Create an Application

A general application for a KNoT Thing has the following structure:

<app-name>/
 ├── CMakeLists.txt
 ├── prj.conf
 ├── setup.conf
 ├── <board>.overlay (optional)
 └── src/
     └── <app-name>.c

Let’s see what each file does.

CMakeLists.txt

CMakeLists.txt is a configuration file for CMake. It contains a set of directives and instructions describing the project’s source files and targets.

Below you can see a CMakeLists.txt from a simple KNoT project.

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cmake_minimum_required(VERSION 3.8.2)

if (NOT DEFINED ENV{KNOT_BASE})
   message(FATAL_ERROR "Source the KNoT shell initialize script!")
endif()

include($ENV{KNOT_BASE}/core/CMakeLists.txt)
project(<app-name>)

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})

You must change the <app-name> for your project name on line 8.

prj.conf

The prj.conf file is a configuration file that contains information about KNoT Zephyr project.

The name of the Device, the number of sensors/actuators the device has, logging configuration and sensors/actuators configuration are placed in this file.

Below you can see a prj.conf from a simple KNoT project.

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# KNoT
CONFIG_KNOT_NAME="<device-name>>"
CONFIG_KNOT_THING_DATA_MAX=1

# Logging
CONFIG_LOG=y
CONFIG_LOG_IMMEDIATE=n
CONFIG_KNOT_LOG=y
CONFIG_KNOT_LOG_LEVEL_DEBUG=y
CONFIG_LOG_PRINTK=y

Change the name of your device (line 2) and the maximum number of sensors you are using (line 3).

Note

The CONFIG_PRINTK option may not work as expected on KNoT Dongle. You still can use the CONFIG_LOG_PRINTK with all supported boards.

setup.conf

setup.conf is a configuration file tha contains information about bluetooth configuration.

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CONFIG_BT_DEVICE_NAME="BLE device name"

Change the name of bluetooth advertise name (line 1).

<board>.overlay (optional)

It is possible to use a DTS overlay file on the project by adding a file named <board>.overlay and placing it on the application main directory.

src/<app-name>.c

The <app-name>.c contains the application main code.

It is structured by two basic functions, setup() and loop().

You can see a start code example bellow.

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#include <zephyr.h>
#include <net/net_core.h>
#include <logging/log.h>
#include <device.h>
#include <gpio.h>

#include "knot.h"
#include <knot/knot_types.h>
#include <knot/knot_protocol.h>

void setup(void)
{

}

void loop(void)
{

}

Use loop() function to include your application logic.

Warning

loop() function must NOT be blocking.

Use setup() to register your sensors/actuators using knot_data_register() and configure which events should send data to cloud with knot_data_config().

For each registered sensor/actuator you may want to create a write_cb or read_cb function, which will be passed as callbacks on register function.

Example (blink):

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void setup(void)
{
   /* Peripherals control */
   gpio_led = device_get_binding(LED_PORT);
   gpio_pin_configure(gpio_led, LED_PIN, GPIO_DIR_OUT);

   /* KNoT config */
   knot_data_register(0, "LED", KNOT_TYPE_ID_SWITCH,
            KNOT_VALUE_TYPE_BOOL, KNOT_UNIT_NOT_APPLICABLE,
            &led, sizeof(led),
            write_led, read_led);

   knot_data_config(0, KNOT_EVT_FLAG_CHANGE, NULL);

}

In this example a LED Sensor is registered with:

  • id = 0;

  • name = LED;

  • type_id = KNOT_TYPE_ID_SWITCH;

  • value_type = KNOT_VALUE_TYPE_BOOL;

  • unit = KNOT_UNIT_NOT_APPLICABLE;

  • variable_address = &led;

  • variable_size = sizeof(led);

  • write_cb = write_led;

  • read_cb = NULL;

And it is configured to send message to Cloud every time the value changes.

  • write_cb: This function is used to write in the actuator the value of the associated variable. It is executed after the variable value is updated remotely.

  • read_cb: This function is used to write the value read from the sensor into the variable. It is executed in polling.

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int write_led(int id)
{
   gpio_pin_write(gpio_led, LED_PIN, !led); /* Led is On at LOW */

   return KNOT_CALLBACK_SUCCESS;
}