diff --git a/Makefile b/Makefile
index 5985440..fb3f88c 100644
--- a/Makefile
+++ b/Makefile
@@ -25,38 +25,39 @@ endif
 BINARY = firmware
 
 # which development board is used
-# supported are: SYSTEM_BOARD, MAPLE_MINI, BLUE_PILL
-BOARD = BLUE_PILL
+# supported are: SYSTEM_BOARD, MAPLE_MINI, BLUE_PILL, CORE_BOARD
+BOARD = CORE_BOARD
 
 # source files
 CSRC = $(wildcard *.c)
 CHDR = $(wildcard *.h)
 OBJ = $(patsubst %.c,%.o,$(CSRC))
-# figure out based on the includes which library files are used in the main CSRC files
-DEPENDENCIES = $(patsubst %.c,%.inc,$(CSRC))
 
 # my library collection
 LIB = lib
-# the library files to use
-# this will be populated using includes based DEPENDENCIES
+# the library files to use (this will be populated using includes based DEPENDENCIES)
 LIB_CSRC =
 LIB_CHDR = $(patsubst %.c,%.h,$(LIB_CSRC))
 LIB_OBJ = $(patsubst %.c,%.o,$(LIB_CSRC))
+
+# figure out based on the includes which library files are used in the main CSRC files
+DEPENDENCIES = $(patsubst %.c,%.inc,$(CSRC))
 # populates LIB_CSRC based on the library files used
 -include $(DEPENDENCIES)
 
 # executables for linking, compiling, debugging, ...
-PREFIX ?= arm-none-eabi
-# use gcc as compiler
-CC := $(PREFIX)-gcc
-# use clang as compiler
-#CC := clang -target $(PREFIX)
+# use ELLCC cross-compiling chain (based on clang/llvm + musl)
+ELLCC := /opt/ellcc/
+# use ELLCC as compile
+CC := $(ELLCC)bin/ecc -target arm-none-eabi
 LD := $(PREFIX)-ld
-AR := $(PREFIX)-ar
-AS := $(PREFIX)-as
-OBJCOPY := $(PREFIX)-objcopy
-OBJDUMP := $(PREFIX)-objdump
-GDB := $(PREFIX)-gdb
+LD := $(ELLCC)bin/ecc-ld -m armelf
+AR := $(ELLCC)bin/ecc-ar
+AS := $(ELLCC)bin/ecc-as
+OBJCOPY := $(ELLCC)bin/ecc-objcopy
+OBJDUMP := $(ELLCC)bin/ecc-objdump
+# ecc-gdb is buggy and crashes on "kill"
+GDB := gdb
 
 # opencm3 libraries
 OPENCM3_DIR := libopencm3
@@ -70,6 +71,8 @@ ifeq ($(BOARD),SYSTEM_BOARD)
 LDSCRIPT = $(OPENCM3_DIR)/lib/stm32/f1/stm32f103x8.ld
 else ifeq ($(BOARD),BLUE_PILL)
 LDSCRIPT = $(OPENCM3_DIR)/lib/stm32/f1/stm32f103x8.ld
+else ifeq ($(BOARD),CORE_BOARD)
+LDSCRIPT = $(OPENCM3_DIR)/lib/stm32/f1/stm32f103x8.ld
 else ifeq ($(BOARD),MAPLE_MINI)
 LDSCRIPT = $(OPENCM3_DIR)/lib/stm32/f1/stm32f103xb.ld
 endif
@@ -81,7 +84,7 @@ DEFS += -DSTM32F1 -D$(BOARD)
 # optimize for size
 CFLAGS += -Os
 # add debug symbols (remove for smaller release)
-CFLAGS += -g
+CFLAGS += -ggdb
 # use C99 (supported by most an sufficient)
 CFLAGS += -std=c99
 # have strict warning (for better code)
@@ -90,18 +93,14 @@ CFLAGS += -Wpedantic -Wall -Werror -Wundef -Wextra -Wshadow -Wredundant-decls -W
 CFLAGS += -fno-common -ffunction-sections -fdata-sections
 # use variable size enum (opencm3, gcc, and compiler-rt do)
 CFLAGS += -fshort-enums
-# use no variable size enum (musl does not)
-#CFLAGS += -fno-short-enums
+# use no variable size enum (ELLCC/musl does not)
+CFLAGS += -fno-short-enums
 # don't use system main definition (the starting point)
 CFLAGS += -ffreestanding
 # don't use the standard library
-#CFLAGS += -nostdlib -nostdinc
-# include musl libc
-#CFLAGS += -I /media/data/tmp/arm-linux-musleabi/arm-linux-musleabi/include
-# include newlib libc
-#CFLAGS += -I/usr/arm-none-eabi/include/
-# include gcc standard library (for printf)
-#CFLAGS += -I/usr/lib/gcc/arm-none-eabi/6.1.1/include/
+CFLAGS += -nostdlib -nostdinc
+# include ELLCC libraries
+CFLAGS += -I$(ELLCC)libecc/include/ -I$(ELLCC)libecc/include/arm/
 # include own libraries 
 CFLAGS += -I . $(patsubst %,-I%,$(LIB))
 # include opencm3 libraries
@@ -117,32 +116,22 @@ LDFLAGS += -nostartfiles
 # only keep used sections
 LDFLAGS += --gc-sections
 # don't use system libraries
-#LDFLAGS += -nostdlib -nostdinc
-# add musl libraries (for libc, libm)
-#LDFLAGS += --library-path /media/data/tmp/arm-linux-musleabi/arm-linux-musleabi/lib
-# add system libraries (for libc, libm, libnosys)
-LDFLAGS += --library-path /usr/arm-none-eabi/lib/armv7-m/
-# add gcc library (for ARM ABI to be used by gcc)
-LDFLAGS += --library-path /usr/lib/gcc/arm-none-eabi/*/armv7-m/
-# add compiler-rt library (for ARM ABI to be used by clang)
-#LDFLAGS += --library-path /usr/arm-none-eabi/lib/armv7-m/
+LDFLAGS += -nostdlib -nostdinc
+# add ELLCC standard libraries (for libc, libm, libgcc)
+LDFLAGS += --library-path $(ELLCC)libecc/lib/cortex-m3-linux/
 # opencm3 libraries
 LDFLAGS += --library-path $(OPENCM3_LIB)
-
 # linker script with definitions for micro-controller
 LDFLAGS += --script $(LDSCRIPT)
-
-# used libraries when using gcc (must be provided after objects)
-LDLIBS += --library $(STM32F1_LIB) --library c --library gcc --library nosys --library m
-# used libraries when using clang (must be provided after objects)
-#LDLIBS += --library $(STM32F1_LIB) --library c --library m --library clang_rt.builtins
+# used libraries (gcc provides the ARM ABI, not sure how to replace with compiler-rt)
+LDLIBS += --library $(STM32F1_LIB) --library c --library m --library gcc
 
