Re: MPC8xx binaries running on a MPC82xx board

[Dan Malek <dan@embeddededge.com>]

On Nov 9, 2004, at 11:37 AM, annamaya wrote:

> I was under the assumption that the MPC8xx core was
> different from the MPC82xx core (the 603e?).

Yes, it is different, but the instructions are all the same.

> ...... But I was
> surprised to find that the MPC8xx binaries were
> running fine on a MPC82xx binaries, even if they were
> dynamically linked and were linking to the MPC82xx
> libraries. What's going on here?

Partly luck, and partly that the instructions are the same.
The luck part is you aren't using floating point.  The 8xx
doesn't have hardware floating point, but the 82xx generated
code may have some instructions.  It also depends upon
the tools you are using.  If you were using different glibc
versions, your luck would have run out.

 From a user space application perspective, there are
exactly two differences between 8xx and 82xx.  One is
floating point and the other is cache line size.  The 8xx
software will run fine on the 82xx, but 82xx may not
work properly on 8xx.

> ...... Can I just use the
> 8xx toolkit to work with the 82xx?

An 8xx toolkit will always work on 82xx, but depending
upon the way it was built, you will not get the maximum
performance of the 82xx.  Some tool vendors generate
toolkits (and libraries) specifically for the 8xx, where the
floating point is all emulated in software.  If you were looking
for floating point performance, you would be very disappointed
with this on the 82xx.

> ....... There must be SOME
> differences between these two architectures. Can
> someone here explain this to me?

There are lots of differences in the kernel programming
model, but only the two I mentioned for user space
applications.  In fact, across the entire PowerPC architecture
you will only see floating point, Altivec, SPE, and some
cache line operation/implementation differences at
the user level.  Depending upon your software
requirements and implementation, you are likely
able to run many of the same binaries across all
of the PowerPC cores.

I guess we are rewriting the archives now? :-)


	-- Dan