How to use RIOT-OS on Axio-Builder

Download the RIOT-OS source code from the sp-axio github page.
Go to the example directory you want to run on the Axio-Builder.
Compile with BOARD value as shown below.
```
$ BOARD=axio-builder-ms500 make
```
After signing the generated executable file, upload it to the Axio-Builder with the following command. (Specify the serial-port of the Axio-builder board as the PORT value.)
```
$ BOARD=axio-builder-ms500 make flash PORT=/dev/ttyUSB0
```
If the upload process is successful, you will see the following message. At this time, press the reset button of Axio-Builder.
```
### Flashing axio-builder-ms500 ###
example.bin.sig has been created.
Please reset the board.
```
After the procedure is completed, press the reset button again.
```
.....................
Download Success.
Please reset the board.
```
You can check the execution result at the terminal with the following command. (Specify the serial-port of the Axio-builder board as the PORT value.)
```
$ BOARD=axio-builder-ms500 make term PORT=/dev/ttyUSB0
```
You can execute steps 3 ~ 5 with one command. (Specify the serial-port of the Axio-builder board as the PORT value.)
```
$ BOARD=axio-builder-ms500 make flash term PORT=/dev/ttyUSB0
```