Description
Bit
EC: Excessive Collision
When set, this bit indicates that the transmission was aborted after 16 successive collisions
while attempting to transmit the current frame. If Bit 9 (Disable Retry) bit in the Register
0 (MAC Configuration Register) is set, this bit is set after the first collision, and the
transmission of the frame is aborted.
†
8
VF: VLAN Frame
When set, this bit indicates that the transmitted frame is a VLAN-type frame.
†
7
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 EMAC updates this status field only in the half-duplex mode.
6:3
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 Bit 4 (Deferral Check) bit in Register 0 (MAC Configuration Register) is set
high.
†
2
UF: Underflow Error
When set, this bit indicates that the MAC aborted the frame because the 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]).
†
1
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 the half-duplex mode.
†
0
Table 17-9: Transmit Descriptor Word 1 (TDES1)
Description
Bit
Reserved
31:29
TBS2: Transmit Buffer 2 Size
This field indicates the second data buffer size in bytes. This field is not valid if TDES0[20]
is set.
†
28:16
Reserved
†
15:13
TBS1: Transmit Buffer 1 Size
These bits indicate the first data buffer byte size, in bytes. If this field is 0, the DMA ignores
this buffer and uses Buffer 2 or the next descriptor, depending on the value of TCH
(TDES0[20]).
†
12:0
Altera Corporation
Ethernet Media Access Controller
17-41
Transmit Descriptor
cv_54017
2013.12.30