diff --git a/F0-nolib/ch340/Makefile b/F0-nolib/ch340/Makefile
index b3f0ceb..a72fdf8 100644
--- a/F0-nolib/ch340/Makefile
+++ b/F0-nolib/ch340/Makefile
@@ -22,7 +22,6 @@ ARCH_FLAGS	= $(ASM_FLAGS) $(FP_FLAGS)
 ###############################################################################
 # Executables
 OPREFIX		?= /opt/bin/arm-none-eabi
-#PREFIX		?= /usr/x86_64-pc-linux-gnu/arm-none-eabi/gcc-bin/7.3.0/arm-none-eabi
 PREFIX		?= $(OPREFIX)
 
 RM			:= rm -f
diff --git a/F1-nolib/led_blink/Makefile b/F1-nolib/led_blink/Makefile
index 7620c9b..c1879da 100644
--- a/F1-nolib/led_blink/Makefile
+++ b/F1-nolib/led_blink/Makefile
@@ -5,28 +5,28 @@ BOOTSPEED	?= 115200
 FAMILY		?= F1
 # MCU code
 MCU			?= F103xB
-#density (stm32f10x.h, lines 70-84)
+# density (stm32f10x.h, lines 70-84)
 DENSITY 	?= MD
-DEFS		= -DEBUG
 # change this linking script depending on particular MCU model,
-# for example, if you have STM32F103VBT6, you should write:
 LDSCRIPT	?= ld/stm32f103xB.ld
-#LDSCRIPT = STM32F103C8.ld
+# debug
+DEFS		= -DEBUG
 
 INDEPENDENT_HEADERS=
 
 FP_FLAGS	?= -msoft-float
 ASM_FLAGS	?= -mthumb -mcpu=cortex-m3 
-#-mfix-cortex-m3-ldrd
 ARCH_FLAGS	= $(ASM_FLAGS) $(FP_FLAGS)
 
 ###############################################################################
 # Executables
-PREFIX		?= arm-none-eabi
-
+#PREFIX		?= arm-none-eabi
+# gcc from arm web site 
+PREFIX		?= /opt/bin/arm-none-eabi
 RM			:= rm -f
 RMDIR		:= rmdir
 CC			:= $(PREFIX)-gcc
+# don't replace ld with gcc: the binary size would be much greater!!
 LD			:= $(PREFIX)-ld
 AR			:= $(PREFIX)-ar
 AS			:= $(PREFIX)-as
@@ -36,15 +36,16 @@ OBJDUMP		:= $(PREFIX)-objdump
 GDB			:= $(PREFIX)-gdb
 STFLASH		:= $(shell which st-flash)
 STBOOT		:= $(shell which stm32flash)
+DFUUTIL		:= $(shell which dfu-util)
 
 ###############################################################################
 # Source files
 OBJDIR 		= mk
-LDSCRIPT	?= $(BINARY).ld
 SRC			:= $(wildcard *.c)
 OBJS		:= $(addprefix $(OBJDIR)/, $(SRC:%.c=%.o))
 STARTUP		= $(OBJDIR)/startup.o
 OBJS 		+= $(STARTUP)
+# dependencies: we need them to recompile files if their headers-dependencies changed
 DEPS		:= $(OBJS:.o=.d)
 
 INC_DIR ?= ../inc
@@ -54,35 +55,22 @@ LIB_DIR		:= $(INC_DIR)/ld
 
 ###############################################################################
 # C flags
-CFLAGS		+= -O0 -g
-# -MD -D__thumb2__=1
-#CFLAGS		+= -Wall -Werror -Wextra -Wshadow -Wimplicit-function-declaration
-#CFLAGS		+= -Wredundant-decls
-# -Wmissing-prototypes -Wstrict-prototypes
-CFLAGS		+= -fno-common 
-#-ffunction-sections -fdata-sections
+CFLAGS		+= -O2 -g -D__thumb2__=1 -MD
+CFLAGS		+= -Wall -Werror -Wextra -Wshadow 
+CFLAGS		+= -fno-common -ffunction-sections -fdata-sections
 
 ###############################################################################
 # Linker flags
-LDFLAGS		+= -nostartfiles
-# --static
-#--specs=nano.specs
+LDFLAGS		+= -nostartfiles --static
 LDFLAGS		+= -L$(LIB_DIR)
 LDFLAGS		+= -T$(LDSCRIPT)
-#LDFLAGS		+= -Wl,-Map=$(OBJDIR)/$(BINARY).map
-#LDFLAGS		+= -Wl,--gc-sections
 
 ###############################################################################
 # Used libraries
-#LDLIBS		+= -Wl,--start-group -lc -lgcc -Wl,--end-group 
-#LDLIBS		+= $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+LDLIBS		+= $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
 
 DEFS		+= -DSTM32$(FAMILY) -DSTM32$(MCU) -DSTM32F10X_$(DENSITY)
 
-#.SUFFIXES: .elf .bin .hex .srec .list .map .images
-#.SECONDEXPANSION:
-#.SECONDARY:
-
 ELF		:= $(OBJDIR)/$(BINARY).elf
 LIST	:= $(OBJDIR)/$(BINARY).list
 BIN		:= $(BINARY).bin
@@ -109,9 +97,6 @@ $(OBJDIR)/%.o: %.c
 	@echo "  CC      $<"
 	$(CC) $(CFLAGS) $(DEFS) $(INCLUDE) $(ARCH_FLAGS) -o $@ -c $<
 
-#$(OBJDIR)/%.d: %.c $(OBJDIR)
-#	$(CC) -MM -MG $< | sed -e 's,^\([^:]*\)\.o[ ]*:,$(@D)/\1.o $(@D)/\1.d:,' >$@
-
 $(BIN): $(ELF)
 	@echo "  OBJCOPY $(BIN)"
 	$(OBJCOPY) -Obinary $(ELF) $(BIN)
@@ -133,7 +118,7 @@ size: $(ELF)
 
 clean:
 	@echo "  CLEAN"
-	$(RM) $(OBJS) $(DEPS) $(ELF) $(HEX) $(LIST) $(OBJDIR)/*.map
+	$(RM) $(OBJS) $(DEPS) $(ELF) $(HEX) $(LIST)
 	@rmdir $(OBJDIR) 2>/dev/null || true
 
 
diff --git a/F1-nolib/led_blink/blink.bin b/F1-nolib/led_blink/blink.bin
index c3a87dd..879543f 100755
Binary files a/F1-nolib/led_blink/blink.bin and b/F1-nolib/led_blink/blink.bin differ
diff --git a/F1-nolib/led_blink/main.c b/F1-nolib/led_blink/main.c
index e3245f1..91b33ae 100644
--- a/F1-nolib/led_blink/main.c
+++ b/F1-nolib/led_blink/main.c
@@ -29,7 +29,7 @@ void sys_tick_handler(void){
 }
 
 // SysTick is 24 bit counter, so 16777215 - max value!!!
-// After HSE is ON it works @9MHz (????)
+// After HSE is ON it works @72MHz (or remove SysTick_CTRL_CLKSOURCE_Msk @ SysTick_Config for 8MHz)
 static void systick_setup(uint32_t xms){
     static uint32_t curms = 0;
     if(curms == xms) return;