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Annotation of Net2/arch/amiga/amiga-mmu, revision 1.1.1.1

1.1       root        1: The HP300 version uses a kernel which is loaded into the range 0xfffxxx... but
                      2: is linked for range 0x000.. This causes the problem that with switching the
                      3: MMU to the mapped kernel, the PC becomes invalid. The HP version solves the
                      4: problem by mapping 1:1 the last page of physical memory into virtual memory.
                      5: 
                      6: On the Amiga, there *is* memory at PA 0x0, so we might as well use it, causes
                      7: much less grief and weirdness in locore.s. However, since memory down there
                      8: is CHIPMEM, inherently slower than FASTMEM, and badly needed for framebuffer
                      9: storage space, we'll copy the kernel over to the first bank of FASTRAM, and
                     10: when enabling the MMU, the kernel will execute in FASTRAM, although the PC
                     11: stays the same.
                     12: 
                     13: This strategy has the big advantage (compared to the solution in Amiga MACH)
                     14: that we can link the kernel absolutely to VA 0, for all memory models, since
                     15: we'll never execute the kernel in the FASTMEM space while the MMU is turned
                     16: off.
                     17: 
                     18: This strategy also means, that we don't have to relocate any addresses while
                     19: bootstrapping the mmu!!
                     20: 
                     21: Initialization of the MMU happens in amiga_init.c. This file is quite a mess,
                     22: I have generated it trying to understand what's happening in the hp300 locore.s
                     23: file. I think, it should be able to handle MMU initialization much cleaner
                     24: now that we don't have to think about relocation until the MMU is enabled.
                     25: If you need your daily bit of horror, take a look at amiga_init.c...

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