Fix target.mpu-rom-end setting, for ARMv8-M too

targets.json was not specifying the same macro name as the code was
checking for, so setting was ineffective.

Making this work tripped up not-supported checks in ARMv8-M - rather than deal
with making this work, support it instead.

Both ARMv7-M and ARMv8-M slightly reduce code size and runtime impact if
mpu-rom-end is 0x1fffffff, using one fewer region.

This means default setup for ARMv8-M now requires 5 regions, with
mpu-rom-end set to default 0x0fffffff, but this can be put back to 4 by
changing the setting.

Author: kjbracey

hal/mpu/mbed_mpu_v7m.c

@@ -25,7 +25,9 @@
 #error "Device has v7m MPU but it is not enabled. Add 'MPU' to device_has in targets.json"
 #endif
 
-#if !defined(MBED_MPU_ROM_END)
+#ifdef MBED_CONF_TARGET_MPU_ROM_END
+#define MBED_MPU_ROM_END             MBED_CONF_TARGET_MPU_ROM_END
+#else
 #define MBED_MPU_ROM_END             (0x10000000 - 1)
 #endif
 #define MBED_MPU_RAM_START           (MBED_MPU_ROM_END + 1)
@@ -48,9 +50,13 @@ void mbed_mpu_init()
 
     const uint32_t regions = (MPU->TYPE & MPU_TYPE_DREGION_Msk) >> MPU_TYPE_DREGION_Pos;
 
-    // Our MPU setup requires 4 regions - if this assert is hit, remove
-    // DEVICE_MPU from device_has
+    // Our MPU setup requires 3 or 4 regions - if this assert is hit, remove
+    // a region by setting MPU_ROM_END to 0x1fffffff, or remove MPU from device_has
+#if MBED_MPU_RAM_START == 0x20000000
+    MBED_ASSERT(regions >= 3);
+#else
     MBED_ASSERT(regions >= 4);
+#endif
 
     // Disable the MCU
     MPU->CTRL = 0;
@@ -99,11 +105,12 @@ void mbed_mpu_init()
             ARM_MPU_REGION_SIZE_512MB)  // Size
     );
 
-    // Select region 1 and use it for a WT ram region in the Code area
+#if MBED_MPU_RAM_START < 0x20000000
+    // Select region 3 and use it for a WT ram region in the Code area
     // - Code MBED_MPU_ROM_END + 1 to 0x1FFFFFFF
     ARM_MPU_SetRegion(
         ARM_MPU_RBAR(
-            1,                          // Region
+            3,                          // Region
             0x00000000),                // Base
         ARM_MPU_RASR(
             1,                          // DisableExec
@@ -123,13 +130,17 @@ void mbed_mpu_init()
             ((MBED_MPU_RAM_START <= 0x20000000) ? 0 : (1 << 7)),
             ARM_MPU_REGION_SIZE_512MB)  // Size
     );
+#define LAST_RAM_REGION 3
+#else
+#define LAST_RAM_REGION 2
+#endif
 
-    // Select region 2 and use it for WBWA ram regions
+    // Select region 1 and use it for WBWA ram regions
     // - SRAM 0x20000000 to 0x3FFFFFFF
     // - RAM  0x60000000 to 0x7FFFFFFF
     ARM_MPU_SetRegion(
         ARM_MPU_RBAR(
-            2,                          // Region
+            1,                          // Region
             0x00000000),                // Base
         ARM_MPU_RASR(
             1,                          // DisableExec
@@ -150,11 +161,11 @@ void mbed_mpu_init()
             ARM_MPU_REGION_SIZE_4GB)    // Size
     );
 
-    // Select region 3 and use it for the WT ram region
+    // Select region 2 and use it for the WT ram region
     // - RAM 0x80000000 to 0x9FFFFFFF
     ARM_MPU_SetRegion(
         ARM_MPU_RBAR(
-            3,                          // Region
+            2,                          // Region
             0x80000000),                // Base
         ARM_MPU_RASR(
             1,                          // DisableExec
@@ -214,7 +225,7 @@ void mbed_mpu_enable_ram_xn(bool enable)
     // Flush memory writes before configuring the MPU.
     __DMB();
 
