Re: [avr-gcc-list] storing values at a spcified location in FLASH..?

[E. Weddington]

Eivind Sivertsen wrote:

> Hi guys,
>
>  
Hi Eivind!

Are things calming down now for you? :-)

> I am looking for a way to store values at specified locations in flash, for
> instance calibration values, serial number...etc...
> I know that other compilers may use preprocessor directives to do this, but
> I cant find the combination that does the trick with WinAVR...
> The solution below seems to just add the data at the flash location wherever
> code ends.
>
> Suggestions?
> Cheers,
>
> Eivind
>
>
> //
> // Test for defining location of var in flash
> //
> // 1. Declare the array as below
> //
> // 2. Add the following link flags:
> // -Wl,--section-start=.calib=0x100,--cref
> //
> // 3. Generate Intel Hex file using avr-objcopy
> // Use the following flags:
> // -j .text -j .data -j .calib
> //
>
> #include <avr/io.h>
> #include <avr/pgmspace.h>
>
> const unsigned char calval[] __attribute__ ((section (".calib"))) = {0xcd,
> 0xce};
>
> int main(void){
> unsigned char *calvalP;
>
> calvalP = calval;
>
> }// end
>
>  
Actually you're very close.

Your declaration of calval with the attribute is correct.

You need to change your main() code to below:

int main(void)
{
   unsigned char mem_calval[2];

   mem_calval[0] = (unsigned char)pgm_read_byte(&(calval[0]));
   mem_calval[1] = (unsigned char)pgm_read_byte(&(calval[1]));

}

Remember that you are putting calval into the Program Memory, so the 
only way to read the value from there is to use the Program Space 
routines such as pgm_read_byte(). The argument is the *program space 
address* that you are reading from, hence: &(calval[0]). Technically you 
can also use pgm_read_word() to read out a word value. You can also use 
memcpy_P() to copy any size block of data from Program Memory to a 
RAM-based buffer.

I *highly* recommend that you use the WinAVR Makefile template (or 
MFile). That way you don't have to be concerned about the commands to 
generate the hex file.

Put this line in your Makefile, after the group of LDFLAGS variable 
settings:
LDFLAGS += -Wl,--section-start=.calib=0x100
Of course, change your address to the one desired.

After you build your software, open up the .map file and you can see the 
.calib section at the correct address. Then open up the .hex file and 
you can even see the correct values at the correct address.

HTH
Eric

PS. Many thanks to you and Erlend for getting the Freaks website back up!