[ECOS] Cortex M3 idle sleep

Nick Garnett nickg@ecoscentric.com
Fri Feb 13 16:08:00 GMT 2009


Simon Kallweit <simon.kallweit@intefo.ch> writes:

> Hello
> 
> Would it make sense to include support for sleeping ("wfi"
> instruction) in idle thread for the cortex m3 architecture? The
> current code in hal_arch.h looks like:
> 
> #if 0 //ndef HAL_IDLE_THREAD_ACTION
> #define HAL_IDLE_THREAD_ACTION(__count) __asm__ volatile ( "wfi\n" )
> #else
> #define HAL_IDLE_THREAD_ACTION(__count) CYG_EMPTY_STATEMENT
> #endif
> 
> I guess this is not what it was meant to be. I would propose to add an option like CYGHWR_HAL_CORTEXM_IDLE_SLEEP to enable the wfi instruction:
> 
> #ifndef HAL_IDLE_THREAD_ACTION
> # ifdef CYGHWR_HAL_CORTEXM_IDLE_SLEEP
> #  define HAL_IDLE_THREAD_ACTION(__count) __asm__ volatile ( "wfi\n" )
> # else
> #  define HAL_IDLE_THREAD_ACTION(__count) CYG_EMPTY_STATEMENT
> # endif
> #endif
> 
> Also, currently var_arch.h gets not included in the hal_arch.h header, so it's impossible to override for example the HAL_IDLE_THREAD_ACTION macro. I guess this was just overlooked, or is it intentional?
> 
> I can provide a patch if there are no objections.


The "#if 0" is an oversight on my part. When debugging via JTAG I was
having difficulties breaking in to an idle system. Stopping it using
WFI solved this. The #else part is also a consequence of this, so that
code should really be:

#ifndef HAL_IDLE_THREAD_ACTION
#define HAL_IDLE_THREAD_ACTION(__count) __asm__ volatile ( "wfi\n" )
#endif

Given this I don't really see any need for the
CYGHWR_HAL_CORTEXM_IDLE_SLEEP option. If a variant or platform HAL
needs to override this it can very easily by redefining
HAL_IDLE_THREAD_ACTION().

var_arch.h should certainly be included in hal_arch.h. It is only
because the STM32 has an empty var_arch.h that we haven't noticed this
before.


-- 
Nick Garnett                                        eCos Kernel Architect
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