LAN9312 datasheet(125/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

SMSC LAN9312

125

Revision 1.2 (04-08-08)

DATASHEET

Both TX command ‘A’ and TX command ‘B’ are required for each buffer in a given packet. TX

command ‘B’ must be identical for every buffer in a given packet. If the TX command ‘B’ words do not

match, the Ethernet controller will assert the Transmitter Error (TXE) flag.

9.8.2.1

TX Command ‘A’

Table 9.10 TX Command 'A' Format

BITS

DESCRIPTION

Interrupt on Completion (IOC).

When set, the TX_IOC bit will be asserted in the Interrupt Status

30:26

Reserved.

These bits are reserved. Always write zeros to this field to guarantee future compatibility.

25:24

Buffer End Alignment.

This field specifies the alignment that must be maintained on the last data

transfer of a buffer. The host will add extra DWORDs of data up to the alignment specified in the

table below. The LAN9312 will remove the extra DWORDs. This mechanism can be used to maintain

cache line alignment on host processors.

23:21

Reserved.

These bits are reserved. Always write zeros to this field to guarantee future compatibility

20:16

Data Start Offset (bytes).

This field specifies the offset of the first byte of TX data. The offset value

can be anywhere from 0 bytes to a 31 byte offset.

15:14

Reserved.

These bits are reserved. Always write zeros to this field to guarantee future compatibility

First Segment (FS).

When set, this bit indicates that the associated buffer is the first segment of the

packet.

Last Segment.

When set, this bit indicates that the associated buffer is the last segment of the

packet

Reserved.

These bits are reserved. Always write zeros to this field to guarantee future compatibility.

10:0

Buffer Size (bytes).

This field indicates the number of bytes contained in the buffer following this

command. This value, along with the Buffer End Alignment field, is read and checked by the

LAN9312 and used to determine how many extra DWORDs were added to the end of the Buffer. A

running count is also maintained in the LAN9312 of the cumulative buffer sizes for a given packet.

This cumulative value is compared against the Packet Length field in the TX command ‘B’ word and

if they do not correlate, the TXE flag is set.

Note:

The buffer size specified does not include the buffer end alignment padding or data start

offset added to a buffer.

[25]

[24]

End Alignment

4-byte alignment

16-byte alignment

32-byte alignment

Reserved

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