SH7713 datasheet(741/904 Pages) RENESAS

741 / 904 page

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

Rev.1.50 Aug. 30, 2006 Page 701 of 860

REJ09B0288-0150

(b)

Transmit Descriptor 1 (TD1)

TD1 indicates the data length of the transmit buffer used by the corresponding descriptor.

The user should set TD1 before the start of a read by the E-DMAC.

Bit

Bit Name

Initial

Value

R/W

Description

31 to 16

TDL

All 0

R/W

Transmit Buffer Data Length (in bytes)

Indicate the data length of the corresponding transmit

buffer in bytes.

15 to 0



All 0

Reserved

These bits are always read as 0. The write value

should always be 0.

(c)

Transmit Descriptor 2 (TD2)

TD2 indicates the start address of the corresponding 32-bit width transmit buffer. An address

value on a longword boundary should be specified.

The user should set TD2 before the start of a read by the E-DMAC.

(2)

Receive Descriptor

Figure 19.3 shows the relationship between a receive descriptor and receive buffer.

The data of a receive descriptor consists of RD0, RD1, RD2, and padding data in groups of 32 bits

from top to end. The length of padding data is determined according to the descriptor length

specified by the DL0 and DL1 bits in EDMR. In the figure, RBA (bits 31 to 0 in RD2) indicates

the start address of a receive buffer. RBL (bits 31 to 16 in RD1) indicates the usable data length of

the receive buffer. RDL (bits 15 to 0 in RD1) indicates the data length of a received frame.

RD0 indicates whether the receive descriptor is valid or invalid as well as information about

descriptor configuration and status. RD1 indicates the length (storage destination size) of data in

the receive buffer to be received according to the specification of the descriptor. RD2 indicates the

start address of the receive buffer for storing receive data.

Depending on the descriptor specification, one receive descriptor can specify the storing of all

receive data of one frame in a receive buffer (single-frame/single-buffer) or multiple descriptors

can specify the storing of the receive data of one frame in receive buffers (single-frame/multi-

buffer). As an example of single-frame/multi-buffer operation, suppose that a row of multiple

descriptors (descriptor list) is prepared, RBL of each descriptor is 500 bytes, and a 1514-byte

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