2013/1/11 David Brown <david@xxxxxxxxxxxxxxx>:
> On 10/01/13 19:32, Marcin S wrote:
>> Hello,
>>
>> I have a program for ARM microcontroller (barebone STM32). Default
>> linker script puts all global const variables in .text block, which is
>> later loaded into flash memory of the cpu. Processor I am using have
>> an ability to change contents of flash on the fly, what I want to
>> achieve is to read const variable from flash, that might been changed
>> from other location of the program.
>>
>> Example
>>
>> const uint16_t SIGNATURE = 0xA1A1; //default value
>>
>> bool getSignature()
>> {
>> return SIGNATURE == 0xA1A1;
>> }
>>
>> void main(void)
>> {
>> if(getSignature())
>> {
>> printf("NOT CHANGED");
>> }else
>> {
>> printf("CHANGED");
>> }
>> }
>>
>>
>> And this works well, but only with disabled optimizations -O0,
>> however, with -O1+ it all gets "eaten" into simple printf("NOT
>> CHANGED) because variable is constant and under normal circumstances
>> result is always the same.
>> I have tried various tricks to avoid optimizing of that varaible, and
>> some are working, but I don't like it and it gives me no guarantee it
>> will work in the future.
>>
>> Is there any way to ensure this variable allocation in .text as it's
>> in source file (other then expilicitly disabling optimization for unit
>> it is defined in)?
>>
>> Marcin
>>
>
> Have you tried declaring the data as "volatile const"?
>
> mvh.,
>
> David
>
I've ended up with non-const
volatile uint16_t CFlashSignature::SIGNATURE __attribute__ ((section
(".text"))) = 0xA1A1;
definition
and so far it's optimization resistant on all levels.
Thanks for suggestion guys, that thing was bugging me for some time.
Marcin
