How to store additional code sections in FLASH memory (AVR, GCC)

0
votes

I am working with AVR ATmega328p MCU and I would like to add constant string at address 0x7000 into flash memory. How can I do this with AVR-GCC?

My code contains this declaration:

// Firmware version
static volatile char version[16] __attribute__ ((section (".fwversion"))) = "0.01 DEV";

Now, when I run gcc with this flags:

avr-gcc -Wl,--section-start=.fwversion=0x7000 -mmcu=atmega328p -DF_CPU=8000000UL -Os -Wall -o main.elf main.c

The ELF file contains section .fwversion and after avr-objcopy, there are data at address 0x7000 in iHEX file.

But when I run gcc with -Wl,--gc-sections flag:

avr-g++ -Wl,--gc-sections -Wl,--section-start=.fwversion=0x7000 -mmcu=atmega328p -DF_CPU=8000000UL -Os -Wall -o main.elf main.c

the .fwversion section is removed.

I need to use -Wl,--gc-sections flag but I also need constant string stored in flash memory. What flags should I use to achieve this?

Is it possible to use something like this in GCC?

static volatile char version[16] __attribute__ ((section (0x7000))) = "0.01 DEV";
2
linkeravr-gccatmega
Are you saying that avr-objdump doesn't show the .fwversion section in main.elf? - Ignacio Vazquez-Abrams
Yes, .fwversion is removed in ELF, thus the code is not in HEX file. - vasco
There are reasons why it would not be in the HEX, separate of whether or not it's in the ELF. - Ignacio Vazquez-Abrams

2 Answers

0
votes

I am unsure why it needs to be at that certain address unless you want it available for the bootloader.

This Program Memory link discusses the functions that are available for storing and accessing flash memory from locations. Typically you store and access strings in flash memory by using the PSTR command. E.g.

char str[16] = PSTR("I am a string\n");
0
votes

I think static volatile char is just not the thing you mean. Maybe const char, like this:

const char version[16] __attribute__ ((section(".fwversion"))) = "0.01 DEV";

Also notice memcpy_PF function.