SH7713 datasheet(742/904 Pages) RENESAS

742 / 904 page

Section 19 Ethernet Controller Direct Memory Access Controller (E-DMAC)

Rev.1.50 Aug. 30, 2006 Page 702 of 860

REJ09B0288-0150

Ethernet frame is received. In such a case, the received Ethernet frame is transferred sequentially

to buffers, 500 bytes for each buffer, starting with the first descriptor. Only the last 14 bytes are

transferred to the fourth buffer. When a frame longer than RBL of a descriptor is received, the

E-DMAC transfers the remaining data to the receive buffer by using the subsequent descriptors.

As an example of efficient single-frame/multi-buffer operation, information items on different

processing layers in an Ethernet frame can be separated from each other by using different buffers.

For example, the destination address, transmit source address, and type field data in an Ethernet

frame can be stored in buffer 1 (with RBL set to 14 bytes) and the remaining data can be stored in

buffer 2 (with RBL set to 1500 bytes). All receive frames, of course, can be stored in a single

buffer if multiple descriptors are prepared and RBL of each descriptor is set to more than 1514

bytes (maximum Ethernet frame length).

Receive descriptor

Receive buffer

Valid receive data

RFS26 to RFS0

RD0

RBL

RDL

RD1

RBA

Padding (4/20/52 bytes)*

RD2

31 30 29 28 27 26

Note: * According to the descriptor length set by the DL0 and DL1 bits in EDMR, the padding size is determined as follows:

For 16 bytes: Padding = 4 bytes

For 32 bytes: Padding = 20 bytes

For 64 bytes: Padding = 52 bytes

Figure 19.3 Relationship between Receive Descriptor and Receive Buffer

SH7713 Datasheet(PDF) 742 Page - Renesas Technology Corp