bare1_5

examples/rtic_bare1.rs

@@ -20,9 +20,9 @@ const APP: () = {
     fn init(_cx: init::Context) {
         let mut x = core::u32::MAX - 1;
         loop {
-            // cortex_m::asm::bkpt();
-            x += 1;
-            // cortex_m::asm::bkpt();
+            cortex_m::asm::bkpt();
+            x = x.wrapping_add(1);
+            cortex_m::asm::bkpt();
 
             // prevent optimization by read-volatile (unsafe)
             unsafe {
@@ -138,13 +138,13 @@ const APP: () = {
 //
 //    Explain in your own words what this assembly line does.
 //
-//    ** your answer here **
+//    load the value of the address sp + offset 0 to register address r0
 //
 //    In Cortex Registers (left) you can see the content of `r0`
 //
 //    What value do you observe?
 //
-//    ** your answer here **
+//    -2 (MAX-2)
 //
 //    You can also get the register info from GDB directly.
 //
@@ -162,7 +162,7 @@ const APP: () = {
 //
 //    Explain in your own words what is happening here.
 //
-//    ** your answer here **
+//    add to the register r0 the immidiate constant 1
 //
 //    We move to the next assembly instruction:
 //
@@ -171,7 +171,7 @@ const APP: () = {
 //
 //    What is the reported value for `r0`
 //
-//    ** your answer here **
+//    -1 (MAX) (0xffffffff)
 //
 //    So far so good.
 //
@@ -202,7 +202,7 @@ const APP: () = {
 //
 //    What does BCS do?
 //
-//    ** your answer here **
+//    BCS.n branches if there was a carry bit from the last addition. (.n makes the instruction to be 16 bits)
 //
 //    Now let's see what happens.
 //
@@ -216,7 +216,7 @@ const APP: () = {
 //
 //    Explain in your own words where we are heading.
 //
-//    ** your answer here **
+//    We are heading toward a branch to the panic "function"
 //
 //    To validate that your answer, let's let the program continue
 //
@@ -232,7 +232,7 @@ const APP: () = {
 //    Hint 3, the code is generated by the Rust compiler to produce the error message.
 //            there is no "magic" here, just a compiler generating code...
 //
-//    ** your answer here **
+//    it is to generate the error message.
 //
 //    Commit your answer (bare1_4)
 //
@@ -285,7 +285,7 @@ const APP: () = {
 //
 //    Do you see any way this code may end up in a panic?
 //
-//    ** your answer here **
+//    No since there is no branching when there is a carry.
 //
 //    So clearly, the "semantics" (meaning) of the program has changed.
 //    This is on purpose, Rust adopts "unchecked" (wrapping) additions (and subtractions)
@@ -300,16 +300,32 @@ const APP: () = {
 //
 //    Paste the generated assembly:
 //
-//    ** your answer here **
+//    0x08000e84 <+0>:	push	{r4, r6, r7, lr}
+//    0x08000e86 <+2>:	add	r7, sp, #8
+//    0x08000e88 <+4>:	sub	sp, #16
+//    0x08000e8a <+6>:	movw	r0, #5808	; 0x16b0
+//    0x08000e8e <+10>:	mov	r4, sp
+//    0x08000e90 <+12>:	movt	r0, #2048	; 0x800
+//    0x08000e94 <+16>:	ldr	r0, [r0, #0]
+//    0x08000e96 <+18>:	str	r0, [sp, #0]
+//    0x08000e98 <+20>:	bl	0x8000fa6 <lib::__bkpt>
+// => 0x08000e9c <+24>:	ldr	r0, [sp, #0]
+//    0x08000e9e <+26>:	adds	r0, #1
+//    0x08000ea0 <+28>:	str	r0, [sp, #0]
+//    0x08000ea2 <+30>:	bl	0x8000fa6 <lib::__bkpt>
+//    0x08000ea6 <+34>:	mov	r0, r4
+//    0x08000ea8 <+36>:	bl	0x8000f46 <_ZN4core3ptr13read_volatile17hb977623ea709e27cE>
+//    0x08000eac <+40>:	b.n	0x8000e98 <rtic_bare1::init+20>
 //
 //    Can this code generate a panic?
 //
-//    ** your answer here **
+//    No, no branch to a panic "function"
 //
 //    Is there now any reference to the panic handler?
 //    If not, why is that the case?
 //
-//    ** your answer here **
+//    There is no reference since there is no need for it as we have stated that
+//      wrapping is the intended outcome
 //
 //    commit your answers (bare1_5)
 //