[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal
luke.leighton at gmail.com
Sat Aug 10 17:03:01 BST 2019
On Friday, August 9, 2019 at 7:12:00 PM UTC+1, Allen Baum wrote:
Well, one way to get at the underlying HW characteristics is an ECALL to a
> higher priv mode; That will take a little longer, but I don't see why it
> would be used more than once during the run of an applications, so that
> should be OK.
i think samuel pointed out that this is (sorely) needed: there was
something where, at the moment, you have to get at some information right
at boot time then "hope like hell it never gets changed". providing a
mechanism for user-space to call up to higher priv levels would fix that.
> But a similar issue has come up in several forums, and I've proposed a
> standard discovery mechanism that will enable all kinds discovery using a
> CSR interface.
> Writing the CSR initializes a pointer into a discovery data structure, and
> reading it will return the contents of the structure at that offset (with
> optional autoincrement)
> The data structure is a linked list of capabilities (ID, offset of next
> capability) where the actual capability is implementation dependent (on the
> So, a config string ID, debug capability ID, ISA capability ID can be
> independently defined to be YAML, binary or ascii formats, as desired.
More information about the libre-riscv-dev