add explanations

Author: PRosenb

cpp/arduino/AvrAdc.h

@@ -1,5 +1,9 @@
 #pragma once
 
-// mock storage to allow access to ADCSRA
+// ADCSRA is defined in the CPU specific header files
+// like iom328p.h.
+// It is liked to _SFR_MEM8 what does not exists in the test environment.
+// Therefore we define _SFR_MEM8 here and provide it a storage
+// location so that the test code can read/write on it.
 extern unsigned char sfr_store;
 #define _SFR_MEM8(mem_addr) sfr_store

cpp/arduino/avr/interrupt.h

@@ -1,6 +1,14 @@
+/*
+   This header file defines the macros required for the production
+   code for AVR CPUs to declare ISRs in the test environment.
+   See for more details
+   https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html
+*/
 #pragma once
 
-// allows the production code to define an ISR method
+// Allows the production code to define an ISR method.
+// These definitions come from the original avr/interrupt.h file
+// https://www.nongnu.org/avr-libc/user-manual/interrupt_8h_source.html
 #define _VECTOR(N) __vector_ ## N
 #define ISR(vector, ...)            \
      extern "C" void vector (void)  __VA_ARGS__; \

cpp/arduino/avr/sleep.h

@@ -1,3 +1,8 @@
+/*
+   This header file defines the functionality to put AVR CPUs to sleep mode.
+   For details see
+   https://www.nongnu.org/avr-libc/user-manual/group__avr__sleep.html
+*/
 #pragma once
 
 #include <Godmode.h>

cpp/arduino/avr/wdt.h

@@ -1,3 +1,9 @@
+/*
+   This header file defines the funtionality to use the watchdog timer on
+   AVR CPUs.
+   For details see
+   https://www.nongnu.org/avr-libc/user-manual/group__avr__watchdog.html
+*/
 #pragma once
 
 #include <Godmode.h>