HD6417618 datasheet(323/646 Pages) RENESAS

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Section 12 Ethernet Controller Direct Memory Access Controller (E-DMAC)

Rev. 6.00 Jun. 12, 2007 Page 291 of 610

REJ09B0131-0600

(b)

Receive Descriptor 1 (RD1)

RD1 specifies the receive buffer length (maximum 64 kbytes).

Bit

Bit Name

Initial

value

R/W

Description

31 to 16

RBL

All 0

R/W

Receive Buffer Length

These bits specify the maximum reception byte length

in the corresponding receive buffer.

The transfer byte length must align with a 16-byte

boundary (bits 19 to 16 cleared to 0). The maximum

receive frame length with one frame per buffer is

1,514 bytes, excluding the CRC data. Therefore, for

the receive buffer length specification, a value of

1,520 bytes (H'05F0) that takes account of a 16-byte

boundary is set as the maximum receive frame

length.

15 to 0

RDL

All 0

R/W

Receive Data Length

These bits specify the data length of a receive frame

stored in the receive buffer.

The receive data transferred to the receive buffer

does not include the 4-byte CRC data at the end of

the frame. The receive frame length is reported as the

number of words (valid data bytes) not including this

CRC data.

(c)

Receive Descriptor 2 (RD2)

RD2 specifies the 32-bit receive buffer start address. The receive buffer start address must be

aligned with a longword boundary. However, when SDRAM is connected, it must be aligned with

a 16-byte boundary.

12.3.2

Transmission

When the transmit function is enabled and the transmit request bit (TR) is set in the E-DMAC

transmit request register (EDTRR), the E-DMAC reads the descriptor used last time from the

transmit descriptor list (in the initial state, the descriptor indicated by the transmission descriptor

start address register (TDLAR)). If the setting of the TACT bit in the read descriptor is active, the

E-DMAC reads transmit frame data sequentially from the transmit buffer start address specified

by TD2, and transfers it to the EtherC. The EtherC creates a transmit frame and starts transmission

to the MII. After DMA transfer of data equivalent to the buffer length specified in the descriptor,

the following processing is carried out according to the TFP value.

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