arm: async echo app

arm/lock.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "aum1_cm1.h"
+
+struct InterruptLock {
+    bool was_locked;
+
+    InterruptLock()
+        : was_locked(__get_PRIMASK() != 0) {
+            __disable_irq();
+        }
+
+    ~InterruptLock() {
+        if (!was_locked) {
+            __enable_irq();
+        }
+    }
+};