Re: Platform specification questions

Ved Shanbhogue

On Sun, Dec 12, 2021 at 7:55 PM Anup Patel <anup@...> wrote:
Since, both OS-A platforms with M-mode and M platforms need ACLINT
MTIMER so I suggest that OS-A platforms should say "If M-mode is
implemented then ACLINT MTIMER should be supported ...".
I was thinking along the lines of how Greg was thinking here.

On Sun, Dec 12, 2021 at 08:43:30PM -0800, Greg Favor wrote:
This separates out from the current OS-A platform specs the ACLINT MTIMER
device as a standardized Machine-level implementation of the MTIME and
MTIMECMP registers defined in the Priv spec.

Now, for systems that implement Priv 1.12 and the Sstc extension, and
actually use the Sstc extension, then this can be the end of the story.

But for today's systems and for future systems that don't implement Sstc
(unless all OS-A 2022 platform specs were to mandate Sstc support and
eliminate any possibility of existing systems complying with at least the
Embedded (i.e. old "Base") OS-A platform spec), they also need the SBI API
that provides Supervisor timer functionality to S/HS mode (with M-mode
using MTIME and MTIMECMP to provide that functionality). While this is
also an SEE interface, talking about this does start to sneak up on talking
about MTIME. But then again one could still abstract MTIME as the system
timebase, and MTIMECMP as a timebase compare value.


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