Datasheet

16-bit Non-PCI Small Form Factor 10/100 Ethernet Controller with Variable Voltage I/O & HP Auto-MDIX Support
Datasheet
Revision 2.9 (03-01-12) 52 SMSC LAN9220
DATASHEET
TX COMMAND ‘A’
Table 3.12 TX Command 'A' Format
BITS DESCRIPTION
31 Interrupt on Completion. When set, the TXDONE flag will be asserted when the current buffer has
been fully loaded into the TX FIFO. This flag may be optionally mapped to a host interrupt.
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 LAN9220 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 31 a Byte offset.
15:14 Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility
13 First Segment (FS). When set, this bit indicates that the associated buffer is the first segment of the
packet.
12 Last Segment. When set, this bit indicates that the associated buffer is the last segment of the
packet
11 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
LAN9220 and used to determine how many extra DWORD’s were added to the end of the Buffer. A
running count is also maintained in the LAN9220 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
0 0 4-byte alignment
0 1 16-byte alignment
1 0 32-byte alignment
11 Reserved