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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