Developing an Application for an Onboard Sensor
-----------------------------------------------

This tutorial shows you how to develop a simple application for an
onboard sensor. The Mynewt sensor framework enables you to easily and
quickly develop Mynewt sensor applications. We assume that you have
completed the :doc:`Enabling an Off-Board Sensor in an Existing Application
Tutorial <sensor_nrf52_bno055>` and are familiar with the sensor 
framework and sensor shell command.

This tutorial shows you how to:

-  Develop an application for the Nordic Thingy LIS2DH12 accelerometer
   onboard sensor with the sensor framework ``sensor`` shell command
   enabled to view sensor data.
-  Extend the application to use the sensor framework API to read the
   sensor data and output the data to the Mynewt console.

.. contents::
  :local:
  :depth: 2
  
Prerequisites
~~~~~~~~~~~~~

-  Meet the prerequisites listed in the :doc:`Sensor Tutorials
   Overview <sensors_framework>`
-  Have a Nordic Thingy.
-  `Segger J-Link Debug
   Probe <https://www.segger.com/jlink-debug-probes.html>`__.
-  `J-Link 9 pin Cortex-M
   Adapter <https://www.segger.com/jlink-adapters.html#CM_9pin>`__ that
   allows JTAG, SWD and SWO connections between J-Link and Cortex M
   based target hardware systems.
-  Install the `Segger JLINK Software and documentation
   pack <https://www.segger.com/jlink-software.html>`__.
-  Complete the :doc:`Enabling an Off-Board Sensor in an Existing Application
   Tutorial <sensor_nrf52_bno055>`

Developing a Sensor Enabled Application with Shell Support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We first develop a simple application with the LIS2DH12 onboard sensor
on the Nordic Thingy and the ``sensor`` shell command enabled.

Step 1: Creating a New App Package
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


We name the new app package ``my_sensor_app``. From your project base
directory, run the ``newt pkg new`` command to create a new app package.
This tutorial uses ~/dev/myproj for the project.

.. code-block:: console

    $ cd ~/dev/myproj
    $ newt pkg new -t app apps/my_sensor_app
    Download package template for package type app.
    Package successfuly installed into ~/dev/myproj/apps/my_sensor_app

The newt tool creates a skeleton ``my_sensor_app`` package directory in
the ``~/dev/myproj/apps/`` directory. Go to the ``my_sensor_app``
directory to update the package ``pkg.yml`` and source files.

.. code-block:: console


    $ cd apps/my_sensor_app

Step 2: Adding the Package Dependencies
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


The my\_sensor\_app package requires the sensor framework,
``hw/sensor``, package as a package dependency. Note that the BSP
creates the sensor devices for the onboard sensors, so the
``hw/sensor/creator`` package that creates off-board sensor is not
needed.

Add the highlighted line to the ``pkg.yml`` file to add the
``hw/sensor`` package as package dependency:

.. code-block:: console
   :emphasize-lines: 6   

    pkg.deps:
        - "@apache-mynewt-core/kernel/os"
        - "@apache-mynewt-core/sys/console/full"
        - "@apache-mynewt-core/sys/log/full"
        - "@apache-mynewt-core/sys/stats/full"
        - "@apache-mynewt-core/hw/sensor"


Step 3: Using the Skeleton main.c File
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


The newt tool creates a skeleton main.c file in the
``my_sensor_app/src`` directory. The skeleton ``main()`` code shown is
all you need to build an application that only uses the ``sensor`` shell
command to read sensor data. You do not need to make any changes to the
file. The sensor framework implements the ``sensor`` shell command and
the shell package processes shell command events from the OS default
event queue.

.. code-block:: c


    int
    main(int argc, char **argv)
    {
        /* Perform some extra setup if we're running in the simulator. */
    #ifdef ARCH_sim
        mcu_sim_parse_args(argc, argv);
    #endif

        /* Initialize all packages. */
        sysinit();

        /* As the last thing, process events from default event queue. */
        while (1) {
            os_eventq_run(os_eventq_dflt_get());
        }

        return 0;
    }

Step 4: Creating the Target for the my\_sensor\_app Application
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


You create a target for the my\_sensor\_app to run on the Nordic Thingy.
The following syscfg settings must be set:

-  ``I2C_0=1`` : Enables the I2C interface 0 for the nRF52 Thingy BSP
   HAL setting to communicate with the onboard sensor.
-  ``LIS2DH12_ONB=1``: Enables the lis2dh12 onboard sensor support in
   the nRF52 Thingy BSP.

