Re: [Qemu-devel] [RFC 1/2] target/arm: add "cortex-m0" CPU model

[Peter Maydell <peter.maydell@linaro.org>]

On 2 June 2018 at 15:14, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> Define a "cortex-m0" ARMv6-M CPU model.
>
> Most of the register reset values set by other CPU models are not
> relevant for the cut-down ARMv6-M architecture.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  target/arm/cpu.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 5d60893a07..aac224d809 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -1215,6 +1215,16 @@ static void arm11mpcore_initfn(Object *obj)
>      cpu->reset_auxcr = 1;
>  }
>
> +static void cortex_m0_initfn(Object *obj)
> +{
> +    ARMCPU *cpu = ARM_CPU(obj);
> +    set_feature(&cpu->env, ARM_FEATURE_V6);
> +    set_feature(&cpu->env, ARM_FEATURE_M);
> +
> +    /* TODO ARMv6-M doesn't support coprocessors, so how is this value accessed? */
> +    cpu->midr = 0x410cc200;

The MIDR is a memory-mapped register on M-profile (at 0xed00ed00);
we implement this in hw/intc/armv7m_nvic.c.

> +}
> +
>  static void cortex_m3_initfn(Object *obj)
>  {
>      ARMCPU *cpu = ARM_CPU(obj);
> @@ -1796,6 +1806,8 @@ static const ARMCPUInfo arm_cpus[] = {
>      { .name = "arm1136",     .initfn = arm1136_initfn },
>      { .name = "arm1176",     .initfn = arm1176_initfn },
>      { .name = "arm11mpcore", .initfn = arm11mpcore_initfn },
> +    { .name = "cortex-m0",   .initfn = cortex_m0_initfn,
> +                             .class_init = arm_v7m_class_init /* TODO rename? */ },

We use v7m for a lot of stuff that's really M-profile in
general (eg the v8m cortex-m33), so I wouldn't worry too
much about renaming the function.

thanks
-- PMM