Did my best

examples/rtic_bare5.rs

-//! bare5.rs
+//! rtic_bare5.rs
 //!
 //! C Like Peripheral API
 //!
@@ -11,6 +11,7 @@
 
 extern crate cortex_m;
 extern crate panic_semihosting;
+//use bitvec::prelude::*; <-- Might wont to look in to this.
 
 // C like API...
 mod stm32f40x {
@@ -58,7 +59,9 @@ mod stm32f40x {
     impl VolatileCell<u32> {
         #[inline(always)]
         pub fn modify(&self, offset: u8, width: u8, value: u32) {
-            // your code here
+            let mut value_mut = value << 32-width;
+            value_mut = value_mut >> 32-width;
+            self.write(value_mut << offset);
         }
     }
 
@@ -177,32 +180,31 @@ const APP: () = {
         let r = gpioa.MODER.read() & !(0b11 << (5 * 2)); // read and mask
         gpioa.MODER.write(r | 0b01 << (5 * 2)); // set output mode
 
+        // test_modify();
+        test_modify();
+
         loop {
             // set PA5 high
-            gpioa.BSRRH.write(1 << 5); // set bit, output hight (turn on led)
+            //gpioa.BSRRH.write(1 << 5); // set bit, output hight (turn on led)
 
             // alternatively to set the bit high we can
             // read the value, or with PA5 (bit 5) and write back
-            // gpioa.ODR.write(gpioa.ODR.read() | (1 << 5));
+             gpioa.ODR.write(gpioa.ODR.read() | (1 << 5));
 
             wait(10_000);
 
             // set PA5 low
-            gpioa.BSRRL.write(1 << 5); // clear bit, output low (turn off led)
+            //gpioa.BSRRL.write(1 << 5); // clear bit, output low (turn off led)
 
             // alternatively to clear the bit we can
             // read the value, mask out PA5 (bit 5) and write back
-            // gpioa.ODR.write(gpioa.ODR.read() & !(1 << 5));
+             gpioa.ODR.write(gpioa.ODR.read() & !(1 << 5));
             wait(10_000);
         }
     }
 };
 
-// 0. Build and run the application.
-//
-//    > cargo build --example bare5
-//    (or use the vscode)
-//
+
 // 1. C like API.
 //    Using C the .h files are used for defining interfaces, like function signatures (prototypes),
 //    structs and macros (but usually not the functions themselves).
@@ -211,9 +213,8 @@ const APP: () = {
 //    provided by ST (and other companies). Actually, the file presented here is mostly a
 //    cut/paste/replace of the stm32f40x.h, just Rustified.
 //
-//
 //    In the loop we access PA5 through bit set/clear operations.
-//    Comment out those operations and uncomment the the ODR accesses.
+//    Comment out those operations and uncomment the ODR based accesses.
 //    (They should have the same behavior, but is a bit less efficient.)
 //
 //    Run and see that the program behaves the same.
@@ -228,12 +229,10 @@ const APP: () = {
 //
 //    Implement and check that running `test` gives you expected behavior.
 //
-//    Change the code into using your new API.
+//    Change the code into using your new `modify` API.
 //
 //    Run and see that the program behaves the same.
 //
-//    Commit your answers (bare5_2)
-//
 //    Discussion:
 //    As with arithmetic operations, default semantics differ in between
 //    debug/dev and release builds.
@@ -247,4 +246,6 @@ const APP: () = {
 //    What if we could automatically generate that from Vendors specifications (SVD files)?
 //    Wouldn't that be great?
 //
-//    ** your answer here **
+//    I got the first assert to work. But I don't understand the second. What are we supposed to do?
+//
+//    Commit your answers (bare5_2)