   A BSP with onboard sensors defines a syscfg setting for each onboard
   sensor it supports and uses the naming convention
   ``<SENSORNAME>_ONB``. The ``<SENSORNAME>_ONB`` setting specifies
   whether the sensor named SENSORNAME is enabled. The setting is
   disabled by default. The BSP includes the sensor device driver
   package ``hw/drivers/sensors/<sensorname>`` and creates and
   configures the onboard sensor named SENSORNAME when the
   ``<SENSORNAME>_ONB`` setting is enabled by the application.

-  ``SHELL_TASK=1``: Enables the shell task for the shell command
   support. Note that the ``hw/sensor`` package enables the
   ``SENSOR_CLI`` setting by default.
-  ``SENSOR_OIC=0``: Disables the OIC sensor server support in the
   sensor framework.
-  ``CONSOLE_RTT=1``: Enables console communication via the SEGGER RTT.
   The nRF52 Thingy does not have a UART so we use the RTT for the
   console.
-  ``CONSOLE_UART=0``: Disables the console communication via a UART.

**Note:** The lis2dh12 sensor device driver package,
``/hw/driver/sensors/lis2dh12``, currently does not support a shell
command to view information on the device.

1. Run the following newt commands to create the target and set the
application and BSP.

.. code-block:: console


    $ newt target create thingy_my_sensor
    Target targets/thingy_my_sensor successfully created
    $ newt target set thingy_my_sensor bsp=@apache-mynewt-core/hw/bsp/nrf52-thingy
    Target targets/thingy_my_sensor successfully set target.bsp to @apache-mynewt-core/hw/bsp/nrf52-thingy
    $ newt target set thingy_my_sensor app=apps/my_sensor_app
    Target targets/thingy_my_sensor successfully set target.app to apps/my_sensor_app
    $ newt target set thingy_my_sensor build_profile=debug
    Target targets/thingy_my_sensor successfully set target.build_profile to debug

2. Run the following ``newt target set`` command to set the syscfg
settings:

.. code-block:: console


    $ newt target set thingy_my_sensor syscfg=I2C_0=1:LIS2DH12_ONB=1:SHELL_TASK=1:CONSOLE_RTT=1:CONSOLE_UART=0:SENSOR_OIC=0
    Target targets/thingy_my_sensor successfully set target.syscfg to I2C_0=1:LIS2DH12_ONB=1:SHELL_TASK=1:CONSOLE_RTT=1:CONSOLE_UART=0:SENSOR_OIC=0

Step 5: Creating and Building the Bootloader Target
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


Create a target for the bootloader for the nRF52 Thingy. We name the
target ``thingy_boot``.

1. Run the following ``newt target`` commands to create the target:

.. code-block:: console


    $ newt target create thingy_boot
    Target targets/thingy_boot successfully created
    $ newt target set thingy_boot bsp=@apache-mynewt-core/hw/bsp/nrf52-thingy
    Target targets/thingy_boot successfully set target.bsp to @apache-mynewt-core/hw/bsp/nrf52-thingy
    $ newt target set thingy_boot app=@mcuboot/boot/mynewt
    Target targets/thingy_boot successfully set target.app to @mcuboot/boot/mynewt
    $ newt target set thingy_boot build_profile=optimized
    Target targets/thingy_boot successfully set target.build_profile to optimized

2. Run the ``newt build`` command to build the bootloader target:

.. code-block:: console


    $ newt build thingy_boot
    Building target targets/thingy_boot

           ...

    Archiving thingy_boot-sysinit-app.a
    Archiving util_mem.a
    Linking ~/dev/myproj/bin/targets/thingy_boot/app/boot/mynewt/mynewt.elf
    Target successfully built: targets/thingy_boot

Step 6: Connecting the Thingy to your Computer
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Perform the following steps to connect the Thingy to your computer:

1. Move the power switch to the left to power ON the Thingy:

 |Thingy|

2. Connect the debug probe to the JTAG port on the board using the
Jlink 9-pin adapter and cable, and connect the probe to your computer.

 |J-Link debug probe to Thingy|

.. raw:: html

   <p>

Step 7: Loading the Image and Connecting to the Console via RTT
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


To run the application, you need to load the bootloader on to the
device, load the application image, and start a GDB debug process for
RTT to attach to.


