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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, 26 May 2015 18:34:28 +0100

On 26 May 2015 at 18:13, aurelio remonda <address@hidden> wrote:
> There are 85 instructions labeled as DSP (all of them thumb2), im just
> testing on disas_thumb2_insn if the feature is enabled before the
> instruction is generated.i.e.
> if (!arm_dc_feature(s, ARM_FEATURE_DSP)) goto illegal_op;
> Im using DDI0439B_cortex_m4_r0p0_trm - Cortex-M4 Technical Reference Manual
> (there's s table of dsp instructions on page 33) and this
> http://www.lpcware.com/system/files/1100969_Cortex-Inst.jpg as reference.

Ah, right. I suggest we call this
 ARM_FEATURE_THUMB_DSP  /* DSP insns supported in the Thumb encodings */
and in arm_cpu_realizefn() just after the bit where we set ARM_FEATURE_CBAR
you want:
    if (arm_feature(ARM_FEATURE_THUMB2) && !arm_feature(ARM_FEATURE_M)) {
        set_feature(env, ARM_FEATURE_THUMB_DSP);

because all A and R profile cores with Thumb2 have these instructions.
You'll also want to set the THUMB_DSP feature bit for your new M4
core in its cortex_m4_initfn(), and that should be enough.

(I think "THUMB_DSP" is better than "DSP" because in the ARM encoding
we won't look at this feature bit, because the presence of the insns
is determined by the architecture version -- some come in in v5 and the
rest in v6.)

For floating point, is it sufficient to turn on ARM_FEATURE_VFP4 for
the M4, or does that enable too much?

-- PMM

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