UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
752 of 1269
NXP Semiconductors
UM10503
Chapter 26: LPC43xx Ethernet
Fig 76. Transmit descriptor fetch (read)
O
W
N
Reserved for
Status [3:0]
Buffer 1 Address [31:0]
Buffer 2 Address [31:0] or Next Descriptor Address [31:0]
R
E
S
Buffer 2 Byte Count [28:16]
Buffer 1 Byte Count [12:0]
31
0
TDES0
TDES3
TDES2
TDES1
R
E
S
R
E
S
Ctrl
[30:26]
T
T
S
E
R
E
S
Ctrl
[23:20]
Reserved for
Status [17:7]
SLOT
Number
[6:3]
Table 584. Transmit descriptor word 0 (TDES0)
Bit
Symbol
Description
0
DB
Deferred Bit
When set, this bit indicates that the MAC defers before transmission because of the presence of
carrier. This bit is valid only in Half-Duplex mode.
1
UF
Underflow Error
When set, this bit indicates that the MAC aborted the frame because data arrived late from the Host
memory. Underflow Error indicates that the DMA encountered an empty transmit buffer while
transmitting the frame. The transmission process enters the Suspended state and sets both
Transmit Underflow (Register 5[5]) and Transmit Interrupt (Register 5[0]).
2
ED
Excessive Deferral
When set, this bit indicates that the transmission has ended because of excessive deferral of over
24,288 bit times (155,680 bits times in 1,000-Mbps mode or if Jumbo Frame is enabled) if the
Deferral Check (DC) bit in the MAC Control register is set high.
6:3
CC/
SLOTNUM
CC: Collision Count (Status field)
These status bits indicate the number of collisions that occurred before the frame was transmitted.
This count is not valid when the Excessive Collisions bit (TDES0[8]) is set. The core updates this
status field only in the half-duplex mode.
SLOTNUM: Slot Number Control Bits in AV Mode
These bits indicate the slot interval in which the data should be fetched from the corresponding
buffers addressed by TDES2 or TDES3. When the transmit descriptor is fetched, the DMA
compares the slot number value in this field with the slot interval maintained in the core . It fetches
the data from the buffers only if there is a match in values. These bits are valid only for the AV
channels (not channel 0).
7
VF
VLAN Frame
When set, this bit indicates that the transmitted frame was a VLAN-type frame.