1. Run the ``newt load`` command to load the bootloader:

.. code-block:: console

    $ newt load thingy_boot
    Loading bootloader


2. Run the ``newt run`` command to build and create an image for the
my\_sensor\_app, load the image, and start a GDB process to debug the
application:

.. code-block:: console

    $ newt run thingy_my_sensor 1.0.0
    Assembling repos/apache-mynewt-core/hw/bsp/nrf52-thingy/src/arch/cortex_m4/gcc_startup_nrf52_split.s
    Compiling repos/apache-mynewt-core/hw/cmsis-core/src/cmsis_nvic.c
    Assembling repos/apache-mynewt-core/hw/bsp/nrf52-thingy/src/arch/cortex_m4/gcc_startup_nrf52.s
    Compiling repos/apache-mynewt-core/encoding/base64/src/hex.c
    Compiling apps/my_sensor_app/src/main.c

        ...

    Archiving thingy_my_sensor-sysinit-app.a
    Archiving time_datetime.a
    Archiving util_cbmem.a
    Archiving util_crc.a
    Archiving util_mem.a
    Archiving util_parse.a
    Linking ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    App image succesfully generated: ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.img
    Loading app image into slot 1
    [~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy/nrf52-thingy_debug.sh ~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app]
    Debugging ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    GNU gdb (GNU Tools for ARM Embedded Processors) 7.8.0.20150604-cvs
    Copyright (C) 2014 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
    and "show warranty" for details.
    This GDB was configured as "--host=x86_64-apple-darwin10 --target=arm-none-eabi".
    Type "show configuration" for configuration details.
    For bug reporting instructions, please see:
    <http://www.gnu.org/software/gdb/bugs/>.
    Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.
    For help, type "help".
    Type "apropos word" to search for commands related to "word"...
    Reading symbols from ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf...done.
    os_tick_idle (ticks=24)
        at repos/apache-mynewt-core/hw/mcu/nordic/nrf52xxx/src/hal_os_tick.c:204
    204     if (ticks > 0) {
    Resetting target
    0x000000dc in ?? ()
    (gdb)

3. Enter ``c <return>`` in the (gdb) prompt to continue.

4. Run the following telnet command to connect to the Mynewt console
via RTT and enter <return> to get the shell prompt after you are
connected.

.. code-block:: console

    $ telnet localhost 19021
    Trying ::1...
    telnet: connect to address ::1: Connection refused
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    SEGGER J-Link V6.14h - Real time terminal output
    SEGGER J-Link ARM V10.0, SN=600000268
    Process: JLinkGDBServer

    011468 compat>

Step 8: Viewing the list of Sensors and Sensor Data
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1. Enter ``sensor list`` to see the sensors that are registered with
the sensor manager. You should see the ``lis2dh12_0`` sensor. This
sensor is only configured for the accelerometer (0x1).

.. code-block:: console


    011468 compat> sensor list
    sensor list
    029706 sensor dev = lis2dh12_0, configured type = 0x1
    029707 compat>

2. Enter the ``sensor read`` command to read some data samples from the
accelerometer:

.. code-block:: console


    029707 compat> sensor read lis2dh12_0 0x1 -n 5
    sensor read lis2dh12_0 0x1 -n 5
    042537 ts: [ secs: 331 usecs: 102682 cputime: 331436945 ]
    042537 x = 9.806650176 y = 58.839900992 z = -9894.910156
    042537 ts: [ secs: 331 usecs: 104832 cputime: 331439095 ]
    042537 x = 19.613300352 y = 98.066497804 z = -9924.330078
    042537 ts: [ secs: 331 usecs: 106988 cputime: 331441251 ]
    042537 x = 9.806650176 y = 49.033248902 z = -9904.716796
    042538 ts: [ secs: 331 usecs: 109137 cputime: 331443400 ]
    042538 x = 9.806650176 y = 29.419950496 z = -9904.716796
    042538 ts: [ secs: 331 usecs: 111288 cputime: 331445551 ]
    042538 x = 58.839900992 y = 0.000000000 z = -9816.457031
    042538 compat>

Extending the Application to Use the Sensor API to Read Sensor Data
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


As this tutorial demonstrates so far, the Mynewt sensor framework
enables you to easily and quickly develop an application with a sensor
and view the sensor data from the ``sensor`` shell command. We now
extend the application to use the sensor API to read the sensor data.

There are two sensor functions that you can use to read data from a
sensor device:

-  ``sensor_register_listener()``: This function allows you to register
   a listener for a sensor device. You specify a bit mask of the types
   of sensor data to listen for and a callback to call when data is read
   from the sensor device. The listener callback is called whenever the
   ``sensor_read()`` function reads data for a sensor type from a sensor
   device that the listener is listening for.

