Altera cyclone V Technical Reference page 1236

cv_5v4
2016.10.28
Figure 17-6: TX DMA Operation in Default Mode
TX DMA Operation: OSF Mode
While in the Run state, the transmit process can simultaneously acquire two frames without closing the
Status descriptor of the first [if Bit 2 (OSF) in Register 6 (Operation Mode Register) is set]. As the transmit
process finishes transferring the first frame, it immediately polls the transmit descriptor list for the second
frame. If the second frame is valid, the transmit process transfers this frame before writing the first frame's
status information.
Ethernet Media Access Controller
Send Feedback
Start
Tx DMA
(Re-)Fetch Next
Descriptor
Error?
Poll Demand
no
Tx DMA
Own Bit Set?
Suspended
Transfer Data
from Buffer(s)
Error?
Frame
no
Transfer
Complete?
Wait for
Tx Status
Close Intermediate
Descriptor
Timestamp
Present?
Write Status
Word to TDES0
no
Error?
†
TX DMA Operation: OSF Mode
Start
Stop
Tx DMA
yes
no
yes
yes
no
yes
yes
Write Timestamp
to RDES2 & RDES3
no
no
Error?
yes
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