timing_resources, Q1: EXTI0 explanation

examples/timing_resources.rs

@@ -72,6 +72,26 @@ const APP: () = {
 // Explain what is happening here in your own words.
 //
 // [Your code here]
+/*
+Tl;dr, 
+1. Saves privious basepri, and stops at our breakpoint
+2. Loads our shared resource from memmory
+3. Increment resource by 1 and save it back to memory
+4. Changes back basepri to what it was before
+5. Branches back to where we were before the exception.
+
+08000232 <EXTI0>:
+ 8000232: 40 f2 00 01  	movw	r1, #0      // Loads 0 into r1
+ 8000236: ef f3 11 80  	mrs	r0, basepri     // Save the current basepri into r0
+ 800023a: 00 be        	bkpt	#0          // Breakpoint here                                          <-- Our interupt code begins here
+ 800023c: c2 f2 00 01  	movt	r1, #8192   // Puts 0x2000 into top 16-bits of r1 => 0x20000000 (The location of the shared resource, maybe also the begining of our memory)
+ 8000240: d1 e9 00 23  	ldrd	r2, r3, [r1]// Equivalent to: ldr r2, [r1]; ldr r3, [r1, #4], ie loads the bottom half of the shared resource into r2 and the top half into r3
+ 8000244: 01 32        	adds	r2, #1      // Add 1 to r2, update flag (N, Z, C, V ie carry flags etc) <-- Increments our shared resource with 1
+ 8000246: 43 f1 00 03  	adc	r3, r3, #0      // Add 0 to r3 (with carry)                                 <-- Add the carry if we have carry from last operation
+ 800024a: c1 e9 00 23  	strd	r2, r3, [r1]// Saves back our shared resource into main memory          <-- Our interupt code stops here
+ 800024e: 80 f3 11 88  	msr	basepri, r0     // Changes the basepri to what it was before
+ 8000252: 70 47        	bx	lr              // Branches back to where we were before
+*/
 //
 // > cargo run --example timing_resources --release --features nightly
 // Then continue to the first breakpoint instruction: