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Re: [Qemu-devel] Missing ARMv6 instructions?

From: Lennert Buytenhek
Subject: Re: [Qemu-devel] Missing ARMv6 instructions?
Date: Thu, 30 Mar 2006 17:25:24 +0200
User-agent: Mutt/1.4.1i

On Thu, Mar 30, 2006 at 03:30:30PM +0100, Jamie Lokier wrote:

> I wonder about patents (and their validity).
> A MIPS hardware implementation that I worked with had all the basic
> MIPS integer instructions except one small group, on the ground that
> those instructions were covered by a MIPS patent and so they dared not
> include it.  It was the instruction used for unaligned memory word
> access.  For that reason, we used a modified GCC specially for that
> chip.

Note that the new ARM ABI being pushed by ARM ltd, which is called
EABI, mandates using a thumb-related instruction (bx) in the function
exit path.

In other words, if the arm-compatible core that you wrote for your
FPGA board to play with does not implement that instruction (possibly
because you want to avoid infringing on ARM patents), you won't be
able to run any EABI-using ARM distros on it.  


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