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Software Developer’s Manual 325
Register Descriptions
13.4.47 Receive Checksum Control
RXCSUM (05000h; R/W)
The Receive Checksum Control register controls the receive checksum offloading features of the
Ethernet controller. The Ethernet controller supports the offloading of three receive checksum
calculations: the Packet Checksum, the IP Header Checksum, and the TCP/UDP Checksum.
The frame types that are supported:
• Ethernet II
• Ethernet SNAP
Table 13-88. RXCSUM Register Bit Description
WTHRESH 21:16 1b
Write Back Threshold
WTHRESH controls the write back of processed receive
descriptors. This threshold refers to the number of receive
descriptors in the Ethernet controller’s on-chip buffer which are
ready to be written back to host memory. In the absence of
external events (explicit flushes), the write back occurs only after
more than WTHRESH descriptors are available for write back.
WTHRESH must contain a non-zero value to take advantage of
the write back bursting capabilities of the Ethernet controller.
A value of 1b causes the descriptors to be written back as soon
as one cache line is available. A value of WTHRESH can be in
either cache line units, or based on number of descriptors based
on RXDCTL.GRAN.
RSV 23:22 0b
Reserved
Reads as 0b.
Should be written as 0b for future compatibility.
GRAN 24 1b
Granularity
Set the values of PTHRESH, HTHRESH and WTHRESH in units
of cache lines or descriptors (each descriptor is 16 bytes)
0b = Cache line granularity.
1b = Descriptor granularity.
Reserved 31:25 0b
Reserved
Reads as 0b.
Should be written as 0b for future compatibility.
Field Bit(s)
Initial
Value
Description
31:11 10 9 8 7 0
RSV IPV6OFL
1
1. Not applicable to the 82544GC/EI.
TUOFLD IPOFLD PCSS