Improved my answers in tinming_resources

examples/timing_resources.rs

@@ -83,6 +83,11 @@ const APP: () = {
 //  msr	basepri, r0 = Writes the value of r0 into coprocessor register basepri.
 //  bx	lr = 
 // 
+//  The function starts by loading the priority celling into registry r0.
+//  Then it loads in the shared variable into register r2.
+//  Then it add one to the shared variable(r1).
+//  Then it sets the shared variable.
+//  Lastly it sets the priority celling back to what it was before.
 //
 //
 // > cargo run --example timing_resources --release --features nightly
@@ -103,7 +108,7 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000010
+// 0xe0001004:	0x00000010 = 16 cycles
 //
 // (gdb) disassemble
 //
@@ -129,12 +134,12 @@ const APP: () = {
 // What was the software latency observed to enter the task?
 //
 // [Your answer here]
-// 16 - 2 = 14
+// 16 - 2 = 14 cycles
 //
 // Does RTIC infer any overhead?
 //
 // [Your answer here]
-// Yes, it add 2 cycles. Because Cortex-M4 interupt takes 12 cycles.
+// Yes, it add 2 cycles of overhead. Cortex-M4 interupt takes 12 cycles.
 //
 // The debugger reports that the breakpoint was hit in the `run<closure>`.
 // The reason is that the RTIC implements the actual interrupt handler,
@@ -153,7 +158,7 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000025
+// 0xe0001004:	0x00000025 = 32 + 5 = 37 cycles
 //
 // You should have a total execution time in the range of 30-40 cycles.
 //
@@ -161,7 +166,9 @@ const APP: () = {
 // `exti0` was safe without locking the resource.
 //
 // [Your answer here]
-// TODO
+// I think the reason is that EXTI0 has a higher priorety then EXTI1 which means that EXTI0 will
+// never be interupted by EXTI1. And EXTI0 can never interupt EXTI1 when it is using the shared
+// variable becaise EXTI1 uses a lock. 
 //
 // In `exti1` we also access `shared` but this time through a lock.
 //
@@ -191,12 +198,12 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000034
+// 0xe0001004:	0x00000034 = 32 + 16 + 4 = 52 cycles
 //
 // Calculate the total time (in cycles), for this section of code.
 //
 // [Your answer here]
-// 52 - 37 = 15
+// 52 - 37 = 15 cycles
 //
 // You should get a value around 15 cycles.
 //
@@ -237,7 +244,7 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000028
+// 0xe0001004:	0x00000028 = 32 + 8 = 40 cycles
 //
 // (gdb) c
 //
@@ -248,7 +255,7 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000032
+// 0xe0001004:	0x00000032 = 32 + 16 + 2 = 50 cycles
 //
 // From a real-time perspective the critical section infers
 // blocking (of higher priority tasks).
@@ -256,7 +263,7 @@ const APP: () = {
 // How many clock cycles is the blocking?
 //
 // [Your answer here]
-// 50 - 40 = 10
+// 50 - 40 = 10 cycles
 //
 // Finally continue out of the closure.
 //
@@ -267,7 +274,7 @@ const APP: () = {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
-// 0xe0001004:	0x00000034
+// 0xe0001004:	0x00000034 = 32 + 16 + 4 = 52 cycles
 //
 // This is the total execution time of:
 //
@@ -291,7 +298,19 @@ const APP: () = {
 // Motivate your answer (not just a number).
 //
 // [Your answer here]
-// TODO
+// Estimated cost per task:
+//   Pending the task EXTI1 cost 650 cycles (job latency).
+//   Starting the thread EXTI1 cost 1522 cycles (job overhead).
+//   Pending the task EXTI0 cost 650 cycles (job latency).
+//   Starting the thread EXTI0 cost 1522 cycles (job overhead).
+//   Locking the shared variable cost 260 cycles ().
+//   Unlocking the shared variable cost 170 cycles ().
+//   Returning to EXTI1 cost 1522 cycles (job overhead).
+//   Locking the shared variable cost 260 cycles ().
+//   Unlocking the shared variable cost 170 cycles ().
+//
+//
+// The total cost: 650 + 1522 + 650 + 1522 + 260 + 170 + 1522 + 260 + 170 = 6726
 //
 // Notice, the Rust implementation is significantly faster than the C code version
 // of Real-Time For the Masses back in 2013.