Re: Detecting the Zbb extension on riscv64

> On 2. Jun 2024, at 15:42, Robert Clausecker <fuz@freebsd.org> wrote:
> 
> Hi Michael,
> 
> Am Sun, Jun 02, 2024 at 03:05:09PM +0200 schrieb tuexen@freebsd.org:
>>> Zbb is supported by the SiFive unmatched board for example.
>> just double checking:
>> According to
>> https://sifive.cdn.prismic.io/sifive/d0556df9-55c6-47a8-b0f2-4b1521546543_hifive-unmatched-datasheet.pdf
>> the processor supports RV64GC (RV64IMAFDC). I don't see a B there.
>> So does it actually support Zbb? What about Zbr?
> 
> The board is based on the SiFive FU740-C000 SoC, which uses
> a quad-core U74 CPU.  Reading the [U74 Core Complex Manual],
> we find that it supports the Zba and Zbb instruction set
> extensions.
> 
> [U74 Core Complex Manual]: https://starfivetech.com/uploads/u74_core_complex_manual_21G1.pdf
Thanks for the pointer. Zbr is not mentioned there...
> 
> Though on the other hand, if I actually try to execute a program
> using the CTZ instruction, I get a SIGILL... what's going on here?
I don't know.

Best regards
Michael
> 
> Yours,
> Robert Clausecker
> 
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