LM3S1776 Datasheet, PDF (295/735 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Stellaris® LM3S1776 Microcontroller
8.2.6.6
Peripheral Scatter-Gather
Peripheral Scatter-Gather mode is very similar to Memory Scatter-Gather, except that the transfers
are controlled by a peripheral making a DMA request. Upon detecting a DMA request from the
peripheral, the μDMA controller will use the primary control structure to copy one entry from the list
to the alternate control structure, and then perform the transfer. At the end of this transfer, the next
transfer will only be started if the peripheral again asserts a DMA request. The μDMA controller will
continue to perform transfers from the list only when the peripheral is making a request, until the
last transfer is complete. A completion interrupt will only be generated after the last transfer.
By programming the μDMA controller using this method, data can be transferred to or from a
peripheral from a set of arbitrary locations whenever the peripheral is ready to transfer data.
Refer to Figure 8-5 on page 296 and Figure 8-6 on page 297, which show an example of operation
in Peripheral Scatter-Gather mode. This example shows a gather operation, where data from three
separate buffers in memory will be copied to a single peripheral data register. Figure 8-5 on page 296
shows how the application sets up a µDMA task list in memory that is used by the controller to
perform three sets of copy operations from different locations in memory. The primary control
structure for the channel that will be used for the operation is configured to copy from the task list
to the alternate control structure.
Figure 8-6 on page 297 shows the sequence as the µDMA controller peforms the three sets of copy
operations. First, using the primary control structure, the µDMA controller loads the alternate control
structure with task A. It then peforms the copy operation specified by task A, copying the data from
the source buffer A to the peripheral data register. Next, the µDMA controller again uses the primary
control structure to load task B into the alternate control structure, and then performs the B operation
with the alternate control structure. The process is repeated for task C.
November 17, 2011
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