add comments

src/main.rs

@@ -5,19 +5,33 @@
 use core::arch::asm;
 use core::ptr::{read_volatile, write_volatile};
 
+/*
+PORTC{0..5} Analog
+PORTC6 Reset
+
+PORTB{0..5} Digital {8..13}
+PORTD{0..7} Digital {0..7}
+
+PORTB5 LED_BUILTIN
+ */
+
 const DDRB: *mut u8 = 0x24 as *mut u8;
 const PORTB: *mut u8 = 0x25 as *mut u8;
 
+// ATmega328p cycle speed
 const CPU_SPEED: u32 = 16_000_000;
 
 #[no_mangle]
 pub extern "C" fn main() -> ! {
+    // Set all the B pins on OUTPUT mode
     unsafe { write_volatile(DDRB, 0b11111111) };
 
     loop {
-        unsafe { write_volatile(PORTB, 0b00000000) };
+        // if pin[5] == 1: 1^1 = 0
-        sleep(1);
+        // if pin[5] == 0: 0^1 = 1
-        unsafe { write_volatile(PORTB, 0b00100000) };
+        let mut portb_value = unsafe { read_volatile(PORTB) };
+        portb_value = portb_value ^ (1 << 5);
+        unsafe { write_volatile(PORTB, portb_value) };
         sleep(1);
     }
 }