SLAU723A October 2017 – October 2018 MSP432E401Y , MSP432E411Y
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 primary control structure copies the next task to the alternate control structure. If the next task is a memory-to-memory transfer, execution starts immediately and runs to completion; if the next task is a peripheral-type transfer, the µDMA waits for a peripheral request to begin.
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.
For an example of operation in Peripheral Scatter-Gather mode, see Figure 8-5 and Figure 8-6. 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 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 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.