LAN9117_08 Datasheet, PDF(49/136 Page) SMSC Corporation – High Performance Single-Chip 10/100 Non-PCI Ethernet Controller

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LAN9117_08 Datasheet, PDF (49/136 Pages) SMSC Corporation – High Performance Single-Chip 10/100 Non-PCI Ethernet Controller

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High Performance Single-Chip 10/100 Non-PCI Ethernet Controller

Datasheet

3.13.1

TX Buffer Format

TX buffers exist in the hostâs memory in a given format. The host writes a TX command word into the

TX data buffer before moving the Ethernet packet data. The TX command A and command B are 32-

bit values that are used by the LAN9117 in the handling and processing of the associated Ethernet

packet data buffer. Buffer alignment, segmentation and other packet processing parameters are

included in the command structure. The following diagram illustrates the buffer format.

Host Write

Order 31

1st

TX Command 'A'

2nd

TX Command 'B'

3rd

Optional offset DWORD0

Optional offset DWORDn

Offset + Data DWORD0

Last Data & PAD

Optional Pad DWORD0

Last

Optional Pad DWORDn

Figure 3.14 TX Buffer Format

Figure 3.14, "TX Buffer Format", shows the TX Buffer as it is written into the LAN9117. It should be

noted that not all of the data shown in this diagram is actually stored in the TX data FIFO. This must

be taken into account when calculating the actual TX data FIFO usage. Please refer to Section 3.13.5,

"Calculating Actual TX Data FIFO Usage," on page 53 for a detailed explanation on calculating the

actual TX data FIFO usage.

Note 3.15 The LAN9117 host bus interface supports 16-bit bus transfers; internally, all data paths are

32-bits wide. Figure 3.14 describes the host write ordering for pairs of atomic 16-bit

transactions.

3.13.2 TX Command Format

The TX command instructs the TX FIFO controller on handling the subsequent buffer. The command

precedes the data to be transmitted. The TX command is divided into two, 32-bit words; TX command

âAâ and TX command âBâ.

There is a 16-bit packet tag in the TX command âBâ command word. Packet tags may, if host software

desires, be unique for each packet (i.e., an incrementing count). The value of the tag will be returned

SMSC LAN9117

DATASHEET

Revision 1.5 (07-11-08)

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