Re: Detecting the Zbb extension on riscv64

[Resending with the right From: so it reaches the list...]

On 2 Jun 2024, at 19:33, Robert Clausecker <fuz@freebsd.org> wrote:
> 
> Hi Michael,
> 
> Am Sun, Jun 02, 2024 at 06:37:44PM +0200 schrieb tuexen@freebsd.org:
>>> [U74 Core Complex Manual]: https://starfivetech.com/uploads/u74_core_complex_manual_21G1.pdf
>> Thanks for the pointer. Zbr is not mentioned there...
> 
> It's not mentioned (though the next revision mentions Zba and Zbb), but
> the instructions of Zba and Zbb are listed as being available.

The U74 has evolved over many years with multiple versions. The
Unmatched has a version from late 2018 (its mimpid is 0x20181004 as
printed at boot) which predates Zb* ratification. You need to look at
the manual for the board in question[1], not StarFive’s manual
corresponding to their newer board and thus core revision.

Jess

[1] https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf