No
Yes
No
Error Condition?
OWN bit
set?
Error
Condition?
Error
Condition?
Error
Condition?
Start
Start Tx DMA
Stop Tx DMA
A
(Re-)fetch next descriptor
Yes
No
Tx DMA suspended
N
o
Pe
n
d
in
g
st
a
tu
s
a
n
d
St
a
rt
=
0
A
Poll demand
No
Transfer data from
buffer(s)
Yes
Frame xfer
complete?
Timestamp
present?
No
Yes
Write timestamp to
TDES6 and TDES7
Write status word to
prev.
IUDPH¶V 7'(6
0
No
Yes
Yes
Close intermediate
decriptor
No
Second
frame?
No
Yes
Yes
:DLW IRU SUHYLRXV IUDPH¶V
TX status
Pervious
frame status
avaliable
Timestamp
present?
Yes
Write timestamp to
TDES6 and TDES7
for previous frame
Error
condition?
No
Yes
No
Write status word to
SUHY IUDPH¶V 7'(6
0
Error
condition?
No
Yes
Functional Description
904
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Ethernet Controller
Figure 15-8. TX DMA OSF Mode Operation Using Descriptors
15.3.3.6.3 Transmit Frame Processing
The TX DMA expects that the data buffers contain complete Ethernet frames, excluding preamble, pad
bytes, and Frame Check Sequence (FCS) fields. The Destination Address (DA), Source Address (SA),
and Type/Length fields must contain valid data. If the Transmit Descriptor indicates that the MAC must
disable CRC or PAD insertion, the buffer must have complete Ethernet frames (excluding preamble),
including the CRC bytes. Frames can be data-chained and can span several buffers. Frames must be
delimited by the First Segment Descriptor and the Last Segment Descriptor, respectively. The First
Descriptor bit is located at TDES0[28] and the Last Descriptor is located at TDES0[29].