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Parameters

GrowNode allows users to access Leaves input and outputs through Parameters. A parameter defines its behavior and holds its value. Depending on their configuration, parameters can be exposed and accessed from inside the code (eg. from an onboard temperature controller) or from the network (eg. to monitor the water level). They can be also updated in both ways.

Parameters can be stored in the NVS flash (the ESP32 'hard drive') in order to be persisted over board restart, in a transparent way (no code needed).

Initialization

Each Leaf has a predetermined set of parameters. Those are initialized in the configuration phase described in the Leaves section. However, the initial values can be overridden by the user. For instance, a parameter defining a GPIO pin should be customized depending on the board circuit. To do this, the gn_leaf_param_init_XXX() functions are defined. Example: 

    gn_leaf_handle_t lights = gn_leaf_create(node, "light switch", gn_gpio_config, 4096);
    gn_leaf_param_init_double(lights, GN_GPIO_PARAM_GPIO, 25);

Here, a lights leaf is created using the gn_gpio_config callback. This leaf (see gn_gpio leaf code) has a parameter called GN_GPIO_PARAM_GPIO that represents the GPIO to control. This code assigns the value 25 to that parameter at startup.

Overwrite stored parameters

A leaf parameter can be stored in the board flash depending on its configuration. Standard behavior is that on next startup the init function will be ignored.

This could be overridden by using the gn_leaf_param_force_XXX() instead. this will set the parameter at the desired value ignoring the previously set value.

Fast creation

Some leaves has convenient functions created to perform creation and initialization in a compact form. Those functions have the suffix _fastcreate (see for instance gn_gpio_fastcreate() on gn_gpio.c leaf)

Update

A leaf parameter can be updated:

When updating from user code, the gn_leaf_param_set_XXX() functions are used. They inform the leaf that the parameter shall be changed to a new value. This is done via event passing as the leaf resides to another task, so it's an asynchronous call.

Code Sample: Leaf declaration and parameters initialization

This is the complete code to create and configure a BME280 Leaf sensor, a temperature + humidity + pressure sensor (for complete description of this sensor, see leaves

    gn_leaf_handle_t env_thp = gn_leaf_create(node, "bme280", gn_bme280_config, 8192);
    gn_leaf_param_init_double(env_thp, GN_BME280_PARAM_SDA, 21);
    gn_leaf_param_init_double(env_thp, GN_BME280_PARAM_SCL, 22);
    gn_leaf_param_init_bool(env_thp, GN_BME280_PARAM_ACTIVE, true);
    gn_leaf_param_init_double(env_thp, GN_BME280_PARAM_UPDATE_TIME_SEC, 10);