Re: Smstateen for Zcmt


Tariq Kurd
 

ok, thanks John, I've done the rewording.

Tariq

On Mon, 23 May 2022 at 02:46, John Hauser <jh.riscv@...> wrote:
Tariq Kurd wrote:
> Therefore, I'd like to allocate one Smstateen bit to JVT - the CSR only.

> Can I allocate bit 2 as follows?

Yes, let's assume bit 2 is allocated for this purpose, in mstateen0,
hstateen0, and sstateen0.

> *Bit 2 applies only for the case that Zcmt is implemented, which includes
> the JVT CSR and the cm.jt, cm.jalt encodings.*
> *For convenience if bit 2 of a controlling stateen0 CSR is zero, then all
> cm.jt, cm.jalt instructions cause an illegal instruction trap *
> *(or virtual instruction trap, if relevant). *
>
> How does that sound?

We'll probably change the wording later, but for now, replace the
word _encodings_ by _instructions_, and drop "For convenience".
Instructions CM.JT and CM.JALT must trap because they implicitly depend
on the value of jvt.

> ..and I'm not proposing a stateen for Zcmb, Zcmp, Zcmpe.

Right.  The intention is that stateen bits should be for controlling
access to new state.  No state, no stateen bit.

    - John Hauser


--

Tariq Kurd | Chief CPU Architect | Codasip UK Design Centre | www.codasip.com

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