LAN9250 datasheet(162/421 Pages) MICROCHIP

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LAN9250

DS00001913A-page 162

 2015 Microchip Technology Inc.

11.11.2.1

TX Command ‘A’

TABLE 11-12: 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 device 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 com-

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

used to determine how many extra DWORDs were added to the end of the Buffer. A running count is

also maintained in the device 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.

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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