Thanks very much  to all who responded !
I'm still unclear what is accomplished by the BAT register manipulation and
why is it done
TIA
Andy


>This snippet is from ofwboot: Locore.c
>Can somebody kindly explain what's going on here?
>I understand what the instructions do but <why> this is done ?
>Below is the code and  my attempt to decipher it - along with the questions
>Sorry if some of them are clearly in RTFM category
>TIA Andy
>
>
>asm("
>        .text  ; what does the dot here mean?
>        .globl  _start ;what does .globl  mean ?
>_start:
>        li      8,0  	; load zero into register r8 . Why ?
>        li      9,0x100  ; load 0x100 into r9 Why  ?
>        mtctr   	; copy the contents of r9( 0x100 in this case) into
>the count register .Why
>1:
>        dcbf    0,8
> ; data cache block flush - the effective addr in this case = r0 | 0 + r8 -
>what's in r0? why is this done?
>
>        icbi    0,8 	;instruction cache block invalidate - the EA is
>calculated as above - again why?
>        addi    8,8,0x20 ;in this case :r8  = r8+0x20 = 0x20. Correct? Why?
>        bdnz    1b	; -- decrement Count Register and branch to
>location 1b if CTR is not zero. why?? What's at location 1b?
>        sync ; synchronize
>        isync ; instruction synchronize
>
>        lis     1,stack@ha 	 ; r1 = stack<<16 -- what does @ha mean?
>        addi    1,1,stack@l 	; r1 = r1 | 0 +stack - what does @l mean ?
>        addi    1,1,4096  	 ; r1  = r1 | 0 +4096 -- ditto
>			what's the effect of this  ? why is it done?
>
>        mfmsr   8 	;r8  = mfmsr (machine state reg)
>        li      0,0	; r0 = 0 ?
>        mtmsr   0	; msr = r0 ( or zero since we just moved 0 into r0)
>        isync 	' instruction sync
>
>    'why all this manipulation with the instruction BAT upper registrers?
>        mtibatu 0,0
>        mtibatu 1,0
>        mtibatu 2,0
>        mtibatu 3,0
>        mtdbatu 0,0
>        mtdbatu 1,0
>        mtdbatu 2,0
>        mtdbatu 3,0
>
>        li      9,0x12          /* BATL(0, BAT_M) */
>        mtibatl 0,9
>        mtdbatl 0,9
>        li      9,0x1ffe        /* BATU(0) */
>        mtibatu 0,9
>        mtdbatu 0,9
>        isync
>
>        mtmsr   8
>        isync
>
>        b       startup ; well this one i understand:-))
>");