Enabling The Console and Shell for Blinky

This tutorial shows you how to add the Console and Shell to the Blinky application and interact with it over a serial line connection.


Use an Existing Project

Since all we’re doing is adding the shell and console capability to blinky, we assume that you have worked through at least some of the other tutorials, and have an existing project. For this example, we’ll be modifying the blinky on nRF52 project to enable the shell and console connectivity. You can use blinky on a different board.

Modify the Dependencies and Configuration

Modify the package dependencies in your application target’s pkg.yml file as follows:

  • Add the shell package: @apache-mynewt-core/sys/shell.

  • Replace the @apache-mynewt-core/sys/console/stub package with the @apache-mynewt-core/sys/console/full package.

    Note: If you are using version 1.1 or lower of blinky, the @apache-mynewt-core/sys/console/full package may be already listed as a dependency.

The updated pkg.yml file should have the following two lines:

    - "@apache-mynewt-core/sys/console/full"
    - "@apache-mynewt-core/sys/shell"

This lets the newt system know that it needs to pull in the code for the console and the shell.

Modify the system configuration settings to enable Shell and Console ticks and prompt. Add the following to your application target’s syscfg.yml file:

    # Enable the shell task.

Use the OS Default Event Queue to Process Blinky Timer and Shell Events

Mynewt creates a main task that executes the application main() function. It also creates an OS default event queue that packages can use to queue their events. Shell uses the OS default event queue for Shell events, and main() can process the events in the context of the main task.

Blinky’s main.c is very simple. It only has a main() function that executes an infinite loop to toggle the LED and sleep for one second. We will modify blinky:

  • To use os_callout to generate a timer event every one second instead of sleeping. The timer events are added to the OS default event queue.

  • To process events from the OS default event queue inside the infinite loop in main().

This allows the main task to process both Shell events and the timer events to toggle the LED from the OS default event queue.

Modify main.c

Initialize a os_callout timer and move the toggle code from the while loop in main() to the event callback function. Add the following code above the main() function:

/* The timer callout */
static struct os_callout blinky_callout;

 * Event callback function for timer events. It toggles the led pin.
static void
timer_ev_cb(struct os_event *ev)
    assert(ev != NULL);


    os_callout_reset(&blinky_callout, OS_TICKS_PER_SEC);

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

    os_callout_reset(&blinky_callout, OS_TICKS_PER_SEC);

In main(), add the call to the init_timer() function before the while loop and modify the while loop to process events from the OS default event queue:

main(int argc, char **argv)

    int rc;

#ifdef ARCH_sim
    mcu_sim_parse_args(argc, argv);


    g_led_pin = LED_BLINK_PIN;
    hal_gpio_init_out(g_led_pin, 1);
    while (1) {
    return rc;

Build, Run, and Upload the Blinky Application Target

We’re not going to build the bootloader here since we are assuming that you have already built and loaded it during previous tutorials.

We will use the newt run command to build and deploy our improved blinky image. The run command performs the following tasks for us:

  1. Builds a binary Mynewt executable

  2. Wraps the executable in an image header and footer, turning it into a Mynewt image.

  3. Uploads the image to the target hardware.

  4. Starts a gdb process to remotely debug the Mynewt device.

Run the newt run nrf52_blinky 0 command. The 0 is the version number that should be written to the image header. Any version will do, so we choose 0.

$ newt run nrf52_blinky 0


Archiving util_mem.a
Linking /home/me/dev/myproj/bin/targets/nrf52_blinky/app/apps/blinky/blinky.elf
App image succesfully generated: /home/me/dev/myproj/bin/targets/nrf52_blinky/app/apps/blinky/blinky.elf
Loading app image into slot 1
[/home/me/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52dk/nrf52dk_debug.sh /home/me/dev/myproj/repos/apache-mynewt-core/hw/bsp/nrf52dk /home/me/dev/myproj/bin/targets/nrf52_blinky/app/apps/blinky]
Debugging /home/me/dev/myproj/bin/targets/nrf52_blinky/app/apps/blinky/blinky.elf

Set Up a Serial Connection

You’ll need a Serial connection to see the output of your program. You can reference the Using the Serial Port with Mynewt OS Tutorial for more information on setting up your serial communication.

Communicate with the Application

Once you have a connection set up, you can connect to your device as follows:

  • On Mac OS and Linux platforms, you can run minicom -D /dev/tty.usbserial-<port> -b 115200 to connect to the console of your app. Note that on Linux, the format of the port name is /dev/ttyUSB<N>, where N is a number.

  • On Windows, you can use a terminal application such as PuTTY to connect to the device.

If you located your port from a MinGW terminal, the port name format is /dev/ttyS<N>, where N is a number. You must map the port name to a Windows COM port: /dev/ttyS<N> maps to COM<N+1>. For example, /dev/ttyS2 maps to COM3.

You can also use the Windows Device Manager to locate the COM port.

To test and make sure that the Shell is running, first just hit :

004543 shell>

You can try some commands:

003005 shell> help
003137 Available modules:
003137 os
003138 prompt
003138 To select a module, enter 'select <module name>'.
003140 shell> prompt
003827 help
003827 ticks                         shell ticks command
004811 shell> prompt ticks off
005770  Console Ticks off
shell> prompt ticks on
006404  Console Ticks on
006404 shell>