Flashing a device with Samples

Now we're getting to the good stuff - working with hardware! The sample project provided will demonstrate a device securely communicating with Golioth and will also introduce the first device service for logging.

The sample we'll be using is called hello, which logs a "hello" message using the Logging Device Service. Here's snippet of the main() function:

void main(void)
int r;
int counter = 0;
LOG_DBG("Start Hello sample");
k_sem_take(&golioth_client_ready, K_FOREVER);
while (true) {
LOG_INF("Sending hello! %d", counter++);
r = golioth_send_hello(client);
if (r < 0) {
LOG_WRN("Failed to send hello!");

If you're familiar with Zephyr you may recognized the LOG_* functions. That's because Golioth tries to use Zephyr APIs whenever it can. In this instance, the Logging Device Service is a cloud-enabled backend for Zephyr's logging library. In this way, Golioth can reuse well-tested libraries, reduce the size through shared code and feel idiomatic to developers who are comfortable with Zephyr.

Building hello#

Samples can be found in the Zephyr SDK in the folder modules/lib/golioth/samples. We recommend running the commands below from the modules/lib/golioth folder.

cd ~/zephyrproject/modules/lib/golioth

Zephyr uses Kconfig to manage build settings at scale. Kconfig values can be set a number of ways but for this example we'll take a simple route by modifying prj.conf.

Open samples/hello/prj.conf in your editor of choice and add these fields:


Set the PSK & PSK ID to match what was used during the provisioning step and the Wi-Fi network credentials to match your network.

After saving, build the sample with the new settings applied.

west build -b esp32 samples/hello

Flashing the device#

Flashing is a simple west command away.

west flash --esp-device=/dev/cu.usbserial-1337

Your ESP32 will likely be at a different location, so adjust the flash command accordingly.

Verify with serial output#

You can verify that everything is working by connecting to the device over a serial console using a tool like screen:

screen /dev/cu.usbserial-1337 115200

This is an snippet from the serial console:

[00:00:00.000,000] <dbg> golioth_hello.main: Start CoAP-client sample
[00:00:00.000,000] <inf> golioth_hello: Initializing golioth client
[00:00:00.000,000] <inf> golioth_hello: Golioth client initialized
[00:00:00.000,000] <inf> golioth_hello: Sending hello! 0
[00:00:00.000,000] <dbg> golioth_hello.main: Debug info! 1
[00:00:00.000,000] <dbg> golioth_hello.func_1: Log 1: 1
[00:00:00.000,000] <dbg> golioth_hello.func_2: Log 2: 1
[00:00:00.000,000] <wrn> golioth_hello: Warn: 1
[00:00:00.000,000] <err> golioth_hello: Err: 1
[00:00:00.000,000] <inf> golioth_hello: Starting connect
[00:00:00.000,000] <inf> golioth_hello: Client connected!

These are just the logs the device has created but they're also being sent to Golioth for later use. The next step will show you how to view logs from the cloud.