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Re: proposal for stateen CSRs

Jonathan Behrens <behrensj@...>
 

Why does all custom state need to be controlled with a single bit? Couldn't we just designate the upper 8 or 16 bits of each xstateenY register to be custom? Any software that wanted to disable all custom state would just clear all those bits, while software that wanted to enable all custom state would just write ones. (WARL would cause any unused bits to stay zero even after they were written with a value of one).

Jonathan


On Wed, Apr 21, 2021 at 12:37 PM John Hauser via lists.riscv.org <jh.riscv=jhauser.us@...> wrote:
Allen Baum wrote:
> If I understand the above: you can write a 1 to the first bit, but you'll
> always read back zero? What does that accomplish?

It provides a convenient means for software to enable lower-privilege
access to all custom state, requiring only the minimal amount of
hardware for the task.

    - John Hauser
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