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Receive Descriptor Field 3 (RDES3)
Table 17-17: Receive Descriptor Field 3 (RDES3)
Description
Bit
Buffer 2 Address Pointer (Next Descriptor Address)
These bits indicate the physical address of Buffer 2 when a descriptor ring structure is used.
If the Second Address Chained (RDES1[24]) bit, in Receive Descriptor Field 1 (RDES1), is
set, this address contains the pointer to the physical memory where the Next descriptor is
present.
If RDES1[24], in Receive Descriptor Field 1 (RDES1), is set, the buffer (Next descriptor)
address pointer must be bus width-aligned (RDES3[1:0] = 0. LSBs are ignored internally.)
However, when RDES1[24], in Receive Descriptor Field 1 (RDES1), is reset, there are no
limitations on the RDES3 value, except for the following condition: The DMA uses the
value programmed in RDES3 [1:0] for its buffer address generation when the RDES3 value
is used to store the start of frame. The DMA ignores RDES3 [1:0] if the address pointer is
to a buffer where the middle or last part of the frame is stored.
31:0
Related Information
Receive Descriptor Field 1 (RDES1)
on page 17-46
Receive Descriptor Field 4 (RDES4)
The extended status is written only when there is status related to IPC or timestamp available. The availability
of extended status is indicated by Bit 0 in RDES0. This status is available only when the Advance Timestamp
or IPC Full Offload feature is selected.
Table 17-18: Receive Descriptor Field 4 (RDES4)
Description
Bit
Reserved
†
31:28
Layer 3 and Layer 4 Filter Number Matched
These bits indicate the number of the Layer 3 and Layer 4 Filter that matched the received
frame.
• 00: Filter 0
• 01: Filter 1
• 10: Filter 2
• 11: Filter 3
This field is valid only when Bit 24 or Bit 25 is set high. When more than one filter matches,
these bits give only the lowest filter number.
†
27:26
Ethernet Media Access Controller
Altera Corporation
cv_54017
Receive Descriptor Field 3 (RDES3)
17-48
2013.12.30