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Software Developer’s Manual 303
Register Descriptions
13.4.27 Receive Descriptor Length
RDLEN (02808h; R/W)
This register determines the number of bytes allocated to the circular receive descriptor buffer. This
value must be 128-byte aligned (the maximum cache line size). Since each descriptor is 16 bytes in
length, the total number of receive descriptors is always a multiple of eight.
Table 13-72. RDLEN Register Bit Description
13.4.28 Receive Descriptor Head
RDH (02810h; R/W)
This register contains the head pointer for the receive descriptor buffer. The register points to a 16-
byte datum. Hardware controls the pointer. The only time that software should write to this register
is after a reset (RCTL.RST or CTRL.RST) and before enabling the receiver function (RCTL.EN).
If software were to write to this register while the receive function was enabled, the on-chip
descriptor buffers can be invalidated and other indeterminate operations might result. Reading the
descriptor head to determine which buffers are finished is not reliable.
Table 13-73. RDH Register Bit Description
31 20 19 7 6 0
Reserved LEN 0
Field Bit(s)
Initial
Value
Description
Zero 6:0 0b
Zero value
Ignore on write. Reads back as 0b.
LEN 19:7 0b
Receive Descriptor length
Provides the number of receive descriptors (in a multiple of eight).
Reserved 31:20 0b
Reserved
Should be written with 0b to ensure future compatibility.
Reads as 0b.
31 16 15 0
Reserved RDH
Field Bit(s)
Initial
Value
Description
RDH 15:0 0b Receive Descriptor Head.
Reserved 31:16 0b
Reserved. Should be written with 0b for future compatibility.
Reads as 0b.