examples: Add support for a simple CTAP example

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

examples/ctap.rs

diff --git a/examples/ctap.rs b/examples/ctap.rs
new file mode 100644
index 0000000..42917d1
--- /dev/null
+++ b/examples/ctap.rs
@@ -0,0 +1,46 @@
+#![no_std]
+/// This is a very basic CTAP example
+/// This example only calls the CTAP driver calls, it does not implement CTAP
+use core::fmt::Write;
+use libtock::ctap::{CtapRecvBuffer, CtapSendBuffer};
+use libtock::result::TockResult;
+use libtock::syscalls;
+
+#[libtock::main]
+async fn main() -> TockResult<()> {
+    let mut drivers = libtock::retrieve_drivers()?;
+    let mut console = drivers.console.create_console();
+    writeln!(console, "Starting CTAP example")?;
+    let ctap_driver = drivers.ctap.init_driver()?;
+
+    writeln!(console, "Creating recv buffer")?;
+    let mut recv_buffer = CtapRecvBuffer::default();
+    let recv_buffer = ctap_driver.init_recv_buffer(&mut recv_buffer)?;
+    writeln!(console, "  done")?;
+
+    writeln!(console, "Creating send buffer")?;
+    let mut send_buffer = CtapSendBuffer::default();
+    let _send_buffer = ctap_driver.init_send_buffer(&mut send_buffer)?;
+    writeln!(console, "  done")?;
+
+    let mut temp_buffer = [0; libtock::ctap::RECV_BUFFER_SIZE];
+
+    writeln!(console, "Setting callback and running")?;
+    let mut callback = |_, _| {
+        writeln!(console, "CTAP Complete, printing data").unwrap();
+        recv_buffer.read_bytes(&mut temp_buffer[..]);
+
+        for buf in temp_buffer.iter().take(libtock::ctap::RECV_BUFFER_SIZE) {
+            write!(console, "{:x}", *buf).unwrap();
+        }
+
+        let _ret = ctap_driver.allow_receive();
+    };
+
+    let _subscription = ctap_driver.subscribe(&mut callback)?;
+    ctap_driver.allow_receive()?;
+
+    loop {
+        unsafe { syscalls::raw::yieldk() };
+    }
+}