Clear caches before RAM execution in MPU test

Ensure that code written to ram is flushed and that caches are cleared
before attempting to executing from ram. This fixes CI failures on the
MPU test when it is built for Cotex-M7 devices such as the
NUCLEO-F746ZG.

TESTS/mbed_hal/mpu/main.cpp

@@ -41,6 +41,21 @@ uint32_t real_hard_fault_handler;
 static volatile uint16_t data_function = ASM_BX_LR;
 static volatile uint16_t bss_function;
 
+static void clear_caches()
+{
+#if defined(__CORTEX_M7)
+        /* Data cache clean and invalid */
+        SCB_CleanInvalidateDCache();
+
+        /* Instruction cache invalid */
+        SCB_InvalidateICache();
+#endif
+
+    __ISB();
+    __DSB();
+
+}
+
 static void call_mem(const volatile uint16_t *mem_function)
 {
     // or the address with 1 to ensure the thumb bit is set
@@ -112,6 +127,7 @@ void mpu_fault_test_data()
 void mpu_fault_test_bss()
 {
     bss_function = ASM_BX_LR;
+    clear_caches();
     mpu_fault_test(&bss_function);
 }
 
@@ -120,6 +136,7 @@ void mpu_fault_test_stack()
     uint16_t stack_function;
 
     stack_function = ASM_BX_LR;
+    clear_caches();
     mpu_fault_test(&stack_function);
 }
 
@@ -129,6 +146,7 @@ void mpu_fault_test_heap()
 
     TEST_ASSERT_NOT_EQUAL(NULL, heap_function);
     *heap_function = ASM_BX_LR;
+    clear_caches();
     mpu_fault_test(heap_function);
 
     free(heap_function);