rtt_timing E

.cargo/config

@@ -6,9 +6,9 @@
 # uncomment ONE of these three option to make `cargo run` start a GDB session
 # which option to pick depends on your system
 # runner = "arm-none-eabi-gdb -q -x openocd.gdb"
-# runner = "gdb-multiarch -q -x openocd.gdb"
+runner = "gdb-multiarch -q -x openocd.gdb"
 # runner = "gdb -q -x openocd.gdb"
-runner = "probe-run --chip STM32F411RETx"
+# runner = "probe-run --chip STM32F411RETx"
 
 rustflags = [
   # This is needed if your flash or ram addresses are not aligned to 0x10000 in memory.x

examples/rtt_timing.rs

@@ -102,7 +102,7 @@ fn timed_loop() -> (u32, u32) {
 // Why do you think it differs that much?
 //
 // [Your answer here]
-// I think that the optimizer removed the for loop:
+// I think that the optimizer removes the for loop:
 //      for _ in 0..10000 {
 //          asm::nop();
 //      }
@@ -234,11 +234,45 @@ fn timed_loop() -> (u32, u32) {
 // https://developer.arm.com/documentation/ddi0439/b/Data-Watchpoint-and-Trace-Unit/DWT-Programmers-Model
 //
 // [Your answer here]
+// No, there is no function call. The two following line loads in the loaction of the cycle count,
+// which is always updated. Thus r1 holds the location of the cycle counter.
+// 0x08000232 <+0>:     movw    r1, #4100       ; 0x1004
+// 0x0800023a <+8>:     movt    r1, #57344      ; 0xe000
+// Then the two following lines loads in the current cycle value for start(r0) and end(r1).
+// 0x0800023e <+12>:    ldr     r0, [r1, #0]
+// 0x08000246 <+20>:    ldr     r1, [r1, #0]
+//
 //
 // Now check your answer by dumping the registers
 // (gdb) info registers
 //
 // [Register dump here]
+// (gdb) info registers
+// r0             0x80000000          -2147483648
+// r1             0xe0001004          -536866812
+// r2             0x2710              10000
+// r3             0xa                 10
+// r4             0x20000000          536870912
+// r5             0x20000430          536871984
+// r6             0x0                 0
+// r7             0x2000ffe8          536936424
+// r8             0x0                 0
+// r9             0x0                 0
+// r10            0x0                 0
+// r11            0x0                 0
+// r12            0x1                 1
+// sp             0x2000ff98          0x2000ff98
+// lr             0x8000373           134218611
+// pc             0x800023e           0x800023e <rtt_timing::timed_loop+12>
+// xPSR           0x81000000          -2130706432
+// fpscr          0x0                 0
+// msp            0x2000ff98          0x2000ff98
+// psp            0x0                 0x0
+// primask        0x1                 1
+// basepri        0x0                 0
+// faultmask      0x0                 0
+// control        0x0                 0
+// 
 //
 // We can now set a breakpoint exactly at the `nop`.
 //
@@ -264,6 +298,7 @@ fn timed_loop() -> (u32, u32) {
 // (gdb) x 0xe0001004
 //
 // [Your answer here]
+// 0x31de3cd8
 //
 // Now, let's execute one iteration:
 // (gdb) continue
@@ -271,10 +306,12 @@ fn timed_loop() -> (u32, u32) {
 // What is now the current value of the cycle counter?
 //
 // [Your answer here]
+// 0x31de3cdc
 //
 // By how much does the cycle counter increase for each iteration?
 //
 // [Your answer here]
+// 4
 //
 // ------------------------------------------------------------------------
 // F) Reseting the cycle counter