bare5_2

examples/bare5.rs

@@ -13,6 +13,7 @@ extern crate panic_halt;
 
 extern crate cortex_m;
 use cortex_m_rt::entry;
+use cortex_m_semihosting::{hprint, hprintln};
 
 // C like API...
 mod stm32f40x {
@@ -56,13 +57,21 @@ mod stm32f40x {
     // offset (field offset)
     // width  (field width)
     // value  (new value that the field should take)
-    //
-    // impl VolatileCell<u32> {
-    //     #[inline(always)]
-    //     pub fn modify(&self, offset: u8, width: u8, value: u32) {
-    //         // your code here
-    //     }
-    // }
+    impl VolatileCell<u32> {
+        #[inline(always)]
+        pub fn modify(&self, offset: u8, width: u8, value: u32) {
+            let mask: u32 = 2u32.pow(width as u32) - 1; // 'width' amount of binary 1s.
+
+            // Mask the input
+            let in_masked: u32 = value & mask;
+
+            // Mask the previous value
+            let previous: u32 = self.read();
+            let previous_masked: u32 = previous & !(mask * 2u32.pow(offset as u32));
+
+            self.write(previous_masked | (in_masked * 2u32.pow(offset as u32)));
+        }   
+    }   
 
     #[repr(C)]
     #[allow(non_snake_case)]
@@ -151,15 +160,17 @@ fn wait(i: u32) {
 //     //    ..0111000
 //     //    ---------
 //     //    000101000
+//     hprintln!("{:b}", t.read()).unwrap();
 //     assert!(t.read() == 0b101 << 3);
 //     t.modify(4, 3, 0b10001);
 //     //    000101000
 //     //      111
 //     //      001
 //     //    000011000
+//     hprintln!("{:b}", t.read()).unwrap();
 //     assert!(t.read() == 0b011 << 3);
 
-// if << is used, your code will panic in dev (debug), but not in release mode
+//     // if << is used, your code will panic in dev (debug), but not in release mode
 //     t.modify(32, 3, 1);
 // }
 
@@ -177,23 +188,30 @@ fn main() -> ! {
 // user application
 fn idle(rcc: &mut RCC, gpioa: &mut GPIOA) {
     // power on GPIOA
-    let r = rcc.AHB1ENR.read(); // read
-    rcc.AHB1ENR.write(r | 1 << (0)); // set enable
+    rcc.AHB1ENR.modify(0u8, 1u8, 1u32);
+    // let r = rcc.AHB1ENR.read(); // read
+    // rcc.AHB1ENR.write(r | 1 << (0)); // set enable
 
     // configure PA5 as output
-    let r = gpioa.MODER.read() & !(0b11 << (5 * 2)); // read and mask
-    gpioa.MODER.write(r | 0b01 << (5 * 2)); // set output mode
-
+    gpioa.MODER.modify(10u8, 2u8, 1u32);
+    // let r = gpioa.MODER.read() & !(0b11 << (5 * 2)); // read and mask
+    // gpioa.MODER.write(r | 0b01 << (5 * 2)); // set output mode
+    let led_odr = &gpioa.ODR;
     loop {
         // set PA5 high
+        // gpioa.ODR.modify(5u8, 1u8, 1u32);
+        led_odr.modify(5u8, 1u8, 1u32);
+
         // gpioa.BSRRH.write(1 << 5); // set bit, output hight (turn on led)
-        gpioa.ODR.write(gpioa.ODR.read() | (1 << 5));
+        // gpioa.ODR.write(gpioa.ODR.read() | (1 << 5));
 
         wait(10_000);
 
         // set PA5 low
+        // gpioa.ODR.modify(5u8, 1u8, 0u32);
+        led_odr.modify(5u8, 1u8, 0u32);
         // gpioa.BSRRL.write(1 << 5); // clear bit, output low (turn off led)
-        gpioa.ODR.write(gpioa.ODR.read() & !(1 << 5));
+        // gpioa.ODR.write(gpioa.ODR.read() & !(1 << 5));
         wait(10_000);
     }
 }
@@ -243,3 +261,10 @@ fn idle(rcc: &mut RCC, gpioa: &mut GPIOA) {
 //    Notice, over-shifting (where bits are spilled) is always considered legal,
 //    its just the shift amuount that is checked.
 //    There are explicit unchecked versions available if so wanted.
+// 
+//      ** ORDERING IS WRONG FOR OPTIMIZED CODE **
+//      When I run the --release build, the LED is constantly turned on. HOWEVER,
+//      if I set breakpoints and pause in the --release build, I can pause it
+//      just after the LED-turn-off call and the LED turns off, proving that the
+//      instructions work in release as they do in debug, but that it doesn't wait
+//      before running the turn-on call as it should.
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