NCS settings subsystem loading order

[db_lw]

Hello everyone,

I'm using the NCS/Zephyr settings subsystem to store some application data in non-volatile memory.

The settings structure looks something like this:

app/peripherals
app/config/0

I use the SETTINGS_STATIC_HANDLER_DEFINE to register two set-functions one for <app/peripherals> and one for <app/config>. I would like to have the <app/peripherals> settings before the other stuff but the set-function for <app/config> is always called before the other one.

I was wondering if I could affect the order in which the set-functions are called?

Thanks in advance!

[ovrebekk]

Hi 

Have you tried to change the order of your calls to settings_register() to see if it changes the order in which the set functions are called?

If this doesn't work I will check with the software developers if there is some way to influence this. 

Best regards
Torbjørn

[db_lw]

Hello Torbjørn,

at the moment I don't use the settings_register() function, instead I use the SETTINGS_STATIC_HANDLER_DEFINE() because I don't need the dynamic handler. If I change the order of this macro calls it doesn't influence the settings read order.

Best regards,
David

[ovrebekk]

Hi David

Apparently there is no API to set the order explicitly, but they are organized alphabetically by the handler name. 

In other words you can influence the order by adding a prefix to the handler name, something like this:

aa_first_handler
ab_second_handler

Best regards
Torbjørn

[db_lw]

I can't get it to work, that the settings are read in the order i want.

Here is a basic example that I tried:

static int alpha_handle_set(const char *key, size_t len_rd,
			settings_read_cb read_cb, void *cb_arg)
{
    LOG_INF("ALPHA");

    return 0;
}


SETTINGS_STATIC_HANDLER_DEFINE(alpha_handler, "alpha", NULL, alpha_handle_set,
			       NULL, NULL);

static int beta_handle_set(const char *key, size_t len_rd,
			settings_read_cb read_cb, void *cb_arg)
{
    LOG_INF("BETA");

    return 0;
}

SETTINGS_STATIC_HANDLER_DEFINE(beta_handler, "beta", NULL, beta_handle_set,
			       NULL, NULL);

static int store_settings(void)
{
    int err;
    static uint32_t value[] = {0xAAAAAAAA, 0xBBBBBBBB};
    const char alpha[] = "alpha";
    const char beta[] = "beta";
    const char *key[] = {alpha, beta};

    for (uint8_t i = 0; i < ARRAY_SIZE(value); i++) {       // VARIANT 1 (Save alpha first)
    //for (int8_t i = ARRAY_SIZE(value) - 1; i >= 0; i--) { // VARIANT 2 (Save beta first)
        err = settings_save_one(key[i], &value[i], sizeof(value[i]));
        if (err) {
            LOG_ERR("Couldn't save %s", key[i]);
            return err;
        }
    }

    return 0;
}

When I use this code it doesn't matter how I name the handlers but the order how I write the settings entries is relevant. If I write alpha and then beta the beta handler is always called first and if I write beta and then alpha the alpha handler is called first.

ovrebekk said:

In other words you can influence the order by adding a prefix to the handler name, something like this:

aa_first_handler
ab_second_handler

In my case the alpha_handler should always be called before the beta_handler am I right?

Best regards,
David

[ovrebekk]

Hi David

You mean to say the order at which you call the SETTINGS_STATIC_HANDLER_DEFINE macros decide which of the set functions is run first?

db_lw said:

In my case the alpha_handler should always be called before the beta_handler am I right?

That was my expectation, yes, but based on your findings this might not be the case. 

Best regards
Torbjørn

[db_lw]

ovrebekk said:

You mean to say the order at which you call the SETTINGS_STATIC_HANDLER_DEFINE macros decide which of the set functions is run first?

No, I mean the order in which I store the settings decides which of the set functions is run first.

It seems like it doesn't matter what I do with SETTINGS_STATIC_HANDLER_DEFINE macro. I tried the following things:

• Change the order of the SETTINGS_STATIC_HANDLER_DEFINE macro calls.
• Change the handler names to aa_handler and ab_handler.
• Change the key strings.

Nothing of those things changed the order in which the set functions are run.

Best regards,
David