Flash memory acces and floats

Forum 2005-2010 (read only) Software Syntax & Programs
1

Hi everyone,

can someone help me to write and read data to/from flash memory?
I have tried to save two arrays into programspace, but my code won't compile. Do I have to declare the datatype again when I want to write to the array?
Also, can floating point numbers be stored in flash memory?

Thanks a lot for your help!

#include <stdio.h>
#include <math.h>
#include <avr/pgmspace.h>

int PROGMEM SensP[3];
int PROGMEM OffsetP[3];
float Sens[3] = {0}, Offset[3] = {0};

//in the loop:

for(int i = 0; i < 3; i++){
OffsetP PROGMEM = (int)round(Offset*);*
SensP PROGMEM = (int)round(Sens*);*
* }*

2

Generally speaking data compiled into flash memory is constant and cannot be written to at runtime unless you happen to be a bootloader.

3

me again,

I removed the declaration with global scope and put just this in the local scope:

prog_int16_t OffsetP[3] = myInteger;

and it compiled.

How can I access and read this array after restarting the arduino?

4

Hi Andy,
thanks for your reply. I need to store some calibration data in non.volatile memory. The reference section says:

"Data in Program Space PROGMEM
Store data in flash (program) memory instead of SRAM. There's a description of the various types of memory available on an Arduino board.... " and it describes how to store data there.

I tried the above code and it compiles all right.

So I don't exactly understand what you mean. Would you mind explaining me in more detail ?

5

I can do one better. Storing the calibration data in EEPROM is a much better choice.

6

It looks like you are still trying to write to flash at runtime. You can't do that, you can only access constants. e.g. data declared at global scope like this:

#include <avr/pgmspace.h>

prog_int16_t myProgArray[] PROGMEM={ 0,1,2,3 };

May be read in your code at runtime like this:

for(int i=0;i<=3;i++)
{
  int16_t myProgInt=pgm_read_word(&myProgArray[i]);
}

...and yes, CodingBadly's suggestion to use EEPROM for persistent data that will change at runtime is the best option.

7

Hi Andy,

I understand what you mean. So the programspace can only be written to when the program is uploaded.

Is there any way to store data at runtime to non-volatile memory at all?

How could I store and retrieve the calibration data?

8

Is there any way to store data at runtime to non-volatile memory at all?

Yes. That's what EEPROM is for. Here, take this clue by four, and whack yourself a couple of times.

9

A good place to start reading would be the EEPROM tutorials in the Arduino playground. Here's a link:

10

thanks for your answers!
I am still new to arduino and programming.
I will store the data in Eeprom.