How to Hijack the classic Amiga hardware?

[Piru]

@MskoDestny
hwstartup.asm

The code does a bit more than is really needed, and also includes cleanup code, but at least it should give you some idea what needs to be done.

[Piru]

@msh5150

movea.l 4.s,a6 ;Execbase
jsr _LVOForbid(a6) ;Disable multitasking

lea $dff000,a5 ;Custom chip base
move.w #$7FFF,intena(a5) ;Disable interrupts
move.w #$7FFF,dmacon(a5) ;Disable DMA

Forbid is not enough, you must Disable.

If you are running on 68010+ your VBR will be 0 at this point.

There is no guarantee of this. Better not assume anything about the initial VBR value.

[Piru]

@MskoDestny

Tracking down an out of print book is a bit more trouble than making an Amiga port of my little OS is worth to me.

Buy the Amiga Developer CD 2.1, it has full Hardware Reference Manual included (among other priceless documentation). It seems to be available for about 25 eur (or ~30 usd).

Hardware Reference Manual really is essential for programming the HW directly.