Re: [arm-gnu] Thumb mode

[Kishore <kitts.mailinglists@xxxxxxxxx>]

On Friday 22 Jan 2010 5:15:37 am Charles Manning wrote:
> On Thursday 21 January 2010 04:45:10 Kishore wrote:
> > Is there any way of informing the compiler to compile ISR's in ARM mode?
> > The way i currently know is by compiling the file that contains the ISR
> > without the -mthumb compiler option.
> > 
> > The problem i have is that my build system puts in the -mthumb option
> > globally and i override that with -marm option for files containing the
> > ISR's. However, I would curious to know if there is another method like a
> > function attribute to the same effect.
> 
> While Carlos has given you adequate answer, it leaves me wondering why
> you'd want to do this.
> 
> While ARM  mode is faster on some devices that is not true for all devices.

Actually, i have not yet concluded that I want to run in thumb mode. I had 
read recently that thumb mode results in smaller and faster code on some 
processors and so i wanted to try it. First i wanted to test whether my 
program works fully when compiled in thumb. I am happy to say that i observed 
no change in functioning of my program when compiled in thumb mode.

Now for the performance front. I am still evaluating this. There is a ~35% 
size reduction. I am not pressed for size as i have a AT91SAM7S256 with 256 KB 
of flash and even in ARM mode I am consuming only about 90 KB (Release mode O3, 
O2 results in smaller but slower code). I am really interested on the speed 
front that I am yet to test. Does anyone have any comments on this?
-- 
Cheers!
Kishore