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Re: [Qemu-devel] [ARM]: Adding support for Cortex-M4

From: Peter Maydell
Subject: Re: [Qemu-devel] [ARM]: Adding support for Cortex-M4
Date: Tue, 5 May 2015 14:04:01 +0100

On 5 May 2015 at 13:52, aurelio remonda <address@hidden> wrote:
> Hi, i would like to to add support for cortex-m4 on qemu. Most features of
> the Cortex-M3 and M4 are the same with the significant difference that
> Cortex-M4 has DSP extensions and optional FPU. Even so, i really need some
> pointers for this (im a newbie on qemu devel). I found out that qemu can
> manage dsp instructions such as ADD16, ASX, SAX, etc. and all their
> combinations with suffixes (u, s, sh, etc.), so half (if not all) of the
> work is done.

To quote something from the mail I wrote last time somebody
asked about Cortex-M4:

The instructions themselves are generally supported for
the A profile cores, so getting that part right would mostly
involve enabling those feature bits for the new M4 CPU class.
The difficult bits are going to involve:
 * correct trapping when fp is disabled
 * getting the exception handling right, including lazy
   exception frame population
 * bits where M profile FP differs from A profile (eg fp
   status and ID registers being memory mapped)

> How should I go about this? What's the standard procedure for adding a new
> CPU, even if it's so similar to the existing ones? That is, which are the
> relevant functions/files that I should modify, and so on.

For a new ARM CPU, the files you want are all in target-arm/.

-- PMM

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