Blinky on mbed CLI

Quick start video

Tip: the video assumes you’ve already installed mbed CLI.

Video tutorialWatch how to create your first application on mbed CLI

Blinky’s code

#include "mbed.h"
#include "rtos.h"

DigitalOut led1(LED1);

// main() runs in its own thread in the OS
// (note the calls to wait below for delays)
int main() {
    while (true) {
        led1 = !led1;

Installing mbed CLI and a toolchain

mbed CLI is an offline tool, meaning you’ll have to install it before you can work. You will also need to install a toolchain. Please follow the installation instructions on the mbed CLI page, and come back here when you’re done.

Setting context

Whenever you work with mbed CLI, you need to navigate your command-line terminal to the directory in which you want to work. For example, if your program is in a folder called my_program:

cd my_program
mbed <commands>

Getting Blinky

mbed CLI can import Blinky, along with the mbed OS codebase. The import process creates a new directory as a subdirectory of your current context (as explained above).

To import Blinky, from the command-line:

  1. Navigate to a directory of your choice. We’re navigating to our development directory:

    cd dev_directory

  2. Import the example:

    mbed import mbed-os-example-blinky cd mbed-os-example-blinky
    Tip: import requires a full URL to Mercurial or GitHub. If you don’t enter a full URL, mbed CLI prefixes your snippet with We took advantage of this feature in our example; import mbed-os-example-blinky is interpreted as

Blinky is now under dev_directory > mbed-os-example-blinky. You can look at main.cpp to familiarize yourself with the code.


Invoke mbed compile, specifying:

  • Your board: -m <board_name>.
  • Your toolchain: -t <GCC_ARM`, `ARM` or `IAR`>.

For example, for the board K64F and the ARM Compiler 5:

mbed compile -m K64F -t ARM

Your PC may take a few minutes to compile your code. At the end you should get the following result:

| Module                     | .text | .data | .bss |
| Misc                       | 13939 |    24 | 1372 |
| core/hal                   | 16993 |    96 |  296 |
| core/rtos                  |  7384 |    92 | 4204 |
| features/FEATURE_IPV4      |    80 |     0 |  176 |
| frameworks/greentea-client |  1830 |    60 |   44 |
| frameworks/utest           |  2392 |   512 |  292 |
| Subtotals                  | 42618 |   784 | 6384 |
Allocated Heap: unknown
Allocated Stack: unknown
Total Static RAM memory (data + bss): 7168 bytes
Total RAM memory (data + bss + heap + stack): 7168 bytes
Total Flash memory (text + data + misc): 43402 bytes
Image: .\.build\K64F\ARM\mbed-os-example-blinky.bin             

The program file, mbed-os-example-blinky.bin, is under your build\K64F\ARM\ folder.

Programming your board

mbed Enabled boards are programmable by drag and drop over a USB connection.

  1. Connect your mbed board to the computer over USB.
  2. Copy the binary file to the board. In the example above, the file is mbed-os-example-blinky.bin, and it’s under the build\K64F\ARM\ folder.
  3. Press the reset button to start the program.

You should see the LED of your board turning on and off.