High Performance Single-Chip 10/100 Non-PCI Ethernet Controller
Datasheet
There is a 16-bit packet tag in the TX command ‘B’ 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
in the RX status word for the associated packet. The Packet tag can be used by host software to
uniquely identify each status word as it is returned to the host.
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.
TX COMMAND ‘A’
Table 3.11 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
25:24
Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility.
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 LAN9117 will remove the extra DWORDs. This mechanism can be used to maintain
cache line alignment on host processors.
[25]
0
[24]
0
End Alignment
4-byte alignment
16-byte alignment
32-byte alignment
Reserved
0
1
1
0
1
1
23:21
20:16
Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility
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
13
Reserved. These bits are reserved. Always write zeros to this field to guarantee future compatibility
First Segment. 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 LAN9117
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 LAN9117 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.
SMSC LAN9117
Revision 1.1 (05-17-05)
DATA4S9HEET
SMSC [ SMSC CORPORATION ]
