bryanpkc
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Booting the Raspberry Pi into big-endian mode?

Mon May 15, 2017 4:28 pm

Has any one successfully booted the Pi in big-endian mode and built/installed a big-endian Raspbian or any Linux on it?

timrowledge
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Re: Booting the Raspberry Pi into big-endian mode?

Tue May 16, 2017 5:20 pm

Why?
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jamesh
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Re: Booting the Raspberry Pi into big-endian mode?

Tue May 16, 2017 6:22 pm

bryanpkc wrote:Has any one successfully booted the Pi in big-endian mode and built/installed a big-endian Raspbian or any Linux on it?
Not that I have heard off. Doesn't sound like a simply task...
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bryanpkc
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Re: Booting the Raspberry Pi into big-endian mode?

Sun May 21, 2017 7:04 pm

timrowledge wrote:Why?
Because I have a couple of Pi's lying around, and have a project to build/debug big-endian code...

MikeDK
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Re: Booting the Raspberry Pi into big-endian mode?

Mon May 22, 2017 2:24 pm

The Endianness is a property of the CPU ... and on the Raspberry it is Little-Endian.

It is not possible to boot into "Big-Endian"-Mode, because the CPU won't understand one single instruction.

Martin Frezman
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Re: Booting the Raspberry Pi into big-endian mode?

Mon May 22, 2017 2:30 pm

MikeDK wrote:The Endianness is a property of the CPU ... and on the Raspberry it is Little-Endian.
ISTR that there do (or did) actually exist CPUs that could be run in either big or small endian mode. So OP's question is not *completely* from outer space.

It'd be interesting to know what OP is actually trying to achieve here...
If this post appears in the wrong forums category, my apologies.

timrowledge
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Re: Booting the Raspberry Pi into big-endian mode?

Wed May 24, 2017 5:52 pm

ARM has been able to do either big or little-endian for some time now. To quote from the ARM ARM DDI 0406A, p. AppxG-7 -
G.3.2 Endian support
ARMv6 supports the same Big Endian (BE) and Little Endian (LE) support model as ARMv7, see Endian support on page A3-7. It is IMPLEMENTATION DEFINED if the legacy big endian model (BE-32) defined for ARMv4 and ARMv5 is also supported. For more information about BE-32 see Endian support on
page AppxH-7.
For configuration and control information, see Endian configuration and control on page AppxG-17.
I really don't understand why anyone would ever use bigendian. It is clearly a violation of the Natural Order Of Things and quite possibly the ill-advised use of it has caused fractures in reality that have left us with the current level of insanity in the political world. Nasty gibbering things from the dungeon dimensions.
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bryanpkc
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Re: Booting the Raspberry Pi into big-endian mode?

Thu Jul 20, 2017 9:40 pm

The network byte order is big-endian, so many embedded network controllers and older (non-smart) cell phones run on big-endian hardware. An ARM CPU can be booted in either big-endian or little-endian mode; it is up to the bootloader to decide which mode the hardware should be in. I was just wondering if the Raspberry Pi bootloader offered a configurable option, and whether any of its other peripherals would prevent the use of big-endian mode. I have a feeling that the GPU would be an obstacle, since it's most likely little-endian only.

timrowledge
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Re: Booting the Raspberry Pi into big-endian mode?

Thu Jul 20, 2017 10:15 pm

bryanpkc wrote:The network byte order is big-endian.
Irrelevant; ARM provides instructions for all sorts of ways to handle big-endian-evil.

For example
REV Rd, Rm ARMARM DDI0406Q p. A8-270
REVSH Rd, Rm ibid. pp A8-274-5
REV16 Rd, Rm ibid. pp. A8-272-3

Unless you have some near-magical way to get data in and out so fast that spending an instruction endian-swapping before and after any other manipulation is significant, I don't see much likelihood that you need anything else.
Making Smalltalk on ARM since 1986; making your Scratch better since 2012

beta-tester
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Re: Booting the Raspberry Pi into big-endian mode?

Fri Jul 21, 2017 7:22 pm

bryanpkc wrote:Has any one successfully booted the Pi in big-endian mode and built/installed a big-endian Raspbian or any Linux on it?
what sense does it make, when you use a rich opperating system ontop.
i would understand, when you are using your RPi in "raw-/bare- mode" without an opperating system (visit that section Bare metal).
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