   The sensor framework supports polling of sensor devices. For a sensor
   device that has a polling rate configured, the sensor framework
   poller reads sensor data for all the configured sensor types from the
   sensor device at each polling interval and calls the registered
   listener callbacks with the sensor data.

-  ``sensor_read()``: This function reads sensor data from a sensor
   device and calls the specified user callback to receive the sensor
   data. You specify a bit mask of the types of sensor data to read from
   a sensor device and a callback. This callback is called for each
   sensor type you specify to read.

We first extend the application to a register a sensor listener to
demonstrate how to use the sensor framework polling support. We then
extend the application to use the ``sensor_read()`` function instead of
a listener. An application may not need to poll sensors. For example, an
application that processes remote requests for sensor data might only
read the sensor data when it receives a request.

Step 1: Modifying main.c to Add a Sensor Listener
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


Add the following code to the ``my_sensor_app/src/main.c`` file:

1. Add the highlighted include files:

.. code-block:: c
   :emphasize-lines: 4, 5, 6, 7

    #include "sysinit/sysinit.h"
    #include "os/os.h"
    
    #include <defs/error.h>
    #include <sensor/sensor.h>
    #include <sensor/accel.h>
    #include <console/console.h>
   
2. Add the ``struct sensor *my_sensor``. This is the handle for the
sensor that the sensor API uses to perform operations on the sensor. We
set this variable when we lookup the sensor.

.. code-block:: c

    static struct sensor *my_sensor;

3. Declare and initialize a sensor listener. You specify a bit mask for
the sensor types to listen for, the callback function, and an opaque
argument to pass to the callback. You initialize the type to
SENSOR\_TYPE\_ACCELEROMETER, the listener callback to the
``read_accelerometer()`` function, and the callback opaque argument to
the LISTENER\_CB value.

**Note**: We define LISTENER\_CB and READ\_CB values because we also use
the ``read_accelerometer()`` function as the callback for the
``sensor_read()`` function later in the tutorial. The LISTENER\_CB or
the READ\_CB value is passed to the ``read_accelerometer()`` function to
indicate whether it is invoked as a listener or a ``sensor_read()``
callback.

.. code-block:: c

    #define LISTENER_CB 1
    #define READ_CB 2

    static int read_accelerometer(struct sensor* sensor, void *arg, void *databuf, sensor_type_t type);

    static struct sensor_listener listener = {
       .sl_sensor_type = SENSOR_TYPE_ACCELEROMETER,
       .sl_func = read_accelerometer,
       .sl_arg = (void *)LISTENER_CB,
    };

4. Add the code for the ``read_accelerometer()`` function. The sensor
data is stored in the ``databuf`` and ``type`` specifies the type of
sensor data.

.. code-block:: c

    static int
    read_accelerometer(struct sensor* sensor, void *arg, void *databuf, sensor_type_t type)
    {

        char tmpstr[13];
        struct sensor_accel_data *sad;

        if (!databuf) {
            return SYS_EINVAL;

        }
        sad = (struct sensor_accel_data *)databuf;

        if (!sad->sad_x_is_valid ||
            !sad->sad_y_is_valid ||
            !sad->sad_z_is_valid) {

            return SYS_EINVAL;
        }

        console_printf("%s: [ secs: %ld usecs: %d cputime: %u ]\n",
                       ((int)arg == LISTENER_CB) ? "LISTENER_CB" : "READ_CB",
                       (long int)sensor->s_sts.st_ostv.tv_sec,
                       (int)sensor->s_sts.st_ostv.tv_usec,
                       (unsigned int)sensor->s_sts.st_cputime);

        console_printf("x = %s ", sensor_ftostr(sad->sad_x, tmpstr, 13));
        console_printf("y = %s ", sensor_ftostr(sad->sad_y, tmpstr, 13));
        console_printf("z = %s\n\n", sensor_ftostr(sad->sad_z, tmpstr, 13));
        return 0;
    }

5. Set the poll rate for the sensor to two seconds. The
``sensor_set_poll_rate_ms()`` function sets the poll rate for a named
sensor.

**Note:** You set the poll rate for a sensor programmatically and must
set the poll rate to a non zero value in order for the sensor manager to
poll the sensor. You may set a different poll rate for each sensor. The
sensor framework also defines a ``SENSOR_MGR_WAKEUP_RATE`` syscfg
setting that specifies the default rate that the sensor manager polls.
