[RISC-V] [tech-chairs] Architecture extension proposal for ConfigPtr CSR to "Unified RISC-V Discovery Method" config structure

Robert Chyla <Robert.Chyla@...>

I think we can extend meaning of that CSR register (for future) by allowing write of some 'keyed/secret' value into it.
Keeping it 'clean address' is IMO better for now.


On 6/28/2021 1:54 PM, Philipp Tomsich wrote:

On Mon 28. Jun 2021 at 22:40, Greg Favor <gfavor@...> wrote:
On Mon, Jun 28, 2021 at 1:29 PM Tim Newsome <tim@...> wrote:
One addition:
If the CSR contains 0, software should assume there is no configuration structure.

I'd also like to require the pointer be 4-byte aligned, meaning software should ignore the low 2 bits. This will give us 2 extra bits should we need them in the future.

That's OK.  The extension would then define the low two bits as "00" and as "Reserved for future standard use".

In consideration of low-end systems that may point into some memory-mapped serial storage, I would rather avoid this.

It’s also going to cause eventual discussions, once the first devices with errata slip through and cause issues with software ghat assumes this constraint to always hold.


Robert Chyla, Lead Engineer, Debug and Trace Probe Software
IAR Systems
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E-mail: Robert.Chyla@... Website: www.iar.com