Subject: Re: Building for both ARM V4 and ARM V5 systems
To: Richard Earnshaw <Richard.Earnshaw@buzzard.freeserve.co.uk>
From: David Laight <email@example.com>
Date: 08/06/2006 21:47:40
On Sat, Aug 05, 2006 at 02:04:42AM +0100, Richard Earnshaw wrote:
> > volatile ushort ptr = /* WHATEVER THE DEVICE ADDRESS is MAPPED to */
> > ushort value;
> > *ptr = value; /* If you want to store to the device */
> > value = *ptr; /* If you want to read from it. */
> > The problem is that the compiler generates two byte operations for
> > such a reference, rather than one half word operation, for V4.
> Nonsense. ARMv4 has half-word operations and if you use -march=armv4 the
> compiler will use them.
But, IIRC, that range of offsets is less for the half-word operations,
and gcc is likely to use 32bit operations to read 16bit values (masking
the high bits). Even using misaligned transfers for 4n+2 addresses.
(or do we disable that in netbsd's versions of gcc?)
David Laight: firstname.lastname@example.org