Re: Allocating code to separate sections

On 2014/10/09 08:29 AM, Senthil Kumar Selvaraj wrote:
> On Thu, Oct 09, 2014 at 07:32:51AM +0200, Alistair Gadd wrote:
>> Hi Everybody,
>>
>> I'm hoping this is an easy one for someone out there.
>>
>> I'm putting together a bootloader for an ATmega328P using Atmel Studio 6.2
>> and I would just like to ask if there is an easy way configure the IDE so
>> that I can have separate sections that I can allocate code to. I have been
>> using "-Ttext 0x7000" as a linker flag in "Configuration
>> Manager->Toolchain->AVR/GNU Linker->Miscellaneous", which places all the
>> code starting with reset vector at 0x3800 onwards, but I would like to have
>> another section in the application section where I can place an SD card
>> library that will be accessible by the bootloader and by future
>> applications.
>>
>> I have defined another "FLASH segment" - ".sdlib=0x2000" in "Configuration
>> Manager->Toolchain->AVR/GNU Linker->Memory Settings, but I don't know how to
>> configure .c source files and assembler .s files so that their code is
>> allocated to this segment.
>>
>> Can anybody give me some ideas on how I could achieve this?
> There are a couple of ways.
>
> 1. Create a linker script that groups code from specific object
> files into custom output sections. Something like
>
> .sdlib :
> {
>      foo.o(*.text)
> }
>
> where foo.o is the object file containing the code to go into the
> section.
>
> 2. Use attributes in C code and .section directives in assembler code to
> specify the section.
>
> void __attribute__((section(".sdlib"))) my_function() {}
> int main() { return 0; }
>
> This makes the place the my_function's code in a .sdlib section. main's
> code still goes into .text.
>
> Hope this helps.
>
> Regards
> Senthil
Thanks very much Senthil,

I have tried the __attribute__((section(".sdlib"))) directive which 
works but I'm having problems trying to define variables in flash by using:

const unsigned char __attribute__((section(".sdlib"))) array[5] PROGMEM  
= {1,2,3,4,5};
or:
const unsigned char array[5] __attribute__((section(".sdlib"))) PROGMEM  
= {1,2,3,4,5};

I think I prefer your first option though because it would put 
everything in that module into the .sdlib section, but my problem is I 
don't know how to create and use the linker script. Can you maybe point 
me to some documentation that would show me how it is used.

Best regards,
Alistair.



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