diff --git a/Makefile b/Makefile
index 6a89cf5..ec201a4 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ VPATH  = . ./$(TARGET)
 
 # zdrojaky -> objekty
 OBJS   = STM32L4x2_startup.o system.o
-MOBJS  = main.o io.o
+MOBJS  = main.o io.o sys.o
 
 BOBJS  = $(addprefix $(BLD),$(OBJS))
 
@@ -48,7 +48,7 @@ $(BLD)%.o: %.cpp
 $(BLD):
 	mkdir $(BLD)
 # MODULES #
-main.o: main.cpp io.pcm
+main.o: main.cpp io.pcm sys.pcm
 %.o: %.cpp
 	-@echo [CXM $(TARGET)] $@
 	@$(CXX) $(VFLAGS) -c $(MFLAGS) $< -o $@
diff --git a/io.cpp b/io.cpp
index 6ca90b5..d0e042b 100644
--- a/io.cpp
+++ b/io.cpp
@@ -179,8 +179,4 @@ namespace io {
     RCC.AHB2ENR.R |= cPortTab[port].clkMask;
     setMode  (type);
   }
-  export void wait (const unsigned ms = 500000u) {
-    volatile unsigned n;
-    for (n=0u; n<ms; n+=1) asm volatile ("nop");
-  }
 };
diff --git a/main.cpp b/main.cpp
index 1138f5b..6c7fe2c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,12 +1,14 @@
 /*   SIMPLE EXAMPLE: LED blinking   */
 import io;           // use module !!!
+import sys;
 //////////////////////////////////////
 static io::GpioClass led (GpioPortA, 10);
 
 int main () {
+  sys::init ();
   for (;;) {
     ~led;         // change status - unary ~
-    io::wait ();
+    sys::delay ();
   }
   return 0;
 }
diff --git a/sys.cpp b/sys.cpp
new file mode 100644
index 0000000..29db9f9
--- /dev/null
+++ b/sys.cpp
@@ -0,0 +1,22 @@
+module;
+#include "CortexM4.h"
+#include "system.h"
+export module sys;
+
+static volatile unsigned count = 0u;
+extern "C" void SysTick_Handler () {
+  if (count) count -= 1u;
+}
+namespace sys {
+  export void delay (const unsigned ms = 500) {
+    count = ms;
+    while (count) {
+      asm volatile ("wfi");
+    }
+  }
+  export void init () {
+    EnableDebugOnSleep();
+    SysTick.Config (SystemCoreClock / 1000u);
+  }
+};
+