The sensor manager uses the poll rate for a sesnor if a sensor is
configured to poll more frequently than the ``SENSOR_MGR_WAKEUP_RATE``
setting value.

.. code-block:: c
   :emphasize-lines: 1, 2, 8, 15, 16

    #define MY_SENSOR_DEVICE "lis2dh12_0"
    #define MY_SENSOR_POLL_TIME 2000


    int 
    main(int argc, char **argv) 
    { 
        int rc;
        
        ...

        /* Initialize all packages. */
        sysinit();

        rc = sensor_set_poll_rate_ms(MY_SENSOR_DEVICE, MY_SENSOR_POLL_TIME);
        assert(rc == 0);


        /* As the last thing, process events from default event queue. */
        while (1) {
            os_eventq_run(os_eventq_dflt_get());
        }

        return 0;

    }

6. Look up the sensor by name to get the handle for the sensor and
register a listener for the sensor.

.. code-block:: c 
   :emphasize-lines: 10, 11, 12, 13

    int 
    main(int argc, char **argv) 
    { 
    
        ...

        rc = sensor_set_poll_rate_ms(MY_SENSOR_DEVICE, MY_SENSOR_POLL_TIME);
        assert(rc == 0);

        my_sensor = sensor_mgr_find_next_bydevname(MY_SENSOR_DEVICE, NULL);
        assert(my_sensor != NULL);
        rc = sensor_register_listener(my_sensor, &listener);
        assert(rc == 0);

        /* As the last thing, process events from default event queue. */
        while (1) {
            os_eventq_run(os_eventq_dflt_get());
        }

        return 0;

    }


Step 2: Rebuilding the Application and Connecting to Console
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


1. Run the ``newt run`` command to rebuild the application, create a
new image, load the image, and start a GDB process:

.. code-block:: console


    $ newt run thingy_my_sensor 2.0.0
    Compiling apps/my_sensor_app/src/main.c
    Archiving apps_my_sensor_app.a
    Linking ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    App image succesfully generated: ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.img
    Loading app image into slot 1
    [~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy/nrf52-thingy_debug.sh ~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app]
    Debugging ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    GNU gdb (GNU Tools for ARM Embedded Processors) 7.8.0.20150604-cvs

        ...

    Reading symbols from ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf...done.
    os_tick_idle (ticks=12)
        at repos/apache-mynewt-core/hw/mcu/nordic/nrf52xxx/src/hal_os_tick.c:204
    204     if (ticks > 0) {
    Resetting target
    0x000000dc in ?? ()
    (gdb) c
    Continuing.

2. Connect to the console via RTT:

.. code-block:: console

   $ telnet localhost 19021

    Connected to localhost.
    Escape character is '^]'.
    SEGGER J-Link V6.14h - Real time terminal output
    J-Link OB-SAM3U128-V2-NordicSemi compiled Mar  2 2017 12:22:13 V1.0, SN=682562963
    Process: JLinkGDBServer
    000003 LISTENER_CB: [ secs: 0 usecs: 23407 cputime: 331783 ]
    000003 x = 117.67980192 y = -19.61330035 z = -9885.103515

    000259 LISTENER_CB: [ secs: 2 usecs: 21190 cputime: 2327645 ]
    000259 x = 117.67980192 y = -9.806650176 z = -9914.523437

    000515 LISTENER_CB: [ secs: 4 usecs: 17032 cputime: 4323487 ]
    000515 x = 78.453201280 y = 0.000000000 z = -9924.330078

    000771 LISTENER_CB: [ secs: 6 usecs: 13131 cputime: 6319586 ]
    000771 x = 117.67980192 y = -19.61330035 z = -9914.523437

    001027 LISTENER_CB: [ secs: 8 usecs: 8810 cputime: 8315265 ]
    001027 x = 127.48645020 y = 0.000000000 z = -9924.330078

    001283 LISTENER_CB: [ secs: 10 usecs: 4964 cputime: 10311419 ]
    001283 x = 58.839900992 y = -9.806650176 z = -9885.103515

You should see the accelerometer sensor data output from the listener
callback.

Step 3: Modifying main.c to Use sensor\_read() Instead of a Listener
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Lets extend the application to use the ``sensor_read()`` function
instead of a listener. We setup an OS callout to call the
``sensor_read()`` function for illustration purposes. A real application
will most likely read the sensor data when it gets a request or some
other event.

