2 files changed, 38 insertions, 0 deletions

diff --git a/src/add_one.c b/src/add_one.c
new file mode 100644
index 0000000..74853d0
--- /dev/null
+++ b/src/add_one.c
@@ -0,0 +1 @@
+int c_add_one(int x) { return x + 1; }
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..3781a12
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,37 @@
+#![no_main]
+#![no_std]
+
+use core::{fmt::Write, ffi::c_int};
+use cortex_m_rt::entry;
+use microbit::{
+    hal::uart::{Uart, Baudrate, Parity},
+    Board,
+};
+
+extern crate panic_halt;
+extern crate microbit;
+extern "C" {
+     fn c_add_one(x: c_int) -> c_int;
+}
+
+pub fn add_one(x: i32) -> i32 {
+    unsafe {
+        c_add_one(x)
+    }
+}
+
+#[entry]
+fn main() -> ! {
+    let board = Board::take().unwrap();
+    let mut serial = Uart::new(
+        board.UART0,
+        board.uart.into(),
+        Parity::EXCLUDED,
+        Baudrate::BAUD115200,
+    );
+
+    let ten_plus_one = add_one(10);
+    writeln!(serial, "10 + 1 = {}\r", ten_plus_one).unwrap();
+
+    loop {}
+}