According to page 1158 of Vybrid Reference Manual (F-Series; VYBRIDRM Rev 7, 06/2014), memory range from 0x20000000 to 0x2FFFFFFF is QuadSPI0 and "cacheable write-back".
My question is: "write-back" to what? Probably not to flash. Can we put some ferromagnetic memory in there and work with it just like with normal memory, but non-volatile? Where do I read more about this kind of setup? Are there any examples?
Or is does this mean something else?