[parisc-linux] Questions understanding exec_kernel
Wed, 22 Sep 1999 15:32:24 +0200
> > [Question: Page 5-149 from the PA-RISC 1.1 Architecture and Instruction
> > Set Reference Manual states: "Level 0: If the target control register
> > is CR 8, 9, 12, 13, 17, or 20, this instructin executes as a null
> > instruction." I am assuming we are running at level 0 since the rfi
> > command required running at level 0, so what is the difference between a
> > null instruction and a nop?]
There is none. Null instructions (here) refer to instructions ignored since
they don't apply to the specific hardware. Nops are usually regular forms of
arithmetic / logical instructions that happen to do nothing.
> That's an easy one:
> Nullfied instructions are simple ignored - output discarded.
Except we're not talking about nullified instructions :)