Information

Enhanced Three-Speed Ethernet Controllers

MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1

Freescale Semiconductor 16-165

Figure 16-131. Example of eTSEC Memory Structure for BDs

Figure 16-132. Buffer Descriptor Ring

16.6.7.2 Transmit Data Buffer Descriptors (TxBD)

Data is presented to the eTSEC for transmission by arranging it in memory buffers referenced by the

TxBDs. In the TxBD the user initializes the R, PAD, W, I, L, TC, PRE, HFE, CF, and TOE bits and the

length (in bytes) in the first word, and the buffer pointer in the second word. Unused fields or fields written

by the eTSEC must be initialized to zero.

Status & Control

Data Length

Buffer Pointer

Status & Control

Data Length

Buffer Pointer

Rx Buffer Descriptors

Tx Buffer Descriptors

RxBD

Table for Ring n

TxBD

Table for Ring n

TxBD Table

Pointer

RxBD Table

Pointer

(TBASEn)

(RBASEn)

Memory Map

System Memory

Tx Buffer

Rx Buffer

Beginning BD pointer

W = 1