Hi Sue,
These kind of DMA is used mainly in Audio applications. The purpose of scatter/gather DMA is the transfer of data from/to non-contiguous memory blocks. Whereas the Delay line DMA is used to support reads and writes to external delay line buffers with limited core interaction. In this sense, delay line DMA is basically a quantity of integrated writes followed by reads from external memory-called a delay line DMA access. We have an application note which talks about how to implement Delay Lines on SHARC Processors. I guess, knowing more about delay lines will answer your query. Please have a look into this application note.
http://www.analog.com/static/imported-files/application_notes/EE_295_SHARC_Rev_1.pdf
Thanks & Regards
Jithul
