diff --git a/G4:G431/USB_CDC/main.c b/G4:G431/USB_CDC/main.c
index f5d5017..58a0070 100644
--- a/G4:G431/USB_CDC/main.c
+++ b/G4:G431/USB_CDC/main.c
@@ -35,7 +35,7 @@ int main(void){
     gpio_setup();
     usart_setup(115200);
     USB_setup();
-    bool pressed = false;
+    uint8_t pressed = 0;
     uint32_t Tblink = 0, Tkey = 0; // blink and key pressed time
     while(1){
         USART_flags_t f = usart_process();
@@ -56,7 +56,7 @@ int main(void){
         }
         if(KEY_PRESSED()){
             if(!pressed){ // new event
-                pressed = true;
+                pressed = 1;
                 usart_sendstr(spressed);
                 USB_putbyte('1'); USB_putbyte('1'); newline();
                 USB_sendstr(spressed);
@@ -64,7 +64,7 @@ int main(void){
             Tkey = Tms;
         }else{ // key released
             if(pressed && (Tms - Tkey) > TDEBOUNCE){ // wait for debounce
-                pressed = false;
+                pressed = 0;
                 usart_sendstr(sreleased);
                 USB_putbyte('0'); USB_putbyte('0'); newline();
                 USB_sendstr(sreleased);
diff --git a/G4:G431/USB_CDC/ringbuffer.c b/G4:G431/USB_CDC/ringbuffer.c
index 5e28ee0..9683f6c 100644
--- a/G4:G431/USB_CDC/ringbuffer.c
+++ b/G4:G431/USB_CDC/ringbuffer.c
@@ -31,9 +31,9 @@ int RB_datalen(ringbuffer *b){
     CHK(b);
     if(0 == datalen(b)) return 0; // don't block for empty RO operations
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int l = datalen(b);
-    b->busy = false;
+    b->busy = 0;
     return l;
 }
 
@@ -59,9 +59,9 @@ static int hasbyte(ringbuffer *b, uint8_t byte){
 int RB_hasbyte(ringbuffer *b, uint8_t byte){
     CHK(b);
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int ret = hasbyte(b, byte);
-    b->busy = false;
+    b->busy = 0;
     return ret;
 }
 
@@ -100,9 +100,9 @@ int RB_read(ringbuffer *b, uint8_t *s, int len){
     if(!s || len < 1) return -1;
     if(0 == datalen(b)) return 0;
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int r = read(b, s, len);
-    b->busy = false;
+    b->busy = 0;
     return r;
 }
 
@@ -136,14 +136,14 @@ int RB_readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len){
     if(!s || len < 1) return -1;
     if(0 == datalen(b)) return 0;
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int n = 0;
     if(s && len > 0){
         n = readto(b, byte, s, len);
     }else{
         incr(b, &b->head, lento(b, byte)); // just throw data out
     }
-    b->busy = false;
+    b->busy = 0;
     return n;
 }
 
@@ -151,9 +151,9 @@ int RB_datalento(ringbuffer *b, uint8_t byte){
     CHK(b);
     if(0 == datalen(b)) return 0;
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int n = lento(b, byte);
-    b->busy = false;
+    b->busy = 0;
     return n;
 }
 
@@ -184,9 +184,9 @@ int RB_write(ringbuffer *b, const uint8_t *str, int l){
     if(!str || l < 1) return -1;
     if(b->length - datalen(b) < 2) return 0;
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     int w = write(b, str, l);
-    b->busy = false;
+    b->busy = 0;
     return w;
 }
 
