Improvements

platformio.ini

@@ -13,7 +13,7 @@
 [platformio]
 src_dir      = Marlin
 boards_dir   = buildroot/share/PlatformIO/boards
-default_envs = LPC1768
+default_envs = STM32F103RC_btt
 include_dir  = Marlin
 extra_configs =
     Marlin/config.ini
@@ -147,3 +147,15 @@ platform         = atmelavr
 board            = megaatmega2560
 build_flags      = -c -H -std=gnu++11 -Wall -Os -D__MARLIN_FIRMWARE__
 build_src_filter = +<src/MarlinCore.cpp>
+
+[env:STM32F103RC_btt]
+platform = ststm32
+board = genericSTM32F103RC
+framework = arduino
+build_flags =
+  -DUSART2_RX_PIN=PD6
+  -DUSART2_TX_PIN=PD5
+  -DDEBUG_UART=USART2
+  ${common.build_flags}
+extra_scripts = ${common.extra_scripts}
+lib_deps = ${common.lib_deps}