On Tue, May 20, 2003 at 09:07:26PM +0200, Kevin D. Kissell wrote:
> I don't remember the discussion in question, but it's a question
> which comes up from time to time, due to the existence of
> MIPS-like CPUs which lack the (patented) lwl/lwr mechanism
> for dealing with unaligned data. The Lexra cores, for example.
> There's really no such thing as "disabling" lwl/lwr. They are part
> of the base MIPS instruction set. If one wants to live without them,
> one can either rig a compiler to emit multi-instruction sequences instead
> of lwr/lwl to do the appropriate shifts and masks (which is slower on all
> targets), or you can rig the OS to emulate them, and hope that the processors
> lacking support will take clean reserved instruction traps, where the
> can be emulated (which is "free" for code running on CPUs with lwl/lwr,
> but *really* slow for the guys doing emulation).
Technically you're right ... In reality lwl/lwr are covered by US patent
4,814,976 which would also cover a software implementation. So unless MIPS
grants a license for the purpose of emulation in the Linux kernel ...