Posted on November 10, 2016 at 16:21Dmitry,
Just to make this a bit clearer as it may be surprising for those who are accustomed to peripherals with fixed set of control registers - this is a concept in the more complex peripherals which have their own DMA - often some of the control data does not sit in registers in the register area, but in some part of main memory (maybe addressed by a ''fixed'' register), from where the module picks it at the beginning of an action and returns modification at the end of the action. This makes even more sense if the device acts on a set of buffers (here, containing of a combination of memory-based-controls and the actual data) in the memory - if some of the ''memory-based-controls'' is a ''next-block'' pointer, then these blocks can be chained and there is no limit on their number.
The downside is that the peripheral gets more complex and its operation may take more time as it needs to pick the control-words from memory (shared with processor and other peripherals) prior it starts the action; so you will find this sort of ''machine'' only on complex peripherals with a great deal of ''autonomy'' such as ETH and USB.
JW
