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 μDMA request. Upon detecting a request from the peripheral,
the μDMA controller uses the primary control structure to copy one entry from the list to the alternate
control structure and then performs the transfer. At the end of this transfer, the next transfer is started
only if the peripheral again asserts a μDMA request. The μDMA controller continues to perform
transfers from the list only when the peripheral is making a request, until the last transfer is complete.
A completion interrupt is generated only after the last transfer.
By using this method, the μDMA controller can transfer data 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 360 and Figure 8-6 on page 361, 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 is copied to a single peripheral data register. Figure 8-5 on page 360
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 is used for the operation is configured to copy from the task list to the
alternate control structure.
Figure 8-6 on page 361 shows the sequence as the µDMA controller performs 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 performs 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.
359July 24, 2012
Texas Instruments-Production Data
Stellaris
®
LM3S6G65 Microcontroller
OBSOLETE: TI has discontinued production of this device.
