Integrate MPU with mbed

Enable the MPU as part of the boot sequence and disable it before
starting a new application. Also add reference counted MPU lock and
unlock functions to allow code to execute from ram when necessary.

platform/mbed_application.c

@@ -18,6 +18,7 @@
 #include <stdarg.h>
 #include "device.h"
 #include "platform/mbed_application.h"
+#include "hal/mpu_api.h"
 
 #if MBED_APPLICATION_SUPPORT
 
@@ -67,6 +68,7 @@ void mbed_start_application(uintptr_t address)
     SysTick->CTRL = 0x00000000;
     powerdown_nvic();
     powerdown_scb(address);
+    mbed_mpu_free();
 
     sp = *((void **)address + 0);
     pc = *((void **)address + 1);

platform/mbed_mpu_mgmt.c

@@ -0,0 +1,51 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2018 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "platform/mbed_mpu_mgmt.h"
+#include "platform/mbed_critical.h"
+#include "platform/mbed_error.h"
+#include "hal/mpu_api.h"
+#include <limits.h>
+
+static uint16_t mem_xn_lock;
+
+void mbed_mpu_manager_lock_mem_xn()
+{
+    core_util_critical_section_enter();
+    if (mem_xn_lock == USHRT_MAX) {
+        core_util_critical_section_exit();
+        MBED_ERROR1(MBED_MAKE_ERROR(MBED_MODULE_PLATFORM, MBED_ERROR_CODE_OVERFLOW), "Memory execute never lock overflow (> USHRT_MAX)", mem_xn_lock);
+    }
+    if (mem_xn_lock == 0) {
+        mbed_mpu_enable_ram_xn(false);
+    }
+    mem_xn_lock++;
+    core_util_critical_section_exit();
+}
+
+void mbed_mpu_manager_unlock_mem_xn()
+{
+    core_util_critical_section_enter();
+    if (mem_xn_lock == 0) {
+        core_util_critical_section_exit();
+        MBED_ERROR1(MBED_MAKE_ERROR(MBED_MODULE_PLATFORM, MBED_ERROR_CODE_UNDERFLOW), "Memory execute never lock underflow (< 0)", mem_xn_lock);
+    }
+    mem_xn_lock--;
+    if (mem_xn_lock == 0) {
+        mbed_mpu_enable_ram_xn(true);
+    }
+    core_util_critical_section_exit();
+}

platform/mbed_mpu_mgmt.h

@@ -0,0 +1,66 @@
+/** \addtogroup platform */
+/** @{*/
+/**
+ * \defgroup platform_mpu_mgmt MPU management functions
+ * @{
+ */
+
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2018 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef MBED_MPU_MGMT_H
+#define MBED_MPU_MGMT_H
+
+#include "hal/sleep_api.h"
+#include "mbed_toolchain.h"
+#include "hal/ticker_api.h"
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Lock ram execute never mode off
+ *
+ * This disables the MPU's execute never ram protection and allows
+ * functions to run from RAM. Execution directly from ram will be
+ * allowed if this function is invoked at least once(the internal
+ * counter is non-zero).
+ *
+ * Use this locking mechanism for code which needs to execute from
+ * ram such as flash programming algorithms and ram thunks.
+ *
+ * The lock is a counter, can be locked up to USHRT_MAX
+ * This function is IRQ and thread safe
+ */
+void mbed_mpu_manager_lock_mem_xn(void);
+
+/** Unlock ram execute never mode
+ *
+ * Use unlocking in pair with mbed_mpu_manager_lock_mem_xn().
+ *
+ * The lock is a counter, should be equally unlocked as locked
+ * This function is IRQ and thread safe
+ */
+void mbed_mpu_manager_unlock_mem_xn(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
+/** @}*/
+/** @}*/

rtos/TARGET_CORTEX/mbed_boot.c

@@ -76,6 +76,7 @@
 #include "mbed_toolchain.h"
 #include "mbed_boot.h"
 #include "mbed_error.h"
+#include "mpu_api.h"
 
 int main(void);
 static void mbed_cpy_nvic(void);
@@ -86,6 +87,8 @@ uint32_t mbed_stack_isr_size = 0;
 
 void mbed_init(void)
 {
+    mbed_mpu_init();
+    mbed_mpu_enable_ram_xn(true);
     mbed_cpy_nvic();
     mbed_sdk_init();
     mbed_rtos_init();