I gotta believe that between all of the
> OReilly books, and the IEEE papers,and networking magazines, someone out
> there gives a detailed description of the architecture of residential > gateways.
You have something like this..
formatting link
But I'm not sure its at the level you are looking for.
Also, for dial-up modems, there used to be a number of
> enthusiast websites. I haven't seen something similar for DSL modems.
No, nobody dwelves that deep into it any longer. 90% of the DSL router is the same as any other router. Then you have 10% being the DSL chipset in it, which won't get into any gory details unless you read the ADSL tech specs.
Nobody could build their own DSL router from the ground up, there's not much point to anyway.
You could dig around the OpenWRT project support for DSL routers, and there you could probably find data sheets and source code for doing various things.
You'll have hundreds of thousands of lines of code to support an OS and router functions, which is one reason not many would dive into such a thing..