diff --git a/sim/src/api.rs b/sim/src/api.rs
new file mode 100644
index 0000000..71d4643
--- /dev/null
+++ b/sim/src/api.rs
@@ -0,0 +1,34 @@
+//! HAL api for MyNewt applications
+
+use flash::{Result, Flash};
+use libc;
+use std::slice;
+
+// This isn't meant to call directly, but by a wrapper.
+
+#[no_mangle]
+pub extern fn sim_flash_erase(dev: *mut Flash, offset: u32, size: u32) -> libc::c_int {
+    let mut dev: &mut Flash = unsafe { &mut *dev };
+    map_err(dev.erase(offset as usize, size as usize))
+}
+
+#[no_mangle]
+pub extern fn sim_flash_read(dev: *const Flash, offset: u32, dest: *mut u8, size: u32) -> libc::c_int {
+    let dev: &Flash = unsafe { &*dev };
+    let mut buf: &mut[u8] = unsafe { slice::from_raw_parts_mut(dest, size as usize) };
+    map_err(dev.read(offset as usize, &mut buf))
+}
+
+#[no_mangle]
+pub extern fn sim_flash_write(dev: *mut Flash, offset: u32, src: *const u8, size: u32) -> libc::c_int {
+    let mut dev: &mut Flash = unsafe { &mut *dev };
+    let buf: &[u8] = unsafe { slice::from_raw_parts(src, size as usize) };
+    map_err(dev.write(offset as usize, &buf))
+}
+
+fn map_err(err: Result<()>) -> libc::c_int {
+    match err {
+        Ok(()) => 0,
+        Err(_) => -1,
+    }
+}