LPC2103 - GCC (Winarm) - Crashes when using Thumb Interwork

John Dominey wrote:
> Hi,
> I'm developing an application in C for the NXP LPC2103 which uses
> interrupts (VIC) and works fine using just ARM code. However I'm almost
> out of code space and am trying to use THUMB. Enabling -mthumb-interwork
> (rather than -mno-thumb-interwork), without even building a file in
> THUMB, causes the processor to hang when it encounters an interrupt. Not
> enabling interrupts at startup cures this problem, but the application
> relies on them heavily. Optimisation is -0s (size), the program won't
> fit in any other mode.
>
> My interrupt enabling/disabling routines are:
>
> inline unsigned enableIRQ(void)
> {
>   unsigned _cpsr;
>
>   _cpsr = asm_get_cpsr();
>   asm_set_cpsr(_cpsr & ~IRQ_MASK);
>   return _cpsr;
> }
>
> inline unsigned disableIRQ(void)
> {
>   unsigned _cpsr;
>
>   _cpsr = asm_get_cpsr();
>   asm_set_cpsr(_cpsr | IRQ_MASK);
>   return _cpsr;
> }
>
> I think it's the actual getting into/out of the ISRs which is causing it
> to fall over.
>
> I'm using the latest version of Winarm (20060606). I've tried using
> Yagarto as well, with exactly the same problem.
>
> Can anyone suggest what's going wrong? I've been trying to get to the
> bottom of this for a while, and it's now getting urgent!
>
> P.S. I'm not very familiar with ARM assembly yet.
>
> Thanks, John.

There is a known problem with interwork, interrupts and optimization. It
has been discussed in in different forums/mailing-lists. A rather easy
approach to work around this is to declare the functions with the
"nacked" attribute and use entry- and exit-macros. It's not elegant or
portable but works. The example lpc2106_uart_irq (based on code from
Bill Knight) demonstrates this method. Another appraoch is an
assembler-wrapper, for LPC it's demonstrated in the gcc-port of the
LPC213x/4x driver-examples available in WinARM (update versions on my
web-pages). Also see the various gcc-Ports of AT91SAM7 examples, the
wrapper can be included easily, no knowledge in ARM assembly needed.

Martin Thomas

Thanks - it works!!!!
I'm not sure what to do about the exception handlers like

void SWI_Routine   (void)  _attribute_ ((interrupt("SWI")));
void UNDEF_Routine (void)  _attribute_ ((interrupt("UNDEF")));

How do you make these "nacked" while still telling the compiler that
they're SWI and UNDEF interrupts? Do you still need to use ISR_ENTRY()
and ISR_EXIT()?
I know these interrupts should never be encountered, and I intend to
reset the  processor when they are, but how should it be done?

Thanks again,
John