Order of the Butterfly
Posts: 301 from 2003/2/24
From: Genesi
Quote:
ARM does support Big Endian, so I am quite perplexed by your comments there. Only the XScale model does not. That eliminates 1 series out of dozens. And nobody is proposing that we get silicon, at least, not at this time. But having the option, should it present itself, would be a worthly long term goal.
ARM doesn't support Big Endian in anything but a bullet-point feature sense.
The same is true of PowerPC processors which supposedly support Little Endian operation.
The basic promise made in supporting these features is that it reorders bus transactions so they fit the right data format - memory is laid out in Big Endian, but when you load it into a register, it is flipped automatically and in the register on your Little Endian processor, you have Little Endian data.
On PowerPC, you can fudge this manually without changing modes at all if you know the data format ahead of time (stwbrx, lwbrx). I'm not sure what the equivalent is on ARM.. maybe it doesn't have it, maybe it does.
Instruction opcodes are still Little Endian in ARM whatever mode it's in. Internal registers and devices are all Little Endian. All that changes is how it routes data from memory into the cache and then the register. It is a limited subset.
The SOLE reason for these features is because both ARM and PowerPC targets can and do run as device targets (e.g. on a PCI bus with another host processor doing the control) and they need to be able to interoperate with those buses. It does not magically turn your system into a Other Endian chip, it just aids interoperability - the same way that running Samba 4 on a Linux box does not mean you have a Windows 2008 Domain Controller, it just means you have a subset of the functionality which look for all intents and purposes like you do (you are basically not running Windows, so don't expect every feature of Windows!)
However absolutely NONE of this is relevant to MorphOS. MorphOS is for all practicality endian-independent - the only reason it gets thorny is trying to mimic PowerPC and/or m68k operation. So, the solution is.. drop those things in the trash where they belong. MorphOS has plenty of developer support and a huge amount of open-source software out there that can simply be recompiled. AROS is proof positive of this - it runs on x86 AND PowerPC, and it certainly does not run the PPC in little endian mode.
Do many people really still want to run 15 year old software from an A1200? Would they buy a Netbook and want this feature?
Maybe you would. The other million customers would not give a shizzle either way.
As for the bleating about "the MorphOS guys should get a
hardware team together", what on EARTH have you been smoking lately? I recommend you stop. The MorphOS team, if they wanted to port to ARM and take control of an ARM license and develop an SoC core, can make a business case RIGHT NOW and Genesi and bplan will take in on for them. bplan have ALWAYS been around for the MorphOS team to do this kind of project. We have the contacts inside Freescale and ARM, ODMs standing by to produce millions of units.
Matt Sealey, Genesi USA, Inc.
Developer Relations
Product Development Analyst
I just wanted to point out that there's a difference between just "endianess" and "true endianess".
