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Figure 17-8: TX DMA Operation in OSF Mode
Error?
yes
no
Own Bit Set?
yes
no
(Re-)Fetch Next
Descriptor
Start
Tx DMA
Transfer Data
from Buffer(s)
Error?
yes
no
Frame
Transfer
Complete?
no
Timestamp
Present?
yes
no
Write Status Word to
Previous Frame’s TDES0
Error?
no
yes
Write Timestamp
to TDES2 & TDES3
for Previous Frame
Error?
yes
no
Stop
Rx DMA
Start
Timestamp
Present?
yes
no
Tx DMA
Suspended
Write Timestamp to RDES2 &
TDES3 for Previous Frame
Poll Demand
yes
Wait for Previous
Frame’s TX Status
Second
Frame?
yes
no
Close Intermediate
Descriptor
Error?
no
Error?
no
Write Status Word to
Previous Frame’s TDES0
Previous Frame
Status Available
yes
yes
Transmit Frame Processing
The transmit DMA expects that the data buffers contain complete Ethernet frames, excluding preamble,
pad bytes, and FCS fields. The DA, SA, and Type/Len fields 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 Descriptor
(TDES1[29]) and the Last Descriptor (TDES1[30]), respectively. †
Ethernet Media Access Controller
Altera Corporation
cv_54017
Transmit Frame Processing
17-30
2013.12.30