On Jun 12, 23:27, Chris G Demetriou wrote:
> Subject: Re: pthreads
> > I believe the reason TAS won't work is an OS thing, not a hardware thing,
> > but I may well be wrong.

As far as I recall it from the introduction to the RKM Manuals the reason
why one can not use TAS instructions is with the hardware:
The AMIGA shares the memory bus between many components (CPU, blitter,..)
There is a fixed scheme, which cycles can be used by whom.
Especially the CPU is denied access to the bus whenever display or
blitter access has to be done.
It would be impossible to keep the CPU from accessing the bus with
an undividable RWM cycle of the TAS instruction.



> 
> I'd believe that, but...
> 
> TAS is present in every m68k processor that i've got manuals here for
> (admittedly, only the '020 and '030, but i don't recall it being one
> of the instructions that has to be emulated in either the '040 or
> '060).
> 
> TAS is not a privileged instruction.
> 
> 
> Given that, the only places where the OS _could_ be involved are:
> 	(1) in the possible handling of faults related to read/write
> 		operation, and
> 	(2) in dealing with caching issues.
> 
> It's not clear to me how the OS could get either of those 'wrong' in
> such a way that TAS wouldn't be usable...
> 
> 
> (Note that everything that i've mentioned above applies to CAS and
> CAS2, as well...)
> 
> 
> 
> chris
>-- End of excerpt from Chris G Demetriou


Just my $0.04 (tax incl.)

Bye...
	Stephan