AlecV, you are right about initialize routine, one inside ROM is quite small, and do just init of floppy and for example in 1715 it first copy itself in RAM.
About banked memory, good thing is that on Zanders site, that I gave link, there is a dump of CS (chip-select) PROM so that should at least help some things, but there is no schematics of 1715W, will continue my work on ROM disassembly also will take track 0 and disassemble that code to see how some things are done.
Think that ther is no actual DMA chip (at least in 1715 version).
Thanks for link