[RPi 3] Buildroot target options - Cortex A8?

[RiZom-91]

Hi all,

I was wondering why you use the Cortex A8 option in your RPi3 Buildroot configuration ?

RPi3 should be Cortex A53 which is not available without a patch, but default BR config is Cortex A7.

Could someone tells me why you made this change please?

Thanks for your greak work,
RiZom-91

[Substring]

@RiZom-91 Hi,

Easy. As of the release version we used when the Pi3 was released (2015.11 + a few dirty updates after), Cortex A53 was aarch64 only. Later they also implemented A53 as aarch32, but this was not yet released in the last stable branch (we're now on 2016.11). I talked about that with the buildroot team. You could even check their own defconfig for raspberrypi3 : they set it to A7, not A8.

The thing is that we don't want to switch to aarch64. We've had the experience with the Odroid C2, and some emulators don't have JIT or DynaREC ok for aarch64, or even some assembly not compatible.

But I agree with you : I'd love to build for A53 on 32 bits though.

[RiZom-91]

@Substring Ok so A8 is a better choice for RPi3 than A7?

Do you think I can try to build with A53 32bits or it would break a lot of emulators?

Thanks.

[Substring]

@RiZom-91 in fact,i have no idea WHEN the buildroot team will allow aarch32 on A53. I know it works, i tested a minimalistic linux build when they were developping it, it booted up fine. I don't think emulators will break as long as you stay on 32bits. And their changelog shows nothing about that, i didn't browse through their complete commit log neither.

You may eventually ask on their irc channel on freenode, y-morin or kos-tom should know at which stage A53 32 bits is.

And you'd have to merge buildroot in our recalbox-buildroot, of course, which can lead to some conflicts

[RiZom-91]

@Substring Alright, I think there is still something I'm missing. Why did you use A8 instead of A7 which is BR default?

Is A8 more optimized ?

I'm sorry for asking twice, but I think it's important for my understanding!

[Substring]

@RiZom-91 well, can't tell, i'm not the one who did it