rust: Add simple debug macros

Add simple debug!() and debugln!() macros that can be used for everywhere
to print stuff to UARTHS.

rust/k210-shared/src/debug.rs

@@ -0,0 +1,40 @@
+/** Simple logging functionality that prints to UARTHS at the current settings.
+ * The advantage of this is that it can be used from anywhere without having to pass
+ * stdout around. The disadvantage is that this prevents rust's safety rules from preventing
+ * concurrent access. It also assumes someone else set up the UART already.
+ */
+use k210_hal::pac;
+pub use core::fmt::Write;
+
+pub struct DebugLogger;
+
+impl Write for DebugLogger {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        let uart = unsafe {&*pac::UARTHS::ptr() };
+        for &byte in s.as_bytes() {
+            while uart.txdata.read().full().bit_is_set() {
+                continue;
+            }
+            unsafe {
+                uart.txdata.write(|w| w.data().bits(byte));
+            }
+        }
+        Ok(())
+    }
+}
+
+#[macro_export]
+macro_rules! debugln {
+    ($($arg:tt)+) => ({
+        let mut stdout = $crate::debug::DebugLogger {};
+        writeln!(stdout, $($arg)+).unwrap();
+    })
+}
+
+#[macro_export]
+macro_rules! debug {
+    ($($arg:tt)+) => ({
+        let mut stdout = $crate::debug::DebugLogger {};
+        write!(stdout, $($arg)+).unwrap();
+    })
+}

rust/k210-shared/src/lib.rs

@@ -5,6 +5,7 @@
 
 pub mod board;
 #[cfg(not(test))]
+pub mod debug;
 pub mod panic;
 pub mod soc;
 pub mod timing;