The DMA module is an event-based machine, meaning it requires a peripheral interrupt trigger to start a DMA transfer. Although it can be made into a periodic time-driven machine by configuring a timer as the interrupt trigger source, there is no mechanism within the module itself to start memory transfers periodically.
F2823x/33x DMA用户手册(可根据序列号SPRUFB8D在TI主页查找)开篇第一章Introduction(P8)有上面一段话,很明确地说明了是外设中断触发DMA transfer.