docs

firmware/hw_layer/digital_input_hw.cpp

@@ -2,6 +2,21 @@
  * @file	digital_input_hw.cpp
  * @brief	Helper methods related to Input Capture Unit (ICU)
  *
+ * There are some ChibiOS limitation or STM32 limitations or limitations of my brain
+ *
+ * See http://www.chibios.com/forum/viewtopic.php?t=1461
+ *    "PWM input requires a whole timer on the STM32.
+ *    You could use channel 1 and channel 2 of the same timer but not simultaneously.
+ *    Giovanni"
+ *
+ * See http://www.chibios.com/forum/viewtopic.php?f=2&t=247&hilit=icu+channel&start=50
+ *    "It is not possible, the TIM timers support one ICU channel at time.
+ *    Giovanni"
+ *
+ * See https://stackoverflow.com/questions/43440599/stm32-multi-channel-input-capture-overcapturing-on-all-channels-interrupts-not
+ *    where they seem to be capturing something on multiple channels maybe not PWM mode of ICU is the key difference?
+ *
+ *
  * @date Jun 23, 2013
  * @author Andrey Belomutskiy, (c) 2012-2018
  */