Dear Marti and William

Thank you for your reply.

I tried using "--bossac-port", but still have problem about "-o" option.

I checked my bossac option by
```
$ ~/Zephyr_191116/zephyr-sdk-0.10.3/sysroots/x86_64-pokysdk-linux/usr/bin/bossac --help
```

```

There is no "-o" option for my bossac.
My environment is Ubuntu 18.04 LTS.

I have found this.
Adafruit Trinket M0 Bossac Offset is Wrong #16052
https://github.com/zephyrproject-rtos/zephyr/issues/16052

For Adafruit Trinket M0, the address is specified using "-o 0x2000". However, because my bossac does not have "-o" option, the problem occurs.
It seems that I have to update my environment to have newer? bossac version.