Reading/Writing to Axon II's eeprom

[BANE]

Hello all,
just try to get my feet wet with reading/writing to my Axon II's eeprom.  Ive read all of webbots info (not sure if i understand it all yet, but hopefully will) and im getting some warning from AVR studio.

here is just the parts of code involving eeprom

Code: [Select]

//eeprom store var
int x_max_position;
//write to eeprom
x_max_position=10;
eeprom_write_byte(x_max_position, left_joy_x_max);
//display
rprintf("XMP=%d",eeprom_read_byte(x_max_position));
it gives me a warning saying:

warning: passing argument 1 of 'eeprom_write_byte' makes pointer from integer without a cast

also, returns the value 0, not 10

I read about having to include "EEMEM" in the variable but the compiler doesnt like it    
Can anybody see my error?  probably syntax error
thanks,

[Webbot]

You definitely need the EEMEM in the variable definition.
If the compiler doesn't like it then you probably dont have

Code: [Select]

#include <avr/eeprom.h>

[BANE]

Ok, ive include that avr/eeprom but I still dont understand how to include EEMEM in the variables definition

Code: [Select]

uint8_t EEMEM x_max_position;  AVR studio says

error: section attribute cannot be specified for local variables

here is the new code:

Code: [Select]

#include <avr/eeprom.h>

uint8_t EEMEM x_max_position;

eeprom_write_byte(x_max_position, 10);

rprintf("XMP=%d",eeprom_read_byte(x_max_position));

[Webbot]

I'm guessing that you are trying to do it wit a variable that is defined inside a function - which is a no no. It must be a global variable.
ie

Code: [Select]

#include <avr/eeprom.h>

uint8_t EEMEM globalVar; // Should be ok

void foobar(void){
    uint8_t EEMEM localVar; // Probably gives your error and cannot work
}
The difference is that 'globalVar' will always exist at the same memory location whereas 'localVar' comes and goes and is only valid whilst 'foobar' is running so can have a different memory slot every time its called.

[BANE]

ahhh i now know that global variables are

However, im still getting the two same warnings and every time i read and i get 255 not 10

Code: [Select]

#include <avr/eeprom.h>
uint8_t EEMEM x_max_position;

TICK_COUNT appControl(LOOP_COUNT loopCount, TICK_COUNT loopStart) {
eeprom_write_byte(x_max_position, 10);
rprintf("LJM=%d",eeprom_read_byte(x_max_position));

return 0;
Can i use x_max_position like this inside TICK_COUNT?
}

[Webbot]

when you compile your program you will be getting warning errors like this:

Code: [Select]

warning: passing argument 1 of '__eewr_byte_m640' makes pointer from integer without a cast
This is because you should be passing the address of your variable - not the contents of the variable - ie it should be prefixed with an '&' symbol. So try changing your code to this:-

Code: [Select]

#include <avr/eeprom.h>
uint8_t EEMEM x_max_position;

TICK_COUNT appControl(LOOP_COUNT loopCount, TICK_COUNT loopStart) {
eeprom_write_byte(&x_max_position, 10);
rprintf("LJM=%d",eeprom_read_byte(&x_max_position));

return 0;
C is a real pain with this stuff - and its made worse by the avr-gcc compiler just issuing them as warnings rather than errors.

[BANE]

yep that little "&" made all the difference

helpful+1

thanks a ton

[waltr]

This is because you should be passing the address of your variable - not the contents of the variable - ie it should be prefixed with an '&' symbol.

Yep, this is called a 'pointer'.
For a better understanding see the K&R C book.
http://en.wikipedia.org/wiki/The_C_Programming_Language
http://www.amazon.com/Programming-Language-2nd-Brian-Kernighan/dp/0131103628