implement timer

src/main.rs

@@ -5,8 +5,10 @@
 use core::{arch::asm, panic::PanicInfo};
 
 use gpio::{gpio_high, gpio_low, set_gpio_state};
+use timer::{delay_nops, sleep};
 
 mod gpio;
+mod timer;
 mod uart;
 
 #[panic_handler]
@@ -31,20 +33,13 @@ extern "C" fn main() {
     }
 
     // Delay so clock speed can stabilize
-    unsafe { delay(50000) }
+    unsafe { delay_nops(50000) }
     uart::print("Hello World!\n");
 
     loop {
         let _ = gpio_high(29);
-        unsafe { delay(1_000_000) }
+        unsafe { sleep(500_000) } // 0.5s
         let _ = gpio_low(29);
-        unsafe { delay(1_000_000) }
+        unsafe { sleep(500_000) } // 0.5s
-    }
-}
-
-unsafe fn delay(count: u32) {
-    for _ in 0..count {
-        // Prevent compiler optimizing away the loop
-        core::arch::asm!("nop");
     }
 }

src/timer.rs

@@ -0,0 +1,18 @@
+const TIMER_CLO: u32 = 0x3F00_3004;
+
+fn read_clo() -> u32 {
+    unsafe { return core::ptr::read_volatile(TIMER_CLO as *const u32) }
+}
+
+pub unsafe fn sleep(microseconds: u32) {
+    let start = read_clo();
+    while read_clo() - start < microseconds {
+        core::arch::asm!("nop");
+    }
+}
+
+pub unsafe fn delay_nops(count: u32) {
+    for _ in 0..count {
+        core::arch::asm!("nop");
+    }
+}

src/uart.rs

@@ -23,6 +23,8 @@ pub fn print(s: &str) {
             core::ptr::write_volatile(UART0_DR as *mut u32, byte as u32);
         }
     }
+    // wait till uart is not busy anymore
+    unsafe { while (core::ptr::read_volatile(UART0_FR as *const u32) >> 3) & 0b1 != 0 {} }
 }
 
 pub fn configure_uart() {