Re: Smaller embedded version of the Vector extension


Andrew Waterman
 

The uppercase-V V extension is meant to cater to apps processors, where the VLEN >= 128 constraint is not inappropriate and is sometimes beneficial.  But there's nothing fundamental about the ISA design that prohibits VLEN < 128.  A minimal configuration is VLEN=ELEN=32, giving the same total amount of state as MVE.  (And if you set LMUL=4, then you even get the same shape: 8 registers of 128 bits apiece.)

Such a thing wouldn't be called V, but perhaps something like Zvmin.  Other than agreeing on a feature set and assigning it a name, the architecting is already done.

(If you search the spec for Zfinx, you'll see that a Zfinx variant is planned, but only barely sketched out.)


On Wed, Jun 2, 2021 at 3:04 AM Tariq Kurd via lists.riscv.org <tariq.kurd=huawei.com@...> wrote:

Hi everyone,

 

Are there any plans for a cut-down configuration of the vector extension suitable for embedded cores? It seems that the 32x128-bit register file is suitable for application class cores but it very large for embedded cores, especially if the F registers also need to be implemented (which I think is the case, unless a Zfinx version is specified).

 

ARM MVE only has 8x128-bit registers for FP and Vector, so it much more suitable for embedded applications.

https://en.wikichip.org/wiki/arm/helium

 

What’s the approach here? Should embedded applications implement the P-extension instead?

 

Tariq

 

Tariq Kurd

Processor Design I RISC-V Cores, Bristol

E-mail: Tariq.Kurd@...

Company: Huawei technologies R&D (UK) Ltd I Address: 290 Park Avenue, Aztec West, Almondsbury, Bristol, Avon, BS32 4TR, UK      

 

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