Re: Arm Cortex M4 floating point

[Peter Maydell]

On Tue, 18 Aug 2020 at 14:17, Mircea Cociuba <cociuba_mircea@yahoo.com> wrote:
>
> Hello, the netduinoplus2 is not part of the machine list in qemu "QEMU 
> emulator version 4.2.0"
> in which one is it?
> in the 4.1.0 version release notes it says "ARM: FPU emulation support for 
> Cortex-M CPUs, FPU fixes for Cortex-R5F"
>
> Now, is there an option to be passed to qemu to get the FPU working?

I think from 4.1.0 we mostly implemented the FPU for the benefit
of the Cortex-M33 model; we enabled it in the M4 but I don't
know if there are any board models that use it. (You can use
the M4 in the linux-user mode also).

You could either use a newer QEMU version, or see if the QEMU
you have supports a Cortex-M33 board and if that would be
suitable for your needs.

That said, I think looking at the code that the stellaris
board will put a Cortex-M4 in the emulated system if you
use -cpu cortex-m4, though if you do this you are wandering
into unsupported may-or-may-not-work territory. You don't
say what actually goes wrong. (In particular, make sure your
guest code actually enables the FPU via the relevant system
registers before trying to execute fp instructions.)

thanks
-- PMM