经过一番挖掘后，我对DMA的理解正在追随 -
1）总线主控DMA控制器驻留在设备卡上。
a) does cycle stealing, and takes control of system bus to control transfers. Plz correct.
b) hard-disk controllers and NIC are examples
c) I know of BR and BG signals used to take control of system bus to access memory
2）第三方DMA，留在系统板上。
a) performs burst mode transfers (i am not very firm on this though)
b) uses channels as scatter-gather lists for transfers
c) do not know which devices use them. please help.
d) have no idea on how the DMA accesses memory in this case.
我想了解的另一个重要项目是 - 让设备制造商选择1）或2）之一的要求是什么。 如果我提到的理解是正确的，请告诉我。