Re: /dev/vme*

[David Laight <david%l8s.co.uk@localhost>]

On Wed, Feb 13, 2008 at 11:35:30PM -0600, Bolo wrote:
> > > My guess is that they generate the alternate vmebus bus cycle codes
> > > needed to access vmebus devices with 16bit address/data regsiters.
> > 
> > They just allow mapping a different range. That could be allowed for
> > /dev/mem directly as well. That's why I don't see the point in the
> > additional devices.
> 
> My suns are off at the moment, and I don't have current source handy,
> but this may be applicable:
> 
> 1) it would probably break SunOS executable compatability.   The
>       execs can't open the vme address space to access the
>       vme resources there properly.
> 
> 2) IIRC (and it has been a long time) parts of the address space of
> the suns are setup to access the VME bus with different widths.  So,
> yes all it does is map a different range, but that lets the hardware
> do the accesses with the different widths.
> 
> The sun sbus and perhaps mbus memory access may have similar weird mappings,
> but I never really had to deal with that.

Similar stuff could be present for vmebus sparc systems, but the mbus/sbus
systems map everything as 32bit.

        David

-- 
David Laight: david%l8s.co.uk@localhost