[Libre-soc-dev] svp64 review

lkcl luke.leighton at gmail.com
Mon Jul 25 23:39:56 BST 2022

On Mon, Jul 25, 2022 at 10:27 PM Jacob Lifshay <programmerjake at gmail.com> wrote:

> Because byte-swapping-loads/stores are already a requirement iirc, BE/LE support is generally pretty easy, just xor the BE/LE mode with the byte-swap-or-not bit in the instructions...the only other part needed is byte-swapping the fetched instructions.

yes, the actual hardware is dead-easy.  ldbrx, so the LD/ST *has* to
have byte-swapping.  which means that all you have to do to create
LE/BE is XOR MSB.LE with the one bit in the LD/ST instruction which
selects ldbrx instead of ldx.

in microwatt, the addition of LE/BE support was an 80-line patch.

the hardware's not the problem, at all: it's the software.  you literally
have to compile and then maintain an entire distro.  the only one i know
of that's bothering to do that is Toshaan Bharvani's company,
Ventosh:  https://www.powerel.org/



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