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Re: [Qemu-riscv] [Qemu-devel] [PATCH v2] target/riscv: Hardwire mcounter

From: Jonathan Behrens
Subject: Re: [Qemu-riscv] [Qemu-devel] [PATCH v2] target/riscv: Hardwire mcounter.TM and upper bits of [m|s]counteren
Date: Wed, 3 Jul 2019 14:02:56 -0400

Bin, that proposal proved to be somewhat more controversial than I was expecting, since it was different than how currently available hardware worked. This option seemed much more likely to be accepted in the short term.


On Mon, Jul 1, 2019 at 9:26 PM Bin Meng <address@hidden> wrote:
On Tue, Jul 2, 2019 at 8:20 AM Alistair Francis <address@hidden> wrote:
> On Mon, Jul 1, 2019 at 8:56 AM <address@hidden> wrote:
> >
> > From: Jonathan Behrens <address@hidden>
> >
> > QEMU currently always triggers an illegal instruction exception when
> > code attempts to read the time CSR. This is valid behavor, but only if
> > the TM bit in mcounteren is hardwired to zero. This change also
> > corrects mcounteren and scounteren CSRs to be 32-bits on both 32-bit
> > and 64-bit targets.
> >
> > Signed-off-by: Jonathan Behrens <address@hidden>
> Reviewed-by: Alistair Francis <address@hidden>

I am a little bit lost here. I think we agreed to allow directly read
to time CSR when mcounteren.TM is set, no?


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