Import https://github.com/tock/libtock-rs at commit 828c19d into third_party/libtock-drivers/.

third_party/libtock-drivers/src/rng.rs

@@ -0,0 +1,42 @@
+use crate::callback::Identity0Consumer;
+use crate::futures;
+use crate::result::TockResult;
+use crate::syscalls;
+use core::cell::Cell;
+use core::mem;
+
+const DRIVER_NUMBER: usize = 0x40001;
+
+mod command_nr {
+    pub const REQUEST_RNG: usize = 1;
+}
+
+mod subscribe_nr {
+    pub const BUFFER_FILLED: usize = 0;
+}
+
+mod allow_nr {
+    pub const SHARE_BUFFER: usize = 0;
+}
+
+#[non_exhaustive]
+pub struct RngDriver;
+
+impl RngDriver {
+    pub async fn fill_buffer(&mut self, buf: &mut [u8]) -> TockResult<()> {
+        let buf_len = buf.len();
+        let shared_memory = syscalls::allow(DRIVER_NUMBER, allow_nr::SHARE_BUFFER, buf)?;
+        let is_filled = Cell::new(false);
+        let mut is_filled_alarm = || is_filled.set(true);
+        let subscription = syscalls::subscribe::<Identity0Consumer, _>(
+            DRIVER_NUMBER,
+            subscribe_nr::BUFFER_FILLED,
+            &mut is_filled_alarm,
+        )?;
+        syscalls::command(DRIVER_NUMBER, command_nr::REQUEST_RNG, buf_len, 0)?;
+        futures::wait_until(|| is_filled.get()).await;
+        mem::drop(subscription);
+        mem::drop(shared_memory);
+        Ok(())
+    }
+}