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Old 05 August 2014, 22:48   #11
Toni Wilen
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 43
Posts: 20,660
Originally Posted by phx View Post
I'm not sure why this sequence is required and what SELF_RESET is for. Tests show that clearing P5_AMIGA_RESET is sufficient to reset the system.
Nothing seemed to happen when SELF_RESET was set or cleared.. Lock was unlocked, reading REG_SHADOW shows bit 6 being cleared.

There seems to be no set/clear bit 7 in P5_REG_LOCK (?).
That mysterious bit 0 of REG_LOCK can be set normally (0x81 -> set, 0x01 -> clear). Only bit 0. The one that seems to be very critical.

The other known bit in REG_SHADOW is P5_SHADOW (Bit 0). It may be for mirroring the last 512K of Fast-RAM at 0xfff00000. But after booting in 68k mode the register is 0x4f here, which means SHADOW is inactive? But the mirror at 0xfff00000 is present. So my guess may be wrong.
Bit 0 enables map rom feature. But FFF00000 is always reserved for PPC reset and exception vectors.

Map rom not enabled: FFF00000 is last 512k of fast ram. You can copy KS ROM here and then enable map rom, if you want. Or to last 512k. (BlizKick writes to FFF00000)

Map rom enabled: FFF00000 is second to last 512k of fast ram. last 512k of fast ram is used for kickstart mirror. This is not mirrored in FFFxxxxx anymore.

(I have read all publicly available sources many times already)
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