Developing / expanding an existing platform with a builder script if never done before can be daunting. I’ll have a look at your repos and finish the work and tell you what was missing.
Did you push your modified platform-atmelsam too?
I have now! 
So here is my modified atmelsam platform:
And here is the arduino framework:
Thank you! 
I have taken a look at it and you have not correctly translated the board.txt options for this board and the correspoding usage in the platform.txt into the extra_flags macros for the board. Further you misdeclared the core as a Cortex-M0 when it’s an Cortex-M0+, overstated RAM and FLASH size by multiple factors, missed hwid definitions and USB metainfo. I’ve fixed these in Fix board definition and builder logic · maxgerhardt/platformio-atmelsam@262d663 · GitHub. I further equalized the used GCC compiler and the Atmel CMSIS package in Fix package version for atmel cmsis and compiler · maxgerhardt/platformio-atmelsam@caa234e · GitHub.
Try using
[env:samd11c14a]
platform = https://github.com/maxgerhardt/platformio-atmelsam
board = samd11c14a
framework = arduino
upload_protocol = sam-ba
with
#include <Arduino.h>
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println("test test");
delay(1000);
}
Use the CLI → pio platform update atmelsam to make sure all git versions are the latest.
Thank you!!
I couldn’t make it work yet, I fried my only samd board with static electricity… but I’ll try next week again and let you know how it went.