Re: ldrb vs ldrh in gcc-3.4.4 (ARM)

[Richard Earnshaw <rearnsha at gcc dot gnu dot org>]

On Wed, 2005-08-17 at 15:43, Steven Scholz wrote:
> Richard,
> 
> >>>First google hit on "AT91RM9200":
> >>>	http://www.atmel.com/dyn/products/product_card.asp?part_id=2983
> >>>
> >>>That page mentions that it's an ARM920T core.  First google hit on
> >>>"ARM920T":
> >>>	http://www.arm.com/products/CPUs/ARM920T.html
> >>>
> >>>That page mentions 'ARMv4T'.
> >>
> >>Thanks for googling for me! ;-)
> >>
> >>So I use either -march=armv4 _OR_ -mcpu=arm920t. Right?
> >>
> >>(Using both brought me a warning about conflicting).
> > 
> > 
> > the arm920t is an armv4t device (the 't' is thumb).
> > 
> > Basically, there are two options, -march=xxx and -mtune=xxx that are
> > independent (one selects the available instructions, the other the best
> > way to use that set for the intended cpu).  -mcpu=xxx is shorthand that
> > can be used to set both options in one go: so -mcpu=xxx is equivalent to
> > writing -march=<arch_of(xxx)> -mtune=xxx.
> > 
> > Note that to get Thumb code you have to use -mthumb; it's not sufficient
> > to tell the compiler that you have thumb instructions available.
> 
> Thanks a million. Maybe you could explain the difference of arm920t and arm9tdmi 
> as well, please?

The arm9tdmi is the main 'core' of the CPU.  The arm920t is the core
plus the associated cache, mmu, and system registers.   Different models
all have substantially the same 'core' but may have different (or
missing) additional parts.  Thus arm920t arm926t arm966t etc.

It's not quite as simple as that (for marketing reasons), but that's the
one paragraph summary.

See the ARM web site for more details of the different products
(www.arm.com).

R.

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