LAN9500 Datasheet, PDF (48/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
TABLE 5-41: TX COMMAND A FORMAT
BITS
31:18
17:16
15:14
13
12
11
10:0
DESCRIPTION
RESERVED
Data Start Offset (bytes)
This field specifies the offset of the first byte of TX Data. The offset value ranges between 0 bytes
and 3 bytes.
RESERVED
First Segment
When set, this bit indicates that the associated buffer is the first segment of the frame.
Last Segment
When set, this bit indicates that the associated buffer is the last segment of the frame.
RESERVED
Buffer Size (bytes)
This field indicates the number of bytes contained in the buffer following the two command DWORDS
(TX Command A and TX Command B). This value, along with the Data Start Offset field, is used by
the FCT to determine how many extra bytes were added to the end of the Buffer. A running count is
also maintained in the FCT of the cumulative buffer sizes for a given frame. This cumulative value is
compared against the Frame 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 bytes added due to the end of buffer alignment padding or
the Data Start Offset field.
TABLE 5-42: TX COMMAND B FORMAT
BITS
DESCRIPTION
31:15
14
13
12
11
10:0
RESERVED
TX Checksum Enable (CK)
If this bit is set in conjunction with the first segment bit (FS) in TX Command 'A' and the TX checksum
offload engine enable bit (TXCOE_EN) in the checksum offload engine control register (COE_CR),
the TX checksum offload engine (TXCOE) will calculate an L3 checksum for the associated frame.
Note: This bit only needs to be set for the first buffer of a frame.
Add CRC Disable
When set, the automatic addition of the CRC is disabled.
Disable Ethernet Frame Padding
When set, this bit prevents the automatic addition of padding to an Ethernet frame of less than 64
bytes. The CRC field is also added despite the state of the Add CRC Disable field.
RESERVED
Frame Length (bytes)
This field indicates the total number of bytes in the current frame. This length does not include the
offset or padding. If the Frame Length field does not match the actual number of bytes in the frame,
the Transmitter Error (TXE) flag will be set (in the Interrupt Status Register (INT_STS) and the
interrupt endpoint). This value is read by the TX FIFO controller, and is used to determine the amount
of data that must be moved from the TX data FIFO into the TLI block. If the byte count is not aligned
to a DWORD boundary, the TX FIFO Controller will issue the correct byte enables to the TLI layer
during the last write. Invalid bytes in the last DWORD will not be passed to the TLI for transmission.
DS00001875A-page 48
 2010 - 2015 Microchip Technology Inc.