Have you tried the RKM: Devices 3ยบ Ed., or the "Amiga Hardware Reference Manual" book?
If you dig up for Amiga assembly sites I bet you can get lucky.
P.S. In the RKM: Libraries, in the Preface the following is written:
"The Amiga ROM Kernel Reference Manual: Devices is a companion book to this volume detailing how to write code for the Amiga'a lower level I/O hardware.
... and the Amiga Hardware Reference Manual, an in-depth description of the custom chips and other hardware components underlying the Amiga's sophisticated design." They must be of some help.
Or if you are a adventurous type of person, you can just reverse-engineer the AmigaOS to know how its guts work. Imagen it as breaking into the cemetary at the midle of the night and snatch a corpse for scientific/medical researche (big laugh).