Building for TTN OTAA example on Feather M0 for debugging using PlatformIO and BlackMagic Probe

platformio.ini

; Instructions
; - Install PlatformIO IDE Package within Atom and then choose PlatformIO / Install Shell Commands menu item
; - Alternatively install PlatformIO command line only (when you install for Atom it will want you to then remove the cli version)
; - Upgrade to development version of atmelsam platform using the following commands
;   pio platform uninstall atmelsam
;   pio platform install https://github.com/platformio/platform-atmelsam.git
; - Make a directory myproject
; - Copy this fileinto it as platformio.ini
; - Copy ttn-otaa.ino to myproject/src/main.cpp
; - Make sure that arm-none-eabi-gdb is on your path. Might have to run:
;   export PATH=~/.platformio/packages/toolchain-gccarmnoneeabi/bin:$PATH
; - Build and Run
;   pio debug --interface gdb
; - At the (gdb) prompt load the executable with
;   source .pioinit
; - You should see something like
;     Target voltage: 3.3V
;     Available Targets:
;     No. Att Driver
;      1      Atmel SAMD21G18A (rev D)
;     0x000021c8 in ?? ()
;     Loading section .text, size 0x8894 lma 0x0
;     Loading section .ramfunc, size 0x60 lma 0x8894
;     Loading section .ARM.exidx, size 0x8 lma 0x88f4
;     Loading section .data, size 0x120 lma 0x88fc
;     Start address 0x1b84, load size 35356
;     Transfer rate: 16 KB/sec, 906 bytes/write.
;     Breakpoint 2 at 0x462: file src/main.cpp, line 167.
; [Ctrl-C breaks you out of GDB, which is unworkable. But at this point you can run under Atom (PlatformIO/Debug menu) 
;  where Ctrl-C works right and you get all the visual debugging sweets.]
; Using a OpenOCD and a different JTAG connector, you'll have to edit debug_tool/port accordingly
; See http://docs.platformio.org/en/latest/plus/debugging.html#openocd-and-st-link

[common]
lib_deps_builtin = SPI
lib_deps_external = https://github.com/things-nyc/arduino-lmic.git

[env:feather]
platform = atmelsam
board = adafruit_feather_m0
framework = arduino
build_flags =
  -ggdb3
  -Wl,-T"flash_without_bootloader.ld"
debug_tool = blackmagic
debug_port = /dev/cu.usbmodem7BB07991
debug_extra_cmds =
  break setup
lib_deps =
  ${common.lib_deps_builtin}
  ${common.lib_deps_external}