On Mon, Jun 17, 2019 at 07:47:36PM +0200, Arno Steffens wrote: > Thanks for explaining this. > I take some time to read about thumb/thumb2. The feedback is mixed. It seems > to generate more compact code, but some say it speeds up, others it slows > down because of reduced function set - and it can cause strange effects. > And mixing this causes time to switch processor mode. So, as I am not an > expert in this and can't decide what ist best on per function base and speed > is of highest priority, I think I better should use not thumb(2). > > So, do I get it right that with this cortexa9t2hf I just have the option to > compile it for thumb2? But without using a dedicated compiler option it > generates same "standard" arm code and the difference is just to adapt all > the Makefiles for this suffix. > > According to Martin I can get the previous setting by just set > ARM_INSTRUCTION_SET to "arm" instead of "armv7a". Mh - I just afraid that I > lose other kinds of optimisation. (I am just a user not an expert in arm > architecture).
I didn't say anything about changing the DEFAULTTUNE. Just ARM_INSTRUCTION_SET to "arm" which will give you "cortexa9hf" again (not "armv7a"). > On the other hand for those like me it is better go the standard way. Once I > am sure compiler results will not become worse (see above) I go for the pain > and renaming my toolchain/makefiles/stuff. The results should be almost the same, maybe slightly better, depends on the actual code as Khem mentioned. But if this causes you a lot of pain "renaming my toolchain/makefiles/stuff" then you should probably spend the time on your tooling instead of replacing one hardcoded value with another. Cheers, > > Thanks for you taking the time. > Arno > > > Hello Arno, > > > > Let me try to explain my point of view. Since here (my best guess) we > > have some asynchronous bitbake code which went South upon introducing > > T2 HW extension. > > > > Point [1]: as far as I understand arm, cortexa9t2hf is is just a > > superset of previous cortexa9hf (HW wise). NEON HW extension (NEON > > media coprocessor) exists in both of them. In other words: > > cortexa9t2hf = cortexa9hf HW + T2 HW extension. > > > > Point [2]: > > > bitbake gives me in 2.5: > > > TUNE_FEATURES = "arm armv7a vfp thumb neon callconvention-hard > > > cortexa9" > > > TARGET_FPU = "hard" > > > > > > and in 2.7: > > > TUNE_FEATURES = "arm vfp cortexa9 neon thumb callconvention-hard" > > > TARGET_FPU = "hard" > > > > These two lines are the same: you are able to use 32b arm mode, 16bit > > thumb mode, using armv7 HW with neon HW extension, and using HW FP > > extension as well. The Cortex in both cases is A9. > > > > I expect that somebody somewhere in bitbake version 1.42 - 100% sure > > (since 2.5/Sumo uses bitbake 1.38) dropped "armv7a" as TUNE FEATURE, > > and I have no idea if this is done intentionally or not. > > > > Because of that I copied Alex and Ross to CC: into email, so they > > should unveil this mystery (I would prefer "armv7" to stay in bitbake > > 1.42, since A8 and A9 belongs to armv7, A15 belongs to armv8 (IIRC). > > > > Bottom line: nothing to be done by you, Arno, seems that bitbake 1.42 > > should return "armv7" as TUNE FEATURE. > > > > Best Regards, > > Zoran > > _______ > > > > > > On Mon, Jun 17, 2019 at 3:00 PM Arno Steffens <s...@gmx.li> wrote: > > > > > > Hello Zoran, > > > thanks. As far as I understand is thumb2 another mode of coding, that > > > might create more compact code. > > > But I want to keep all compatible to my previous tool-chain and settings. > > > The only file where I can found this "cortexa9t2hf" is > > > ./meta/conf/machine/include/tune-cortexa9.inc > > > but I can't see how I can control Yocto to generate "cortexa9hf-neon" as > > > before. > > > Or have I been wrong the time before? > > > > > > bitbake gives me in 2.5: > > > > > > TUNE_FEATURES = "arm armv7a vfp thumb neon callconvention-hard > > > cortexa9" > > > TARGET_FPU = "hard" > > > > > > and in 2.7: > > > TUNE_FEATURES = "arm vfp cortexa9 neon thumb callconvention-hard" > > > TARGET_FPU = "hard" > > > > > > so armv7a seem to be missing. In terms of thumb both is same. But is that > > > the reason? Where to set it? > > > Arno > > > > > > > > > > > Hello Arno, > > > > > > > > Your question, per say, has little to do with YOCTO forum. But I'll > > > > try (as my best) to answer your question. > > > > > > > > Cortexa9hf should be armv7 A9 Hard Floating (it contains HW FP unit). > > > > > > > > Cortexa9t2hf is by analogy armv7 A9 T2 Hard Floating. Now, the > > > > question is what is T2? T2 is addition to the previous architecture > > > > Cortexa9hf, and addition is Thumb-2 mode. > > > > > > > > Hope this helps, > > > > > > > > Zoran > > > > _______ > > > > > > > > On Mon, Jun 17, 2019 at 2:03 PM Arno Steffens <s...@gmx.li> wrote: > > > > > > > > > > I switched from Yocto 2.5 to 2.7 and recognised a new architetcure > > > > > name. > > > > > Instead of cortexa9hf it is now build for cortexa9t2hf? Did I do > > > > > something wrong or what exactly does this t2 mean? > > > > > Target system is a Zynq7020 system. > > > > > -- > > > > > _______________________________________________ > > > > > yocto mailing list > > > > > yocto@yoctoproject.org > > > > > https://lists.yoctoproject.org/listinfo/yocto > > > > > > > -- > _______________________________________________ > yocto mailing list > yocto@yoctoproject.org > https://lists.yoctoproject.org/listinfo/yocto -- Martin 'JaMa' Jansa jabber: martin.ja...@gmail.com
signature.asc
Description: Digital signature
-- _______________________________________________ yocto mailing list yocto@yoctoproject.org https://lists.yoctoproject.org/listinfo/yocto
