TrapdoorSmoke
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Raspbian ARMv7 Image

Tue Nov 24, 2015 5:51 pm

1.Why isn't there a ARMv7 Image for Raspberry Pi 2.
2.Is ARMv6 binarys on Raspberry Pi 2 just as fast as ARMv7.
3.Where is the source code for the packages of raspbian packages like the modified libreoffice package for raspberry Pi or LXDE.

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Paeryn
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 6:18 pm

1. Raspbian includes an armv7 kernel for the RPi2. Everything else is armv6 as then everything works no matter which RPi you plug your SD card into. Plus it saves having to maintain two separate instances of everything when most programs won't notice any appreciable difference.

2. Unless a particular program can take advantage of the extra instructions then you won't really see any difference when compiling for armv7.
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ejolson
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 6:19 pm

TrapdoorSmoke wrote: 2.Is ARMv6 binarys on Raspberry Pi 2 just as fast as ARMv7.
No, however, Raspbian has separate kernels, one for the Pi 2B and the other for the original Pi. The suitable one is automatically selected during boot.
TrapdoorSmoke wrote:1.Why isn't there a ARMv7 Image for Raspberry Pi 2.
Since both CPUs are 32-bit and support hardware floating point, the optimized differences are not very significant for most applications. Since flash cards are easily exchanged between Raspberry Pis it is useful if the same image works in both models. Moreover, people who want an ARMv7 only kernel can choose a different distribution such as Debian.

I posted a graph detailing the slight slow down resulting from ARMv6 compatibility for a parallel code that generates Newton fractals in the forum thread on Intel/MIT Cilk.

TrapdoorSmoke
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 8:14 pm

Is the Broadcom bootcode open source.
So I can make my own armv7 OS

fruitoftheloom
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 8:20 pm

TrapdoorSmoke wrote:Is the Broadcom bootcode open source.
So I can make my own armv7 OS
https://github.com/raspberrypi


http://www.intestinate.com/pilfs


http://wiki.beyondlogic.org/index.php?t ... ot_Process
Last edited by fruitoftheloom on Tue Nov 24, 2015 8:34 pm, edited 1 time in total.
Retired disgracefully.....

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DougieLawson
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 8:30 pm

TrapdoorSmoke wrote:Is the Broadcom bootcode open source.
So I can make my own armv7 OS
NO. The stuff that runs on the GPU is proprietary.

It reads the first primary FAT partition that it finds on the SDCard (/boot in most cases) and loads config.txt (GPU parameters). Those parms tell the GPU how to run the HDMI and which kernel to load (if there isn't a kernel=xxxx.xxx line the GPU loads kernel.img on a Pi1 or kernel7.img on a Pi2). The GPU then reads /boot/cmdline.txt and merges it with some internal parameters. That is passed to the kernel which is booted on the ARM6 or ARM7 processor.

You are free to replace kernel.img or kernel7.img (or a kernel defined in config.txt) with your own code (see the Bare Metal subforum).

You don't need to know what the GPU code is doing because the way it loads the kernel is well documented.
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TrapdoorSmoke
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Re: Raspbian ARMv7 Image

Tue Nov 24, 2015 11:04 pm

So the Broadcom GPU code is closed. :shock:
Thanks

Aydan
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Re: Raspbian ARMv7 Image

Wed Nov 25, 2015 1:03 pm

TrapdoorSmoke wrote:So the Broadcom GPU code is closed. :shock:
Thanks
Yes it is. Just as the GPU firmware on your PC is closed source.

jamesh
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Re: Raspbian ARMv7 Image

Wed Nov 25, 2015 1:12 pm

With regard to Armv7 apps, you can usually just recompile any programs to use ARMv7 and NEON instruction. You can get big speed ups if the code can be parallelised by the compiler (or has dedicated NEON optimizations).

For example, x264 was >30x faster on the Pi2 when encoding H264 when compiled with the right flags. Still ran on the base Raspbian distro.
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Fidelius
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Re: Raspbian ARMv7 Image

Thu Nov 26, 2015 10:30 am

TrapdoorSmoke wrote:So I can make my own armv7 OS
Why not download from the Pi's download page the "Ubuntu Mate 15.10" image and try it out?

It's Ubuntu's ARMv7 Linux, plus Raspbian's Pi² ARMv7 kernel v4.1, plus some Raspbian Pi drivers (like Jamesh' nice hardware mouse cursor, I think. Full list is in this thread). In my experience this ARMv7 Ubuntu runs somewhat faster than Raspbian on a Pi² when you use fat Linux applications like Libreoffice, Firefox, Thunderbird, etc.

Also, since Ubuntu is Debian based itself, you can use this Pi²-Ubuntu very much like Raspbian – just with very up-to-date applications. For example I use a SD-card with Raspbian and XFCE, and a SD-card with this Ubuntu and XFCE, and well, they are very, very similar to use. :-)

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