Difference between sun4, sun4c and sun4m subarchitectures

[Doc Shipley]

der Mouse wrote:

>>>Does anyone know what are the real technical differences between
>>>sun4, sun4c and sun4m subarchitectures of SPARC from the viewpoint
>>>of an OS kernel writer?  [...] Net/OpenBSD has a unified SPARC
>>>kernel, [...]
> 
> I just had a quick look at the NetBSD code.  The biggest differences
> seem to be in the pmap, which deals with the MMU; there are other
> checks for SUN4 vs SUN4M vs SUN4C scattered around, but they are mostly
> various drivers that know things like "this device appears attached to
> obio only on 4c machines".  It's possible to build a kernel supporting
> any desired subset of the three types; if you build a kernel supporting
> more than one type, you will pay a marginal speed penalty since some
> things will make run-time checks for the architecture, checks which are
> effectively done at compile time in a single-architecture kernel.

<snip>

> You might want to check it before suggesting it.  I just had a look and
> found nothing of any real use to an OS writer.  It talks only in
> generalities far too vague to write code to.

   First, I lost the original post by MS, so the attribution is fuzzy. 
Sorry.  Sue me.  ;)

   Second, I'm certain that the core technology of the 32-bit SPARC 
processors is open and published.  There are even a couple of FPGA 
implementations of the early ones out there.

   I don't know where the specific docs are, but I can ask if it sounds 
relevant.


	Doc