random ramblings on 8xx patches (long and tedious :-)

[Dan Malek]

On Jul 22, 2004, at 1:10 PM, Wells, Charles wrote:

> ....... The real problem is that the
> MPC850 USB controller was designed for target-mode applications and not
> host-mode applications.  Host-mode in the MPC850 is, at best, an
> after-thought.

That's true.  Having been a part of the early development of all of the
8xx
parts, there were lots of requirements that changed once the parts "hit
the street."


> 0. The MPC850 USB controller is neither of the popular USB 1.1
> implementation models (UHCI or OHCI).

It's not the only one.  I think there are more embedded controllers that
are not UHCI/OHCI than those that are.  Since we work in the source
code world, it hasn't really been much of a problem.

> ..... I haven't timed it, but I suspect the microcode patch
> has trouble meeting this spec. as well.  It does get a whole lot
> closer than
> a software-only solution, though.

The microcode patch works quite well.

> There's a bunch of other detailed problems that I won't bore everyone
> with.
> Bottom line: Don't expect too much out of the MPC850 USB controller in
> host-mode.

There are Linux versions of software that work fine in many
applications.
USB in general doesn't rate high on my list of engineering successes.
I'm never surprised when I plug something in to any kind of system
and it doesn't work.


	-- Dan


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