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Transmit Control Register - TCTL (00400h; R/W) — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 363
14.3.64 Transmit Control Register - TCTL (00400h; R/
W)
This register controls all transmit functions for the 82575.
Software can choose to abort packet transmission in less than the Ethernet mandated 16 collisions. For
this reason, hardware provides CT.
Note: While 802.3x flow control is only defined during full duplex operation, the sending of PAUSE
frames via the SWXOFF bit is not gated by the duplex settings within the 82575. Software
should not write a 1b to this bit while the 82575 is configured for half-duplex operation.
RTLC configures the 82575 to perform retransmission of packets when a late collision is detected. Note
that the collision window is speed dependent: 64 bytes for 10/100 Mb/s and
512 bytes for 1000 Mb/s operation. If a late collision is detected when this bit is disabled, the transmit
function assumes the packet has successfully transmitted. This bit is ignored in full-duplex mode.
IPFRSP_DIS 14 0b IP Fragment Split Disable
When this bit is set the header of IP fragmented packets are not set.
Reserved 15 0b Reserved
Reserved 17:16 00b Reserved
Must be set to 00b.
LEF 18 0b Forward Length Error Packets
If set, packets with length error are forwarded to the host. Otherwise, are dropped.
Reserved 31:19 00h Reserved
Should be written with 0b to ensure future capability.
Field Bit(s)
Initial
Value
Description
Reserved 0 0b Reserved
Write as 0b for future compatibility.
EN 1 0b Transmit Enable
The transmitter is enabled when this bit is set to 1b. Writing 0b to this bit stops
transmission after any in progress packets are sent. Data remains in the transmit FIFO
until the device is re-enabled. Software should combine this operation with reset if the
packets in the TX FIFO should be flushed.
Reserved 2 0b Reserved
Reads as 0b.
Should be written to 0b for future compatibility.
PSP 3 0b Pad Short Packets
0b = Do not pad.
1b = Pad.
Padding makes the packet 64 bytes long. This is not the same as the minimum
collision distance.
If padding of short packets is allowed, the value in the Tx descriptor length field
should be not less than 17 bytes.