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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
884 of 1441
NXP Semiconductors
UM10503
Chapter 28: LPC43xx/LPC43Sxx Ethernet
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.
In OSF mode, the Run state Transmit DMA operates in the following sequence:
1. The DMA operates as described in steps 1 to 6 of the TxDMA (default mode).
2. Without closing the previous frame’s last descriptor, the DMA fetches the next
descriptor.
3. If the DMA owns the acquired descriptor, the DMA decodes the transmit buffer
address in this descriptor. If the DMA does not own the descriptor, the DMA goes into
Suspend mode and skips to Step 7.
4. The DMA fetches the Transmit frame from the Host memory and transfers the frame
to the MTL until the End-of-Frame data is transferred, closing the intermediate
descriptors if this frame is split across multiple descriptors.
5. The DMA waits for the previous frame’s frame transmission status and
Time stamp
.
Once the status is available, the DMA writes the
Time stamp
to TDES2 and TDES3, if
such
Time stamp
was captured (as indicated by a status bit). The DMA then writes the
status, with a cleared Own bit, to the corresponding TDES0, thus closing the
descriptor. If
Time stamp
ing was not enabled for the previous frame, the DMA does not
alter the contents of TDES2 and TDES3.
6. If enabled, the Transmit interrupt is set, the DMA fetches the next descriptor, then
proceeds to Step 3 (when Status is normal). If the previous transmission status shows
an underflow error, the DMA goes into Suspend mode (Step 7).
7. In Suspend mode, if a pending status and
Time stamp
are received from the MTL, the
DMA writes the
Time stamp
(if enabled for the current frame) to TDES2 and TDES3,
then writes the status to the corresponding TDES0. It then sets relevant interrupts and
returns to Suspend mode.
8. The DMA can exit Suspend mode and enter the Run state (go to Step 1 or Step 2
depending on pending status) only after receiving a Transmit Poll demand (DMA
Transmit Poll Demand register).
Remark:
As the DMA fetches the next descriptor in advance before closing the current
descriptor, the descriptor chain should have more than 2 different descriptors for correct
and proper operation.
The basic flow is described in
.