Atari ST Disk System Research

2 November 2004

DMA Controller

We have still not yet found the documents for the C025913-38/C398739-001A DMA controller we talked about, so please still send it to us if you can get hold of it. In the meantime we found out how the workings of the chip work through various test programs that indirectly deny or confirm certain operations.


  • How is it attached to bus.
  • What it does.
  • Internal register sizes!
  • Operation.
  • DMA error status register meaning.

Still Unknown

A few bits in status that are not even mentioned anywhere, but obviously related to operation. They are perhaps mirrors of internal bits though.


Tested several WDC1772 features that can be only related to protections. Those possibilites are obviously not discussed in technical documents.

Things like:

  • Exceeding a certain amount/type of data.
  • How exactly reading a whole track works.
  • Any bitmasks used, for example, what happens if the block size says 2^128.