On Sat, Feb 15, 2025 at 01:20:23PM +0100, Martina Hřebcová wrote: > Hi all, > > I have one question about kernel / debian operation. > > I have computer A1222+ with CPU P1022 ( two e500v2 cores ). It is NG Amiga > with AmigaOS4, but linux runs here nice too. > > P1022 CPU is 32-bit powerpc processor, it has no powerpc FPU but have > embedded SPE FPU instead. Also it has SPE SIMD unit. It has no FP or vector > registers, instead it has GPRs extended for 64bit for FPU and SIMD > operations. So it has different ABI than standard powerpc for floating-point > parameter calls. > > There was in past powerpcspe port of Debian. It was dropped somewhere in > 2016, due to excluding of SPE extension from gcc. > > Debian 8+ powerpcspe snapshot from these times runs very well, with full 3D > desktop support. There is customized kernel for A1222+, which was maintained > by xeno74. Last version I found is 5.4. All this is normal and expected. > > There are no other native powerpcspe distro ( or at least I am not hear > about it). > > But now I tried standart powerpc Ubuntu 16.04 and also last version of > powerpc 32-bit Void linux. > > If I used custom kernel from xeno74 and standart powerpc distro, it works on > my powerpcspe machine with different ABI. > > ( So now I have in plan to install more modern Debian from snapshots, or > Fienix distro, which is based on modern Debian ) > > Please, how does it works? How is possible that powerpc code with fpu not > crashes? > > I can imagine, that in custom kernel there are soft-float calls. But there > shoud be some powerpc FPU emulator or what... > > Please, do you have any idea?
Any software that doesn't use FPU at all should work I believe. Any that uses FPU would not, unless the kernel happens to be configured to emulate an FPU. I can't remember if powerpc ever had an option to do that. I know some architectures in the past did at least. Looking at the kernel config, it appears CONFIG_MATH_EMULATION exists and may in fact do just that. In fact I found some discussions from 8 years ago that said tha A1222 can in fact run powerpc code with the MATH_EMULATION kernel option enabled. It's not recommended, since the FPU performance is terrible. I will continue to despise the A1222 even existing for the fact they put that garbage CPU on it that is not a proper powerpc and broke all existing compatibility of AmigaOS 4 FPU using code. -- Len Sorensen
