sam3x8e: Add initial support for Arduino Due boards

This adds basic support for running on the Atmel SAM3x8e
micro-controllers that are found in the Arudino Due boards.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/sam3x8e/irq.h

@@ -0,0 +1,26 @@
+#ifndef __SAM3X8E_IRQ_H
+#define __SAM3X8E_IRQ_H
+// Definitions for irq enable/disable on ARM Cortex-M
+
+static inline void irq_disable(void) {
+    asm volatile("cpsid i" ::: "memory");
+}
+
+static inline void irq_enable(void) {
+    asm volatile("cpsie i" ::: "memory");
+}
+
+typedef unsigned long irqstatus_t;
+
+static inline irqstatus_t irq_save(void) {
+    irqstatus_t flag;
+    asm volatile("mrs %0, primask" : "=r" (flag) :: "memory");
+    irq_disable();
+    return flag;
+}
+
+static inline void irq_restore(irqstatus_t flag) {
+    asm volatile("msr primask, %0" :: "r" (flag) : "memory");
+}
+
+#endif // irq.h