Exercise A

examples/rtt_timing.rs

@@ -45,7 +45,7 @@ const APP: () = {
 #[no_mangle]
 fn timed_loop() -> (u32, u32) {
     let start = DWT::get_cycle_count();
-    for _ in 0..10000 {
+    for _ in 0..1000 {
         asm::nop();
     }
     let end = DWT::get_cycle_count();
@@ -63,15 +63,15 @@ fn timed_loop() -> (u32, u32) {
 // A.1) What is the cycle count for the loop?
 // > cargo run --example rtt_timing
 //
-// [Your answer here]
+// [The loop in timed_loop is looping 335424926-330634772 = 4790154 times]
 //
 // A.2) How many cycles per iteration?
 //
-// [Your answer here]
+// [4790154/1000 = 4790]
 //
 // A.3) Why do we need a wrapping subtraction?
 //
-// [Your answer here]
+// [Becasue the variable is a unsigned 32 bit int, which will overflow when taking substraction bit wise. Therefore a wrapper is there to make sure the substraction is correctly calculated even if it overflow.]
 //
 // ------------------------------------------------------------------------
 // Now try a release (optimized build, see `Cargo.toml` for build options).