1. Add an OS callout and initialize an OS timer to fire every 5
seconds. The timer callback calls the ``sensor_read()`` function to read
the sensor data. The ``read_accelerometer()`` callback is called when
the sensor data is read. The READ\_CB value is passed to the
``read_accelerometer()`` function and indicates that the callback is
from the ``sensor_read()`` function and not from the listener.

.. code-block:: c

    /*
     * Event callback function for timer events. The callback reads the sensor data
     */

    #define READ_SENSOR_INTERVAL (5 * OS_TICKS_PER_SEC)

    static struct os_callout sensor_callout;

    static void
    timer_ev_cb(struct os_event *ev)
    {


        assert(ev != NULL);

        /*
         * Read the accelerometer sensor.  Pass the READ_CB value for the callback opaque
         * arg to indicate that it is the sensor_read() callback.
         */
        sensor_read(my_sensor, SENSOR_TYPE_ACCELEROMETER, read_accelerometer,
                     (void *)READ_CB, OS_TIMEOUT_NEVER);
        os_callout_reset(&sensor_callout, READ_SENSOR_INTERVAL);
        return;
    }


    static void
    init_timer(void)
    {
        /*
         * Initialize the callout for a timer event.
         */
        os_callout_init(&sensor_callout, os_eventq_dflt_get(),
                        timer_ev_cb, NULL);

        os_callout_reset(&sensor_callout, READ_SENSOR_INTERVAL);
        return;
    }

2. Remove the listener registration and call the ``init_timer()``
function in ``main()``. You can delete the
``sensor_register_listener()`` function call, but we call the
``sensor_unregister_listener()`` function to illustrate how to use this
function.

.. code-block:: c
   :emphasize-lines: 10, 11, 13

    int
    main(int argc, char **argv)
    {
        ...

        assert(my_sensor != NULL);
        rc = sensor_register_listener(my_sensor, &listener);
        assert(rc == 0);

        rc = sensor_unregister_listener(my_sensor, &listener);
        assert(rc == 0);
        
        init_timer();

        /* As the last thing, process events from default event queue. */
        while (1) {
            os_eventq_run(os_eventq_dflt_get());
        }

        return 0;
    }

Step 4: Rebuilding the Application and Connecting to Console
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1. Run the ``newt run`` command to rebuild the application, create an new
image, and start a GDB process:

.. code-block:: console

    $ newt run thingy_my_sensor 3.0.0
    Compiling apps/my_sensor_app/src/main.c
    Archiving apps_my_sensor_app.a
    Linking ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    App image succesfully generated: ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.img
    Loading app image into slot 1
    [~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy/nrf52-thingy_debug.sh ~/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52-thingy ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app]
    Debugging ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf
    GNU gdb (GNU Tools for ARM Embedded Processors) 7.8.0.20150604-cvs

         ...

    Reading symbols from ~/dev/myproj/bin/targets/thingy_my_sensor/app/apps/my_sensor_app/my_sensor_app.elf...done.
    os_tick_idle (ticks=12)
        at repos/apache-mynewt-core/hw/mcu/nordic/nrf52xxx/src/hal_os_tick.c:204
    204     if (ticks > 0) {
    Resetting target
    0x000000dc in ?? ()
    (gdb) c
    Continuing.

3. Connect to the console via RTT:

.. code-block:: console


    $ telnet localhost 19021
    Trying ::1...
    telnet: connect to address ::1: Connection refused
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    SEGGER J-Link V6.14h - Real time terminal output
    J-Link OB-SAM3U128-V2-NordicSemi compiled Mar  2 2017 12:22:13 V1.0, SN=682562963
    Process: JLinkGDBServer


    000629 compat> READ_CB: [ secs: 5 usecs: 4088 cputime: 5295643 ]
    000642 x = 98.066497804 y = 0.000000000 z = -9806.650390

    001282 READ_CB: [ secs: 9 usecs: 992459 cputime: 10284014 ]
    001282 x = 117.67980192 y = -39.22660064 z = -9894.910156

    001922 READ_CB: [ secs: 14 usecs: 981159 cputime: 15272714 ]
    001922 x = 78.453201280 y = -29.41995049 z = -9885.103515

    002562 READ_CB: [ secs: 19 usecs: 970088 cputime: 20261643 ]
    002562 x = 107.87315366 y = -29.41995049 z = -9885.103515

You should see the accelerometer sensor data output from the sensor read
data callback.

.. |Thingy| image:: ../pics/thingy.jpg
.. |J-Link debug probe to Thingy| image:: ../pics/thingy_jlink.jpg