Subject: Re: 4xx - a question and a patch

From: Dan Malek <[email-masked]>
Date: Wed, 05 Sep 2001 00:18:30 -0400

David Gibson wrote:

> The 405gp manual implies that an mtspr to the PIT writes both the
> decrementing value and the reload register.  Is this a hardware /
> documentation bug?

Well, the point is that it writes the reload register.  When it
gets to zero, it reloads with this register, which is wrong.

> .....  Could the PIT be used this way if auto-reload was
> disabled?

No, because the PIT doesn't count down past zero.  If they would
have allowed this, we could have disabled the auto-reload and
treated it just like the decrementer.

The best I could come up with is just allow the PIT run with a
proper and fixed reload value.  It isn't a decrementer and we
can't treat it like one.

> Sure, but it's still useful to be able to run binaries copied from
> "normal" PPC machines.

Just remember that you can't be mixing float emulation and in-line
floating point software.

	-- Dan

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