How to save uint32_t variable to a specific address in flash memory in nrf connect sdk?

[Nikolay Oleynik]

Hello. How to save uint32_t variable to a specific address in flash memory in nrf connect sdk? in other projects this was solved by allocating a custom flash memory section in the linker script, and also using __attribute__((section("name"))). But in zephyr the linker script is generated during assembly. If it's not difficult, give an example of how to implement this, thanks in advance

[donnagodwin]

Hello,

In the NRF Connect SDK, you can save a uint32_t variable to a specific address in flash memory by using the Flash Storage API provided by the Zephyr RTOS. Here's an example of how you can implement this:

1. Define the custom flash section and symbol in your application's prj.conf file:

CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_CUSTOM_FLASH_SECTION=y
CONFIG_CUSTOM_FLASH_SYMBOL="__custom_flash"

2. Create a custom linker script for your application. Create a file named custom.ld in your project directory and add the following contents:

SECTIONS {
.custom_flash_section :
{
KEEP(*(.__custom_flash))
} > flash
}

3. Update your CMakeLists.txt file to include the custom linker script. Add the following line:

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set(DTC_OVERLAY_FILE ${CMAKE_CURRENT_SOURCE_DIR}/custom.ld)

4. In your source code, declare and define your uint32_t variable and place it in the custom flash section using the __attribute__((section("name"))) attribute:

c

#include <zephyr.h>
#include <device.h>
#include <drivers/flash.h>

__attribute__((section(".custom_flash_section")))
uint32_t my_variable = 42;

5. To save the variable to flash memory, use the Flash Storage API provided by Zephyr. Here's an example of how you can do this:

c

#include <zephyr.h>
#include <device.h>
#include <drivers/flash.h>

void save_variable_to_flash(void)
{
const struct device *flash_dev;
int err;

flash_dev = device_get_binding(DT_CHOSEN_ZEPHYR_FLASH_CONTROLLER_LABEL);
if (!flash_dev) {
printk("Flash device not found\n");
return;
}

uint32_t flash_address = (uint32_t)&my_variable;

err = flash_write_protection_set(flash_dev, false);
if (err) {
printk("Failed to disable flash write protection\n");
return;
}

err = flash_write(flash_dev, flash_address, &my_variable, sizeof(my_variable));
if (err) {
printk("Failed to write variable to flash\n");
return;
}

err = flash_write_protection_set(flash_dev, true);
if (err) {
printk("Failed to enable flash write protection\n");
return;
}

printk("Variable saved to flash\n");
}

Make sure to adjust DT_CHOSEN_ZEPHYR_FLASH_CONTROLLER_LABEL to match the label of the flash controller in your device tree.

[Nikolay Oleynik]

Hello, thanks for the answer, I'll definitely try it. I need to save a variable as a constant when compiling. Will this method work with a const specification?