diff --git a/firmware/hw_layer/digital_input_hw.cpp b/firmware/hw_layer/digital_input_hw.cpp
index b54d156c7c..6bb023227a 100644
--- a/firmware/hw_layer/digital_input_hw.cpp
+++ b/firmware/hw_layer/digital_input_hw.cpp
@@ -18,6 +18,7 @@
  *
  * rus084 is reminding that EXTI could be enough for our needs
  * See joystick.cpp
+ * See trigger_input.cpp
  *
  * @date Jun 23, 2013
  * @author Andrey Belomutskiy, (c) 2012-2018
@@ -271,4 +272,4 @@ void startInputDriver(digital_input_s *hw, bool isActiveHigh) {
 	hw->started = true;
 }
 
-#endif
+#endif /* EFI_WAVE_ANALYZER */
diff --git a/firmware/hw_layer/joystick.cpp b/firmware/hw_layer/joystick.cpp
index 4370487983..6e4c42efbf 100644
--- a/firmware/hw_layer/joystick.cpp
+++ b/firmware/hw_layer/joystick.cpp
@@ -9,6 +9,9 @@
  * be using same EXTI line. See https://stm32f4-discovery.net/2014/08/stm32f4-external-interrupts-tutorial/
  * See also comments in digital_input_hw.cpp
  *
+ *
+ * TODO: In release 18.2.0 the EXT driver is no more provided for STM32, there is a PAL demo under /testhal/STM32/multi/PAL with examples of callbacks and synchronous API.
+ *
  * @date Jan 2, 2015
  * @author Andrey Belomutskiy, (c) 2012-2018
  */
@@ -139,6 +142,7 @@ static uint32_t getExtMode(ioportid_t port) {
 	return 0;
 }
 
+// EXT is not able to give you the front direction but you could read the pin in the callback.
 static void enableExti(brain_pin_e pin, extcallback_t cb) {
 	if (pin == GPIO_UNASSIGNED)
 		return;
diff --git a/firmware/hw_layer/trigger_input.cpp b/firmware/hw_layer/trigger_input.cpp
index fb66757ddc..20a4dac37a 100644
--- a/firmware/hw_layer/trigger_input.cpp
+++ b/firmware/hw_layer/trigger_input.cpp
@@ -2,6 +2,12 @@
  * @file	trigger_input.cpp
  * @brief	Position sensor hardware layer
  *
+ * todo: code reuse with digital_input_hw.cpp was never finished
+ * todo: at the moment due to half-done code reuse we depend on EFI_WAVE_ANALYZER which makes no sense, need to finish this refactoring
+ * todo: VVT implementation is a nasty copy-paste :(
+ *
+ * see digital_input_hw.cp
+ *
  * @date Dec 30, 2012
  * @author Andrey Belomutskiy, (c) 2012-2018
  */