Re: [avr-gcc-list] How to define a ROM data in a perticular address?

[Erik Christiansen]

On Mon, Apr 24, 2006 at 06:23:04PM +0530, Ruwan Jayanetti wrote:
> I need to define some data in a particular address in ROM (flash). Any
> idea how can I do this?
> 
> I tried including an assembler file:
> 
> .org 0x80
> 
>  .byte 0xaa
>  .byte 0x55
> 
> But compiler / linker don't seems to care about .org directive. The
> bytes are getting in with other program strings defined in C, but
> leaving a gap of 0x80.

Hi Ruwan,

The linker script is very convenient for managing an embedded system's
memory map. You can replace the .org with:

   .section .elephant,"a"

Then, in the linker script:

SECTIONS
{
   ...

   .elephant : AT (0x12345) { *(.elephant) } > text

}

Where 0x12345 is your preferred flash address. You can also use
e.g. "AT (62K)"

You can also add global labels to the assembler source:

   .global message

   .section .elephant,"a"
message:
   .asciz "Hello World"

Remember to use the avr-gcc option -T to specify your modified linker
script. There are several for each avr family, in
/usr/local/avr/avr/lib/ldscripts/avr. (Or vicinity)

As I understand it, it'll also be necessary to employ the progmem
functions if you need to access the data in C, unless your own assembler
access functions are provided.

hth,
Erik