"SparkFun SAMD21 Mini Breakout" 'Serial1' was not declared in this scope I recently switched computers and installed Arduino IDE, Added SAMD21 to the boards manager and installed drivers.
My sketch previously ran on my laptop with no problems.  Now when I try to compile for the SAMD21 Mini, I get a 'Serial1' was not declared in this scope error.
If I try to compile it for Mega, there are no problems.
I have tried sample code with Serial1 for SAMD21 and it compiled and uploaded with no problems.
Ahhhh, I figured it out.  I had to add #include &quot;Arduino.h&quot; to the .cpp file.