amigappc memory mapping

[Nicolas Bruno BASTIEN <lakomok%free.fr@localhost>]

I was looking at this (in the file src/sys/arch/amigappc/amigappc/machdep.c

---
        /* force memory mapping */
        PPCmem[0].start = 0x8000000;
        PPCmem[0].size  = 0x5f80000;
        PPCmem[1].start = 0x7c00000;
        PPCmem[1].size  = 0x0400000;
---

and I am wondering if this is like this because
amigappc port is experimental (really experimental) or
if there is another reason that I missed ?

And another question:
chip mem does not seam to be included in PPCmem segments, why ?
--
Nicolas Bruno BASTIEN