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Re: Harvard architecture with 24 bit data bytes and 32 bit code bytes
- From: Ian Lance Taylor <iant at google dot com>
- To: Ned <Thomas dot Gill at csr dot com>
- Cc: binutils at sourceware dot org
- Date: 27 Feb 2008 08:55:23 -0800
- Subject: Re: Harvard architecture with 24 bit data bytes and 32 bit code bytes
- References: <op.t66zf1jj34duuh@tg01pc02.europe.root.pri>
Ned <Thomas.Gill@csr.com> writes:
> I'm beginning to hack a binutils port for our in-house DSP core. It's
> a Harvard architecture, with different sized bytes in instruction and
> data memory. Instruction memory has a smallest addressable unit of 32
> bits, while data memory has a smallest addressable unit of 24 bits.
>
> Does anyone on the list know whether this is going to cause me a lot
> of pain? Has anyone had to deal with this problem before?
>
> I'm guessing my first problem will be that there's only one
> OCTETS_PER_BYTE. I'll presumably have to look at the places where
> that's used and add code to guess whether it should be using 3 or
> 4. Is there likely to be anything else that trips me up? Any corner
> cases I should watch out for?
I find it much simpler to avoid the OCTETS_PER_BYTE code and just use
byte addressing for everything. You compensate in the relocation
processing, which is the only place which really cares.
Ian