Done

compile.sh

@@ -7,4 +7,5 @@
 #cargo build --target thumbv7em-none-eabihf --release --example bare2
 #cargo build --target thumbv7em-none-eabihf --example bare3
 #cargo build --target thumbv7em-none-eabihf --example bare4
-cargo build --target thumbv7em-none-eabihf --example bare5
+#cargo build --target thumbv7em-none-eabihf --example bare5
+cargo build --target thumbv7em-none-eabihf --example bare6

examples/bare6.rs

@@ -6,6 +6,7 @@
 
 extern crate f4;
 extern crate stm32f40x;
+extern crate cortex_m;
 
 #[macro_use]
 extern crate cortex_m_debug;
@@ -76,7 +77,11 @@ fn idle(dwt: &mut DWT, rcc: &mut RCC, gpioa: &mut GPIOA) {
 
     // at 16 Mhz, 8000_0000 cycles = 0.5s
     // at 64 Mhz, 8000_0000 cycles = 0.125s
+    unsafe { 
+        (*DWT.get()).cyccnt.write(0);
+    }
     loop {
+        
         ipln!("led on");
         // set PA5 high, RM0368 8.4.7
         gpioa.bsrr.write(|w| w.bs5().set_bit());
@@ -100,6 +105,10 @@ fn idle(dwt: &mut DWT, rcc: &mut RCC, gpioa: &mut GPIOA) {
 // vscode using the new "cortex debug" plugin
 //
 // what is the frequency of blinking
+//
+//  >> Given that at 16Mhz, 8000_000 cycles = 0.5s,
+//      and we need to go 2*8000_000 cycles for the next light on,
+//      we're about ~1Hz on the blinking, just slightly above.
 // ** your answer here **
 //
 // commit your answers (bare6_1)

gdb.sh

@@ -8,4 +8,4 @@ TARGET=thumbv7em-none-eabihf
 #arm-none-eabi-gdb target/$TARGET/release/examples/bare2
 #arm-none-eabi-gdb target/$TARGET/debug/examples/bare3
 #arm-none-eabi-gdb target/$TARGET/debug/examples/bare4
-arm-none-eabi-gdb target/$TARGET/debug/examples/bare5
+arm-none-eabi-gdb target/$TARGET/debug/examples/bare6