@@ -194,10 +194,10 @@ int RB_write(ringbuffer *b, const uint8_t *str, int l){
 int RB_clearbuf(ringbuffer *b){
     CHK(b);
     if(b->busy) return -1;
-    b->busy = true;
+    b->busy = 1;
     b->head = 0;
     b->tail = 0;
     memset(b->data, 0, b->length);
-    b->busy = false;
+    b->busy = 0;
     return 1;
 }
diff --git a/G4:G431/USB_CDC/ringbuffer.h b/G4:G431/USB_CDC/ringbuffer.h
index 8b7d808..5a0bf60 100644
--- a/G4:G431/USB_CDC/ringbuffer.h
+++ b/G4:G431/USB_CDC/ringbuffer.h
@@ -24,7 +24,7 @@ typedef struct{
     const int length;   // its length
     volatile int head;  // head index
     volatile int tail;  // tail index
-    volatile bool busy; // == TRUE if buffer is busy now
+    volatile uint8_t busy; // == TRUE if buffer is busy now
 } ringbuffer;
 
 int RB_read(ringbuffer *b, uint8_t *s, int len);
diff --git a/G4:G431/USB_CDC/usart.c b/G4:G431/USB_CDC/usart.c
index b1e7eff..a2754de 100644
--- a/G4:G431/USB_CDC/usart.c
+++ b/G4:G431/USB_CDC/usart.c
@@ -65,8 +65,8 @@ void dma1_channel2_isr() __attribute__ ((alias ("dmatx_isr")));
 #define DMARXCCR    (DMA_CCR_MINC | DMA_CCR_CIRC | DMA_CCR_TEIE)
 #define DMATXCCR    (DMA_CCR_MINC | DMA_CCR_DIR | DMA_CCR_TCIE | DMA_CCR_TEIE)
 
-static volatile bool gotstring = true; // got '\n' in input stream -> force data reading to inbuf
-static volatile bool txrdy = true; // Tx DMA not busy
+static volatile uint8_t gotstring = 1; // got '\n' in input stream -> force data reading to inbuf
+static volatile uint8_t txrdy = 1; // Tx DMA not busy
 static volatile USART_flags_t curflags; // current flags (cleared in `usart_process`)
 // rx/tx DMA buffers
 static uint8_t dmarxbuf[USARTRXDMABUFSZ];
@@ -123,19 +123,19 @@ void usart_setup(uint32_t speed){
  * @brief usart_sendbuf - send next data portion
  * @return true if sent something
  */
-static bool usart_sendbuf(){
-    if(!txrdy) return false;
+static uint8_t usart_sendbuf(){
+    if(!txrdy) return 0;
     int rd = RB_read(&TxRB, dmatxbuf, USARTTXDMABUFSZ);
-    if(rd < 1) return false; // nothing to write or busy
+    if(rd < 1) return 0; // nothing to write or busy
     // set up DMA
     DMACHTX->CCR = DMATXCCR;
     DMACHTX->CMAR = (uint32_t) dmatxbuf;
     DMACHTX->CNDTR = rd;
     USARTx->ICR = USART_ICR_TCCF; // clear TC flag
-    txrdy = false;
+    txrdy = 0;
     // activate DMA
     DMACHTX->CCR = DMATXCCR | DMA_CCR_EN;
-    return true;
+    return 1;
 }
 
 int usart_send(const char *str, int len){
@@ -235,7 +235,7 @@ char *usart_getline(){
 // interrupt by '\n'
 static void usart_isr(){
     if(USARTx->ISR & USART_ISR_CMF){ // got '\n' @ USARTx
-        gotstring = true;
+        gotstring = 1;
     }
     USARTx->ICR = 0xffffffff; // clear all flags
 }
@@ -251,7 +251,7 @@ static void dmarx_isr(){
 
 static void dmatx_isr(){
     volatile uint32_t isr = DMAx->ISR;
-    if(isr & DMATXTCF) txrdy = true;
+    if(isr & DMATXTCF) txrdy = 1;
     if(isr & DMATXEF) curflags.txerr = 1;
     DMAx->IFCR = DMATXTCF | DMATXEF; // clear all flags
 }
diff --git a/G4:G431/USB_CDC/usb_dev.c b/G4:G431/USB_CDC/usb_dev.c
index 2af95f9..ee7ed0e 100644
--- a/G4:G431/USB_CDC/usb_dev.c
+++ b/G4:G431/USB_CDC/usb_dev.c
@@ -21,6 +21,8 @@
 #include "usb_descr.h"
 #include "usb_dev.h"
 
