Fix UART output

.vscode/tasks.json

@@ -14,7 +14,7 @@
     {
       "label": "Run QEMU",
       "type": "shell",
-      "command": "qemu-system-aarch64 -M raspi3b -cpu cortex-a72 -display none -kernel ${workspaceFolder}/target/aarch64-unknown-none/debug/nova -s -S",
+      "command": "qemu-system-aarch64 -M raspi3b -cpu cortex-a53 -display none -kernel ${workspaceFolder}/target/aarch64-unknown-none/debug/nova -s -S -serial stdio",
       "isBackground": true
     }
   ]

src/main.rs

@@ -13,15 +13,33 @@ fn panic(_panic: &PanicInfo) -> ! {
     loop {}
 }
 
+const BAUD: u32 = 115200;
+const UART_CLK: u32 = 48_000_000;
+
 const UART0_DR: u32 = 0x3F20_1000;
 
+const UART0_FR: u32 = 0x3F20_1018;
+const UART0_FR_TXFF: u32 = 1 << 5;
+
+const UART0_IBRD: u32 = 0x3F20_1024;
+const UART0_FBRD: u32 = 0x3F20_1028;
+
+const UART0_CR: u32 = 0x3F20_1030;
+const UART0_CR_UARTEN: u32 = 1 << 0;
+const UART0_CR_TXE: u32 = 1 << 8;
+
+const UART0_LCRH: u32 = 0x3F20_102c;
+const UART0_LCRH_FEN: u32 = 1 << 4;
+const UART0_LCRH_WLEN: u32 = 11 << 5;
+
 struct Uart;
 
 impl Write for Uart {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         for byte in s.bytes() {
             unsafe {
-                core::ptr::write_volatile(UART0_DR as *mut u8, byte);
+                while core::ptr::read_volatile(UART0_FR as *const u32) & UART0_FR_TXFF != 0 {}
+                core::ptr::write_volatile(UART0_DR as *mut u32, byte as u32);
             }
         }
         Ok(())
@@ -36,7 +54,77 @@ pub extern "C" fn _start() -> ! {
 
 #[no_mangle]
 fn main() {
+    configure_uart();
+    delay(50000);
     let mut uart = Uart {};
-    writeln!(uart, "Hello World!\n");
-    loop {}
+    loop {
+        writeln!(uart, "Hello World!");
+    }
+}
+
+pub fn configure_uart() {
+    let baud_div_times_64 = (UART_CLK * 4) / BAUD;
+
+    let ibrd = baud_div_times_64 / 64;
+    let fbrd = baud_div_times_64 % 64;
+
+    unsafe {
+        uart_enable(false);
+        uart_fifo_enable(false);
+
+        core::ptr::write_volatile(UART0_IBRD as *mut u32, ibrd);
+        core::ptr::write_volatile(UART0_FBRD as *mut u32, fbrd);
+
+        uart_set_lcrh(0b11, true);
+
+        // Enable transmit and uart
+        let mut cr = core::ptr::read_volatile(UART0_CR as *mut u32);
+        cr |= UART0_CR_UARTEN | UART0_CR_TXE;
+        core::ptr::write_volatile(UART0_CR as *mut u32, cr);
+    }
+}
+
+fn uart_enable(enable: bool) {
+    unsafe {
+        let mut cr = core::ptr::read_volatile(UART0_CR as *mut u32);
+
+        if enable {
+            cr |= UART0_CR_UARTEN;
+        } else {
+            cr &= !UART0_CR_UARTEN;
+        }
+
+        core::ptr::write_volatile(UART0_CR as *mut u32, cr);
+    }
+}
+
+fn uart_fifo_enable(enable: bool) {
+    unsafe {
+        let mut lcrh = core::ptr::read_volatile(UART0_LCRH as *mut u32);
+
+        if enable {
+            lcrh |= UART0_LCRH_FEN;
+        } else {
+            lcrh &= !UART0_LCRH_FEN;
+        }
+
+        core::ptr::write_volatile(UART0_LCRH as *mut u32, lcrh);
+    }
+}
+
+fn uart_set_lcrh(wlen: u32, enable_fifo: bool) {
+    unsafe {
+        let mut value = (wlen & 0b11) << 5;
+        if enable_fifo {
+            value |= UART0_LCRH_FEN;
+        }
+        core::ptr::write_volatile(UART0_LCRH as *mut u32, value);
+    }
+}
+
+fn delay(count: u32) {
+    for _ in 0..count {
+        // Prevent compiler optimizing away the loop
+        core::sync::atomic::spin_loop_hint();
+    }
 }