Sample of how to generate the function

app/lpc55xpresso/Cargo.toml

@@ -18,6 +18,8 @@ abi = { path = "../../sys/abi"}
 kern = { path = "../../sys/kern" }
 lpc55-rot-startup = {path = "../../lib/lpc55-rot-startup"}
 unwrap-lite = {path = "../../lib/unwrap-lite"}
+lpc55_romapi = { path = "../../lib/lpc55-romapi" }
+lpc55-hashcrypt = { path = "../../lib/lpc55-hashcrypt" }
 
 # this lets you use `cargo fix`!
 [[bin]]

app/lpc55xpresso/src/main.rs

@@ -16,7 +16,13 @@ fn main() -> ! {
 
     let (cycles_per_ms, _div) = get_clock_speed(&peripherals);
 
+    set_hashcrypt_rom();
+
     startup(&core_peripherals, &peripherals);
 
+    set_hashcrypt_default();
+
     unsafe { kern::startup::start_kernel(cycles_per_ms * 1_000) }
 }
+
+lpc55_hashcrypt::dynamic_hashcrypt!();

lib/lpc55-hashcrypt/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "lpc55-hashcrypt"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+cfg-if = { workspace = true }
+proc-macro2 = { workspace = true }
+quote = { workspace = true }
+zerocopy = { workspace = true }
+syn = { workspace = true }
+
+[build-dependencies]
+build-util = { path = "../../build/util" }
+
+[lib]
+proc-macro = true

lib/lpc55-hashcrypt/src/lib.rs

@@ -0,0 +1,42 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+/// proc macro to generate iocon function for LPC55
+extern crate proc_macro;
+use proc_macro::TokenStream;
+extern crate proc_macro2;
+use quote::quote;
+
+#[proc_macro]
+pub fn dynamic_hashcrypt(_item: TokenStream) -> TokenStream {
+    let code = quote! {
+        static mut USE_ROM: core::sync::atomic::AtomicBool = core::sync::atomic::AtomicBool::new(false);
+
+        pub fn set_hashcrypt_default() {
+            unsafe {
+                USE_ROM.store(false, core::sync::atomic::Ordering::Relaxed);
+            }
+        }
+
+        pub fn set_hashcrypt_rom() {
+            unsafe {
+                USE_ROM.store(true, core::sync::atomic::Ordering::Relaxed);
+            }
+        }
+
+        #[allow(non_snake_case)]
+        #[no_mangle]
+        pub unsafe extern "C" fn HASHCRYPT() {
+            if USE_ROM.load(core::sync::atomic::Ordering::Relaxed) {
+                lpc55_romapi::skboot_hashcrypt_handler();
+            } else {
+                kern::arch::DefaultHandler();
+            }
+
+        }
+
+    };
+
+    code.into()
+}

lib/lpc55-rot-startup/Cargo.toml

@@ -31,6 +31,7 @@ lpc55_romapi = { path = "../lpc55-romapi" }
 stage0-handoff = { path = "../stage0-handoff"}
 unwrap-lite = { path = "../unwrap-lite" }
 drv-lpc55-flash.path = "../../drv/lpc55-flash"
+lpc55-hashcrypt = { path = "../lpc55-hashcrypt" }
 
 [build-dependencies]
 build-util = { path = "../../build/util" }