The second condition applies only to an ITD. The end address 1 for an ITD
comes from Offset[RelativeFrame+1] when RelativeFrame is not equal to
FrameCount. When RelativeFrame is odd and not equal to FrameCount,
Offset[RelativeFrame+1] is stored in Offset1. The load condition is
LoadDescriptorDword[5] && RelativeFrame == 1 ||
LoadDescriptorDword[6] && RelativeFrame == 3 ||
LoadDescriptorDword[7] && RelativeFrame == 5 ||
•
Update Condition
There is no update condition for Dword3.
e) Offset0
Offset0 is used exclusively for ITDs. It contains the Offset/PSW Dword of the current
relative frame.
•
Fields
Table 18.11 Offset0 Field Description
Bit Range
Field
31 - 16
Offset0 High
15 - 0
Offset0 Low
If the RelativeFrame is even, Offset[RelativeFrame] is stored in Offset0 Low and
Offset[Relati1] is stored in Offset0 High.
If the RelativeFrame is odd, Offset[RelativeFrame] is stored in Offset0 High and
Offset[Relati1] is stored in Offset1.
•
Load Condition
Offset0 is loaded with the Offset/PSW value of the current RelativeFrame. The
condition is when LoadDescriptorDword[n] is asserted, where n is 4 +
(RelativeFrame / 2).
•
Update Condition
Offset0 is updated when the TD has been serviced (fm_TransactionServiced) and is
being written back to memory (UpdateTD).
The update value is the completion code for the packet and the number of bytes received
on an IN transer or zero for an OUT transfer.
Only the Word containing Offset[RelativeFrame] is updated. The other Word remains
unchanged.
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