Re: [PATCH v3 3/9] target/riscv: Add the lowRISC Ibex CPU

[Alistair Francis]

On Fri, May 22, 2020 at 12:51 AM LIU Zhiwei <address@hidden> wrote:
>
>
>
> On 2020/5/20 5:31, Alistair Francis wrote:
> > Ibex is a small and efficient, 32-bit, in-order RISC-V core with
> > a 2-stage pipeline that implements the RV32IMC instruction set
> > architecture.
> >
> > For more details on lowRISC see here:
> > https://github.com/lowRISC/ibex
> >
> > Signed-off-by: Alistair Francis <address@hidden>
> > Reviewed-by: Bin Meng <address@hidden>
> > ---
> >   target/riscv/cpu.h |  1 +
> >   target/riscv/cpu.c | 10 ++++++++++
> >   2 files changed, 11 insertions(+)
> >
> > diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> > index d0e7f5b9c5..8733d7467f 100644
> > --- a/target/riscv/cpu.h
> > +++ b/target/riscv/cpu.h
> > @@ -35,6 +35,7 @@
> >   #define TYPE_RISCV_CPU_ANY              RISCV_CPU_TYPE_NAME("any")
> >   #define TYPE_RISCV_CPU_BASE32           RISCV_CPU_TYPE_NAME("rv32")
> >   #define TYPE_RISCV_CPU_BASE64           RISCV_CPU_TYPE_NAME("rv64")
> > +#define TYPE_RISCV_CPU_IBEX             RISCV_CPU_TYPE_NAME("lowrisc-ibex")
> >   #define TYPE_RISCV_CPU_SIFIVE_E31       RISCV_CPU_TYPE_NAME("sifive-e31")
> >   #define TYPE_RISCV_CPU_SIFIVE_E34       RISCV_CPU_TYPE_NAME("sifive-e34")
> >   #define TYPE_RISCV_CPU_SIFIVE_E51       RISCV_CPU_TYPE_NAME("sifive-e51")
> > diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> > index 5eb3c02735..eb2bbc87ae 100644
> > --- a/target/riscv/cpu.c
> > +++ b/target/riscv/cpu.c
> > @@ -156,6 +156,15 @@ static void rv32gcsu_priv1_10_0_cpu_init(Object *obj)
> >       set_feature(env, RISCV_FEATURE_PMP);
> >   }
> >
> > +static void rv32imcu_nommu_cpu_init(Object *obj)
> > +{
> > +    CPURISCVState *env = &RISCV_CPU(obj)->env;
> > +    set_misa(env, RV32 | RVI | RVM | RVC | RVU);
> > +    set_priv_version(env, PRIV_VERSION_1_10_0);
> > +    set_resetvec(env, 0x8090);
> Hi Alistair,
>
> I see all RISC-V cpus  have an reset vector which acts as the first pc
> when machine boots up.
> However, the first pc is more like an attribute of a machine, not a cpu.

In general it seems to be a CPU property. I assume that some CPUs
would allow the reset vector to be selectable though, in which case it
becomes a board property.

>
> Another reason is that the cpu names are a combination of ISA.
> Then the cpus from different vendors may have same ISA, with different
> reset vectors.
>
> Do you think so?

If you are worried about CPUs with different vectors we could always
make it a property in the future and have boards override it. I don't
think we need that yet (only 1 CPU is different) but it is an easy
future change.

Alistair

>
> Zhiwei
> > +    set_feature(env, RISCV_FEATURE_PMP);
> > +}
> > +
> >   static void rv32imacu_nommu_cpu_init(Object *obj)
> >   {
> >       CPURISCVState *env = &RISCV_CPU(obj)->env;
> > @@ -619,6 +628,7 @@ static const TypeInfo riscv_cpu_type_infos[] = {
> >       DEFINE_CPU(TYPE_RISCV_CPU_ANY,              riscv_any_cpu_init),
> >   #if defined(TARGET_RISCV32)
> >       DEFINE_CPU(TYPE_RISCV_CPU_BASE32,           riscv_base32_cpu_init),
> > +    DEFINE_CPU(TYPE_RISCV_CPU_IBEX,             rv32imcu_nommu_cpu_init),
> >       DEFINE_CPU(TYPE_RISCV_CPU_SIFIVE_E31,       rv32imacu_nommu_cpu_init),
> >       DEFINE_CPU(TYPE_RISCV_CPU_SIFIVE_E34,       
> > rv32imafcu_nommu_cpu_init),
> >       DEFINE_CPU(TYPE_RISCV_CPU_SIFIVE_U34,       
> > rv32gcsu_priv1_10_0_cpu_init),
>
>