Adding Sensors with SAPI

Itron's Sensor API handles all details of creating a CoAP resource URI for your sensors, and making sensor data available over Itron networks using Milli and CoAP.  To add sensors to your Milli reference application code with SAPI, developers need to:

1. Initialize the sensor
2. Register the sensor with SAPI
3. Provide function for reading sensor data
4. If the sensor is configurable, provide functions for reading and writing sensor configuration

Example C code for these steps is provided below.

Sketch Code to Add Sensors

#include <Arduino.h>
#include "sapi_mshield.h"
#include "sapi_error.h"
#include "sapi.h"
#include "TempSensor.h"

static uint8_t temp_sensor_id;

//
//  Arduino setup function.
//
void setup()
{
    sapi_error_t rcode;
    
    // Initialize Sensor API
    sapi_initialize(NULL);
    
    // Register temp sensor
    temp_sensor_id = sapi_register_sensor(TEMP_SENSOR_TYPE, temp_init_sensor, temp_read_sensor, temp_read_cfg, temp_write_cfg, 1, 180);
    
    // Initialize temp sensor
    rcode = sapi_init_sensor(temp_sensor_id);
           
}

//
// Arduino main loop function.
//
void loop()
{
    // Call SAPI run to do the heavy lifting
    sapi_run();
}

Sensor Implementation

Typically developers will separate sensor implementation into dedicated header and source files, for example TempSensor.h and TempSensor.c.  The sensor implementation includes an initialization function that performs any initialization tasks needed on startup, before the sensor is registered with SAPI and available to provide data.  Initial configuration, setting a default value or performing an initial sensor read, and logging are typical implementation steps a developer would provide in the initialization function.  The prototype for this function is sapi_error_t sensor_init_function_name().

For each sensor, a read function must be supplied.  The prototype for the read function is sapi_error_t sensor_read_function(char *payload, uint8_t *len).  The sensor reading is copied into the payload buffer, and the length of the reading is recorded in len.

If a sensor supports configuration (for example, temperature units in Fahrenheit or Celsius), a configuration read and configuration write function must be implemented, and provided to the sapi_register_sensor function for sensor registration.  The prototypes for sensor read and write configuration functions are:

/*
 * @brief Read sensor configuration. Builds and returns the payload. Callback called on
 *   CoAP Get configuration value
 *
 * @param payload     Pointer to the sensor payload buffer.
 * @param len         Pointer to the CoAP message buffer length.
 * @return SAPI Error Code
 */
sapi_error_t sensor_read_cfg(char *payload, uint8_t *len);

/*
 * @brief Write sensor configuration. Processes payload sent from client. Callback called on
 *   CoAP Put configuration value
 *
 * @param payload     Pointer to the sensor payload buffer.
 * @param len         Pointer to the CoAP message buffer length.
 * @return SAPI Error Code
 */
sapi_error_t sensor_write_cfg(char *payload, uint8_t *len);