Datasheet

Section 21 Ethernet Controller Direct Memory Access Controller (E-DMAC)
Rev. 2.00 Aug. 20, 2008 Page 820 of 1198
REJ09B0403-0200
(2) Receive Descriptor
Figure 21.3 shows the relationship between a receive descriptor and the receive buffer. In frame
reception, the E-DMAC performs data rewriting up to a receive buffer 16-byte boundary,
regardless of the receive frame length. Finally, the actual receive frame length is reported in the
lower 16 bits of RD1 in the descriptor. Data transfer to the receive buffer is performed
automatically by the E-DMAC to give a one frame/one buffer or one frame/multi-buffer
configuration according to the size of one received frame.
Receive descriptor Receive buffer
Valid receive data
R
A
C
T
R
D
L
E
R
F
P
1
R
F
E
RFS26 to RFS0RD0
RBL
H'0
RDL
RD1
RBA
Padding (4 bytes)
RD2
R
F
P
0
31 30 29 28 27 26 0
31 20 19 16
31 0
15 0
Figure 21.3 Relationship between Receive Descriptor and Receive Buffer