 # target micro-controller information (ARM Cortex-M3 supports thumb and thumnb2, but does not include a floating point unit)
 ARCH_FLAGS = -mthumb -mcpu=cortex-m3 -msoft-float
 
 # SWD adapter used
 # supported are : st-link v2 (STLINKV2), black magic probe (BMP)
-SWD_ADAPTER ?= STLINKV2
+SWD_ADAPTER ?= BMP
 ifeq ($(SWD_ADAPTER),STLINKV2)
 # OpenOCD configuration
 OOCD ?= openocd
@@ -192,14 +181,14 @@ list: $(BINARY).list
 
 # figure out which library source files are used for later inclusion
 %.inc: %.d
-	$(Q)grep -o -e " ${LIB}\/[^ ]*\.h" $(<) | sed -e 's/\.h$$/.c/g' -e 's/^/LIB_CSRC +=/' > $(@)
+	$(Q)grep -o -e " ${LIB}\/[^ ]*\.h" $(<) | sed -e 's|\(.*\)\.h$$|LIB_CSRC +=\1.c\n-include\1.inc|g' -e 's|.*${*}.*||g' > $(@)
 
 # doxygen documentation
 doc: Doxyfile README.md $(CSRC) $(CHDR) $(LIB_CSRC) $(LIB_CHDR)
 	$(Q)doxygen $(<)
 
 clean:
-	$(Q)$(RM) $(BINARY).elf $(BINARY).bin $(BINARY).hex $(BINARY).map $(OBJ) $(LIB_OBJ) $(LIB)/*.o $(DEPENDENCIES)
+	$(Q)$(RM) $(BINARY).elf $(BINARY).bin $(BINARY).hex $(BINARY).map $(OBJ) $(LIB_OBJ) $(LIB)/*.o $(DEPENDENCIES) $(LIB)/*.inc
 
 # make libopencm3 if library for STM32F1 is not yet existing
 $(OPENCM3_LIB)/lib$(STM32F1_LIB).a:
@@ -213,7 +202,7 @@ flash: $(BINARY).hex
 ifeq ($(SWD_ADAPTER),STLINKV2)
 	$(Q)$(OOCD) --file interface/$(OOCD_INTERFACE).cfg --file target/$(OOCD_TARGET).cfg --command "init" --command "reset init" --command "flash write_image erase $(<)" --command "reset" --command "shutdown" $(NULL)
 else ifeq ($(SWD_ADAPTER),BMP)
-	$(Q)$(GDB) --eval-command="target extended-remote $(BMPPORT)" --eval-command="monitor version" --eval-command="monitor swdp_scan" --eval-command="attach 1" --eval-command="load" --eval-command="detach" --eval-command="kill" --eval-command="quit" $(<)
+	$(Q)$(GDB) --eval-command="target extended-remote $(BMPPORT)" --eval-command="set confirm off" --eval-command="kill" --eval-command="monitor swdp_scan" --eval-command="attach 1" --eval-command="load" --eval-command="kill" --eval-command="detach" --eval-command="quit" $(<)
 endif
 
 # reset device by setting the data width to 5 bis on the USB CDC ACM port