Re: 答复: [RISC-V] [tech-privileged] RFC: Dedicated Clock Source and Clock Event Source for HS-mode and VS-mode
I see. This is new information for me though. The ‘that is’ in the current spec makes the sentence look like an reiteration of the functionality of the htimedelta itself. I totally didn’t expect this added bit of information about the changing of the trapping rule of the time CSR in there. (Judging from the current implementation in QEMU and KVM, reading time CSR in a virtual machine does trap.) Perhaps add a note to clarify this point?
However, there is still one new bit. Our proposal says that the no-trapping behavior can be turned off, so that the hypervisor can choose to emulate the time CSR for a virtual machine. This can provide the flexibility for implementing simpler systems where the aliases or the htimedelta does not exist.
发件人: Andrew Waterman [mailto:andrew@...]
On Tue, Aug 4, 2020 at 12:46 AM zhaosiqi (A) <zhaosiqi3@...> wrote:
Yeah, my point is that the current definition of htimedelta already says what you want it to say about the time CSR. Reading the time CSR in VS-mode or VU-mode isn't required to trap, and it returns the value you want it to return.