[libre-riscv-dev] SV auto-width

[Jacob Lifshay]

We will still need a way to convert between vectors with different element
sizes that's faster than ld/st.

Jacob

On Tue, Jan 8, 2019, 04:34 Luke Kenneth Casson Leighton <lkcl at lkcl.net
wrote:

> talking on comp.arch has been extremely useful.  the guy who developed
> the mill architecture pointed out that dynamic auto-width is
> problematic in several ways.
>
> given that it will:
>
> (a) require adjustment to the compilers
> (b) need to be at the maximum bitwidth of src and dest
> (c) not be well understood (resulting in bugs)
> (d) need a special (micro-code-like) pipeline stage to do the conversion
> (e) mean that the architectural design has to be adjusted
>
> i'm inclined to *not* support dynamic auto-width in the Libre RISCV
> SoC, and to even remove it from the SV specification entirely.
>
> thoughts?
>
> l.
>
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