SH7672 datasheet(460/1292 Pages) RENESAS

460 / 1292 page

Section 12 Ethernet Controller (EtherC)

Rev. 1.00 Nov. 14, 2007 Page 434 of 1262

REJ09B0437-0100

12.4.6

Operation by IPG Setting

The EtherC has a function to change the non-transmission period IPG (Inter Packet Gap) between

transmit frames. By changing the set values of the IPG setting register (IPGR), the transmission

efficiency can be raised and lowered from the standard value. IPG settings are prescribed in

IEEE802.3 standards. When changing settings, adequately check that the respective devices can

operate smoothly on the same network.

IPG*

[1]

[2]

[3]

[4]

[1]

[2]

[3]

[4]

[5]

......

Packet

Note: * IPG may be longer than the set value, depending on the state of the circuit and the system bus.

Case A

(short IPG)

Case B

(long IPG)

Figure 12.7 Changing IPG and Transmission Efficiency

12.4.7

Flow Control

The EtherC supports flow control functions conforming to IEEE802.3x in full-duplex operations.

Flow control can be applied to both receive and transmit operations. The methods for transmitting

PAUSE frames when controlling flow are as follows:

Automatic PAUSE Frame Transmission: For receive frames, PAUSE frames are automatically

transmitted when the number of data in the receive FIFO (included in E-DMAC) reaches the value

set in the flow control FIFO threshold register (FCFTR) of the E-DMAC. The TIME parameter

included in the PAUSE frame at this time is set by the automatic PAUSE frame setting register

(APR). The automatic PAUSE frame transmission is repeated until the number of data in the

receive FIFO becomes less than the FCFTR setting as the receive data is read from the FIFO.

The upper limit of the number of retransfers of the PAUSE frame can also be set by the automatic

PAUSE frame retransfer count set register (TPAUSER). In this case, PAUSE frame transmission

is repeated until the number of data becomes FCFTR value set or below, or the number of

transmits reaches the value set by TPAUSER. The automatic PAUSE frame transmission is

enabled when the TXF bit in the EtherC mode register (ECMR) is 1.

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