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Understand NK entry point better

This commit is contained in:
DBJ314 2018-04-22 14:06:38 -04:00 committed by Elliot Nunn
parent 1b520d48ae
commit 3e05ffda22
1 changed files with 28 additions and 26 deletions
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54
NanoKernel/NKInit.s
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@ -8,12 +8,15 @@
;_______________________________________________________________________
; This is the entry point for the NanoKernel. Execution always starts here,
; regardless of how the NK was put in control. The immediate purpose of this
; code is to figure out if it was called by the Trampoline bootloader for
; NewWorld Macs or the 'boot' 3 resource on OldWorld Macs. The code path
; diverges dramatically for the 2 cases, so it is important to figure out which
; is which.
; This is the entry point from the Trampoline (our Open Firmware-savvy
; bootloader for NewWorld Macs, which is part of the Mac OS ROM file).
;
; When we receive control:
; If data paging is off, we recieved control from the Trampoline and we are the
; built in NanoKernel. The register assignments are as follows:
; r3 = ConfigInfo
; r4 = ProcessorInfo
; r5 = SystemInfo
@ -21,9 +24,21 @@
; r7 = RTAS_flag ('RTAS' or 0)
; r8 = RTAS_proc
; r9 = HWInfo
; (and also, we can be sure that we are executing from the
; NewWorld ROM image that the Trampoline loaded into RAM)
; r23= SCC (Serial Communications Controller) base address
;
; If data paging is on, we recieved control from the 'boot' 3 resource and we
; are replacing another NanoKernel. The register assignments are as follows:
; LR = return address?
; sprg0 = old KDP/EWA/r1 ptr
; r3 = PA_NanoKernelCode (the physical address of this code)
; r4 = physical base of our global area
; r5 = SCC base address (will be saved to NoIdeaR23)
; r6 = PA_EDP or zero?
; r7 = ROMHeader.ROMRelease (e.g. 0x10B5 is 1.0ß5)
; First we need to avoid executing the data that follows:
b EndOfNanoKernelHeader
@ -45,7 +60,7 @@ EndOfNanoKernelHeader
; Do some sanity checking after receiving control from the Trampoline.
; Figure out how we got control
; cr5_eq is cleared for the builtin init process
@ -59,15 +74,15 @@ EndOfNanoKernelHeader
beql InitBuiltin
; But if data paging is on, do some very strange things...
; But if data paging is on, we are the replacement NanoKernel.
; We need to turn off paging and jump to the replacement init code.
; Does LR contain a return address, or my address, or...?
mflr r9
subi r9, r9, 28
; Prepare to jump to one of the filthy branch instructions
; that Trampoline stuffs into ConfigInfo
addi r12, r3, 64
; Find the physical address of the replacement init code
addi r12, r3, InitReplacement - NKTop; offset
; Unset MSR_POW, MSR_ILE, MSR_EE, MSR_IR and MSR_DR
mfmsr r11
@ -77,22 +92,9 @@ EndOfNanoKernelHeader
; Jump and set MSR with an RFI.
mtspr srr0, r12
mtspr srr1, r11
; We will now be at InitReplacement with paging off
rfi
; This (offset 0x40) is the entry point from 'boot' 3 on OldWorld.
;
; The offset *might* be encoded in the header above!
;
; When we receive control:
; sprg0 = old KDP/EWA/r1 ptr
; r3 = PA_NanoKernelCode
; r4 = physical base of our global area
; r5 = NoIdeaR23
; r6 = PA_EDP or zero?
; r7 = ROMHeader.ROMRelease (e.g. 0x10B5 is 1.0ß5)
;
; For clarity, the NanoKernel-replacement code is included from
; another file. It copies the old kernel structures to a new area
; and adopts them as our own, with some modifications.