[ydl-gen] String instructions emulation on PPC970MP

[Derick Centeno]

Hi Patrice:

I did a little digging and came across the following explanation from IBM
which explains that the CPU you are coding for (amcc440) requires a specific
Linux capable of the following:

In versions 2.6.26 and earlier of the Linux kernel, the code did not
properly clear reserved bits 11 - 15 in word two of a Translation Lookaside
Buffer (TLB) entry. These bits need to be set to zero as documented in the
respective user’s manuals to avoid a degradation in performance.
A change was included in Linux kernel version 2.6.27 which will clear
reserved bits 11 - 15 bits in the finish_tlb_load function. With these bits
automatically cleared, inadvertent performance degradation will be avoided.
Users of the PPC440x6 and all 464 processor cores should use Linux kernel
version 2.6.27 or later.

You can read the document for yourself here:

https://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/6F95C69A2ED9AE73002575AF005B6E4E

YDL 6.2 does use kernel 2.6.27 (see here:
http://www.fixstars.com/en/products/ydl/installed.html) however make sure
that the settings recommended by IBM are in effect for the amcc440.
However, that would mean that you are directly coding for that cpu not the
native 970MP which comprises the PowerStation which would explain the
problems you are reporting.

IBM does have a document explaining coding for the 970MP (which are the
native cpus within the PowerStation) and the Linux parameters they
recommend.  That document is here:

https://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/A0C294269DB8D1EC87256FF9004FC54C

These are just preliminary references, of course, but I thought the
information could be a useful start for you.  As for acquiring more details,
you may have to confer with someone at Fixstars.

All the best...

On Tue, Dec 8, 2009 at 8:08 AM, Patrice B <pbfwdlist at gmail.com> wrote:

> Hello,
>
>  I'm using a Power Station as a build machine to generate code for
> amcc440 cpu using gcc 4.4 with option -mcpu=440fp. Since this release
> of gcc, I notice that code is generated with string instructions which
> are not supported by Power Station cpu, and then, it makes build
> failed if a newly built binary needs to be run for a next build step.
> Is there a way to emulate those instructions on a Power Station (which
> currently runs YDL 6.0)
>
>  Best regards
>
>        Patrice
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