+//#pragma GCC optimize ("O1")
+
 // Class-Specific Control Requests
 #define SEND_ENCAPSULATED_COMMAND       0x00    // unused
 #define GET_ENCAPSULATED_RESPONSE       0x01    // unused
diff --git a/G4:G431/USB_CDC/usbcdc.bin b/G4:G431/USB_CDC/usbcdc.bin
index a8e191a..43f602b 100755
Binary files a/G4:G431/USB_CDC/usbcdc.bin and b/G4:G431/USB_CDC/usbcdc.bin differ
diff --git a/makefile.stm32 b/makefile.stm32
index ef9a466..2880721 100644
--- a/makefile.stm32
+++ b/makefile.stm32
@@ -49,7 +49,7 @@ LIB_DIR		:= $(INC_DIR)/ld
 
 ###############################################################################
 # C flags
-CFLAGS		+= -D__thumb2__=1 -MD
+CFLAGS		+= -D__thumb2__=1 -MD 
 CFLAGS		+= -Wall -Wextra -Wshadow -Wdouble-promotion
 CFLAGS		+= -fshort-enums -ffunction-sections -fdata-sections
 #CFLAGS		+= -fno-common -fno-stack-protector
@@ -57,12 +57,12 @@ CFLAGS		+=  $(ARCH_FLAGS)
 
 ###############################################################################
 # Linker flags
-LDFLAGS		+= -nostartfiles --static -specs=nosys.specs -specs=nano.specs
+LDFLAGS		+= -nostartfiles --static -specs=nano.specs
 LDFLAGS		+= $(ARCH_FLAGS)
 LDFLAGS		+= -L$(LIB_DIR) 
 #-L$(TOOLCHLIB)
 LDFLAGS		+= -T$(LDSCRIPT)
-LDFLAGS		+= -Wl,-Map=$(MAP),--cref -Wl,--gc-sections -Wl,--print-memory-usage
+LDFLAGS		+= -Wl,-Map=$(MAP),--cref -Wl,--gc-sections -Wl,--print-memory-usage -Wl,--trace-symbol=_sbrk 
 
 ###############################################################################
 # Used libraries
@@ -102,6 +102,8 @@ debug: CFLAGS += -O0 -DEBUG -Werror -g3 -gdwarf-2
 debug: TARGET := DEBUG
 debug: $(TARGFILE) bin list size
 
+all: $(BIN)
+
 $(TARGFILE): $(OBJDIR)
 	@echo -e "\t\tTARGET: $(TARGET)"
 	@echo "$(TARGET)" > $(TARGFILE)
@@ -130,13 +132,15 @@ $(VERSION_FILE): *.[ch]
 
 $(OBJDIR)/proto.o: proto.c $(VERSION_FILE)
 
+$(OBJDIR)/usb_dev.o: CFLAGS := $(filter-out -flto,$(CFLAGS)) -fno-lto
+
 $(OBJDIR)/%.o: %.c
 	@echo "  CC      $<"
 	$(CC) $(CFLAGS) $(DEFS) $(INCLUDE) -o $@ -c $<
 
 $(OBJDIR)/%.o: %.cpp
 	@echo "  C++     $<"
-	$(CPP) -c $(CFLAGS) -fno-exceptions $(DEFS) $(INCLUDE) -o $@ -c $<
+	$(CPP) -c $(CFLAGS) -std=c++11 -fno-exceptions -fno-rtti -Wl,--trace-symbol=_sbrk $(DEFS) $(INCLUDE) -o $@ -c $<
 
 $(BIN): $(ELF)
 	@echo "  OBJCOPY $(BIN)"