bare 4_3

examples/bare4.rs

@@ -116,13 +116,15 @@ fn main() -> ! {
 //      
 //      error: aborting due to previous error
 // 
-//      Reading adresses is not safe so it panics 
+//      read_voliatile is a unsafe so it panics 
 //
 //    Digging a bit deeper, why do you think `read_volatile` is declared `unsafe`.
 //    (https://doc.rust-lang.org/core/ptr/fn.read_volatile.html, for some food for thought )
 //
 //    ** your answer here **
-//
+//      
+//      because rust cant guarantee to know whats on the memmory address 
+// 
 //    Commit your answers (bare4_2)
 //
 // 3. Volatile read/writes are explicit *volatile operations* in Rust, while in C they
@@ -135,15 +137,31 @@ fn main() -> ! {
 //    Why is it important that ordering of volatile operations are ensured by the compiler?
 //
 //    ** your answer here **
+// 
+//       because volatile just reads the momory address so if it is done in the wrong order it 
+//       might read values that are wrong and the use them.
 //
 //    Give an example in the above code, where reordering might make things go horribly wrong
 //    (hint, accessing a peripheral not being powered...)
 //
 //    ** your answer here **
-//
+// 
+//        // power on GPIOA
+//      let r = read_u32(RCC_AHB1ENR); // read
+//      write_u32(RCC_AHB1ENR, r | 1); // set enable
+// 
+//      //configure PA5 as output
+//      let r = read_u32(GPIOA_MODER) & !(0b11 << (5 * 2)); // read and mask
+//      write_u32(GPIOA_MODER, r | 0b01 << (5 * 2)); // set output mode
+//          
+//      if poweron giopa would happen after the config it could cause problems
+//          
 //    Without the non-reordering property of `write_volatile/read_volatile` could that happen in theory
 //    (argue from the point of data dependencies).
 //
 //    ** your answer here **
+// 
+//          its important that they are non-reordering because otherwise if a write_volitile is dependent on data from a read_volitile
+//          and its reorderd it would not have all the relevent data it needs.
 //
 //    Commit your answers (bare4_3)