Here is Intersil's datasheet for the ISL3873a, from their own website.
Grab yourself a copy, and follow along as we highlight some good
information that we can use in our source code freely:

http://www.intersil.com/data/fn/fn8015.pdf

Now before we start, I'll admit that this probably isn't exactly the
chip we have in our system, but it is very close, because the Linux
drivers do not seem to care exactly which chip is being used.

First, on page 10, are timing diagrams for the I/O cycles. Further
details are on page 13 and 14. The Buffer Access Path (BAP) is also
discussed in detail on pages 13 and 14. I like to call it the "knot
hole". It is just a way to read and write the memory inside the
chipset, using only a few I/O ports for indirect access. Also, on page
14, dynamic allocation of memory is discussed, and referred to as
"frames" and term "frame ID" (FID) is used.

The datasheet has a lot of other good information, but I'll let you
peruse it at your leisure.

In part 2, we'll look at some Linux device drivers.

William