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Re: [Qemu-devel] [PATCH] Target-arm: Add the Cortex-M4 CPU

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH] Target-arm: Add the Cortex-M4 CPU
Date: Fri, 29 May 2015 14:21:45 +0100

On 29 May 2015 at 13:55, aurelio remonda <address@hidden> wrote
> Perhaps we could commit this now and add the VFP in the future?

That's how we've generally worked, yes -- if you just ask
for a "Cortex-A9" or whatever you get the maximum set of
features that CPU can support (so always Neon & VFP even if
some A9 hardware is configured without VFP), and if we add
support for a feature that the hardware has after the
CPU model was first added then we add the feature to that
CPU. (So we didn't have TrustZone support when the A9
was initially put into QEMU, but when we put in the TZ
support we turned on the ARM_FEATURE_EL3 bit for the A9 by

If we need to also support CPUs of that model that don't have
a particular optional feature we can do that via a CPU property
(as we do with 'has_el3' for disabling TZ support). Then a board
that wants an M4 without FPU can set the property to false, or
a user who wants to control it from the command line can do so
via -cpu cortex-m4,has-fpu=false or similar.

-- PMM

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