diff --git a/sim/mcuboot-sys/src/api.rs b/sim/mcuboot-sys/src/api.rs
new file mode 100644
index 0000000..4e744e2
--- /dev/null
+++ b/sim/mcuboot-sys/src/api.rs
@@ -0,0 +1,85 @@
+//! HAL api for MyNewt applications
+
+use simflash::{Result, Flash};
+use libc;
+use log::LogLevel;
+use std::mem;
+use std::slice;
+
+// The current active flash device.  The 'static is a lie, and we manage the lifetime ourselves.
+static mut FLASH: Option<*mut Flash> = None;
+
+// Set the flash device to be used by the simulation.  The pointer is unsafely stashed away.
+pub unsafe fn set_flash(dev: &mut Flash) {
+    let dev: &'static mut Flash = mem::transmute(dev);
+    FLASH = Some(dev as *mut Flash);
+}
+
+pub unsafe fn clear_flash() {
+    FLASH = None;
+}
+
+// Retrieve the flash, returning an error from the enclosing function.  We can't panic here because
+// we've called through C and unwinding is prohibited (it seems to just exit the program).
+macro_rules! get_flash {
+    () => {
+        match FLASH {
+            Some(x) => &mut *x,
+            None => return -19,
+        }
+    }
+}
+
+// This isn't meant to call directly, but by a wrapper.
+
+#[no_mangle]
+pub extern fn sim_flash_erase(offset: u32, size: u32) -> libc::c_int {
+    let dev = unsafe { get_flash!() };
+    map_err(dev.erase(offset as usize, size as usize))
+}
+
+#[no_mangle]
+pub extern fn sim_flash_read(offset: u32, dest: *mut u8, size: u32) -> libc::c_int {
+    let dev = unsafe { get_flash!() };
+    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(offset: u32, src: *const u8, size: u32) -> libc::c_int {
+    let dev = unsafe { get_flash!() };
+    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(e) => {
+            warn!("{}", e);
+            -1
+        },
+    }
+}
+
+/// Called by C code to determine if we should log at this level.  Levels are defined in
+/// bootutil/bootutil_log.h.  This makes the logging from the C code controlled by bootsim::api, so
+/// for example, it can be enabled with something like:
+///     RUST_LOG=bootsim::api=info cargo run --release runall
+/// or
+///     RUST_LOG=bootsim=info cargo run --release runall
+#[no_mangle]
+pub extern fn sim_log_enabled(level: libc::c_int) -> libc::c_int {
+    let res = match level {
+        1 => log_enabled!(LogLevel::Error),
+        2 => log_enabled!(LogLevel::Warn),
+        3 => log_enabled!(LogLevel::Info),
+        4 => log_enabled!(LogLevel::Trace),
+        _ => false,
+    };
+    if res {
+        1
+    } else {
+        0
+    }
+}