[libre-riscv-dev] sv.setvl encoding

Luke Kenneth Casson Leighton lkcl at lkcl.net
Fri Jun 28 04:54:06 BST 2019

On Thu, Jun 27, 2019 at 11:38 PM Jacob Lifshay <programmerjake at gmail.com> wrote:
> I added the encoding I had originally planned under the "original encoding"
> header.
> https://libre-riscv.org/simple_v_extension/specification/sv.setvl/

 ok so SV is never going beyond RV64 without a major redesign as VL
and MVL are compacted into 6 bits (RV128 has XLEN=1<<7).

 so, the field named MAXVL, practically speaking, need only be 6 bits, not 11.

 the MAXVL field fits across the rs2 field rather than the top
immediate bits (normally a funct5/6/7).  which would complicate
brownfield encoding that wanted an rs2.


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