-    for (uint32_t region = 1; region <= 3; region++) {
+    for (uint32_t region = 1; region <= LAST_RAM_REGION; region++) {
         enable_region(enable, region);
     }
 

hal/mpu/mbed_mpu_v8m.c

@@ -25,11 +25,15 @@
 #error "Device has v8m MPU but it is not enabled. Add 'MPU' to device_has in targets.json"
 #endif
 
-#if !defined(MBED_MPU_ROM_END)
-#define MBED_MPU_ROM_END             (0x20000000 - 1)
+#ifdef MBED_CONF_TARGET_MPU_ROM_END
+#define MBED_MPU_ROM_END             MBED_CONF_TARGET_MPU_ROM_END
+#else
+#define MBED_MPU_ROM_END             (0x10000000 - 1)
 #endif
+#define MBED_MPU_RAM_START           (MBED_MPU_ROM_END + 1)
 
-MBED_STATIC_ASSERT(MBED_MPU_ROM_END == 0x1fffffff, "Changing MBED_MPU_ROM_END for ARMv8-M is not supported.");
+MBED_STATIC_ASSERT(MBED_MPU_ROM_END <= 0x20000000 - 1,
+                   "Unsupported value for MBED_MPU_ROM_END");
 
 void mbed_mpu_init()
 {
@@ -38,9 +42,13 @@ void mbed_mpu_init()
 
     const uint32_t regions = (MPU->TYPE & MPU_TYPE_DREGION_Msk) >> MPU_TYPE_DREGION_Pos;
 
-    // Our MPU setup requires 4 regions - if this assert is hit, remove
-    // DEVICE_MPU from device_has
+    // Our MPU setup requires 4 or 5 regions - if this assert is hit, remove
+    // a region by setting MPU_ROM_END to 0x1fffffff, or remove MPU from device_has
+#if MBED_MPU_RAM_START == 0x20000000
     MBED_ASSERT(regions >= 4);
+#else
+    MBED_ASSERT(regions >= 5);
+#endif
 
     // Disable the MCU
     MPU->CTRL = 0;
@@ -54,7 +62,7 @@ void mbed_mpu_init()
      * ARMv8-M memory map:
      *
      * Start        End            Name            Executable by default    Default cache       Mbed MPU protection
-     * 0x00000000 - 0x1FFFFFFF     Code            Yes                      WT, WA              Write disabled
+     * 0x00000000 - 0x1FFFFFFF     Code            Yes                      WT, WA              Write disabled for first portion and execute disabled for the rest
      * 0x20000000 - 0x3FFFFFFF     SRAM            Yes                      WB, WA, RA          Execute disabled
      * 0x40000000 - 0x5FFFFFFF     Peripheral      No
      * 0x60000000 - 0x7FFFFFFF     RAM             Yes                      WB, WA, RA          Execute disabled
@@ -82,10 +90,28 @@ void mbed_mpu_init()
             1,                      // Read-Only
             1,                      // Non-Privileged
             0),                     // Execute Never disabled
+        ARM_MPU_RLAR(
+            MBED_MPU_ROM_END,       // Limit
+            AttrIndex_WTRA)         // Attribute index - Write-Through, Read-allocate
+    );
+
+#if MBED_MPU_RAM_START != 0x20000000
+    ARM_MPU_SetRegion(
+        4,                          // Region
+        ARM_MPU_RBAR(
+            MBED_MPU_RAM_START,     // Base
+            ARM_MPU_SH_NON,         // Non-shareable
+            0,                      // Read-Write
+            1,                      // Non-Privileged
+            1),                     // Execute Never enabled
         ARM_MPU_RLAR(
             0x1FFFFFFF,             // Limit
             AttrIndex_WTRA)         // Attribute index - Write-Through, Read-allocate
     );
+#define LAST_RAM_REGION 4
+#else
+#define LAST_RAM_REGION 3
+#endif
 
     ARM_MPU_SetRegion(
         1,                          // Region
@@ -173,7 +199,7 @@ void mbed_mpu_enable_ram_xn(bool enable)
     // Flush memory writes before configuring the MPU.
     __DMB();
 
-    for (uint32_t region = 1; region <= 3; region++) {
+    for (uint32_t region = 1; region <= LAST_RAM_REGION; region++) {
         enable_region(enable, region);
     }
 

targets/targets.json

@@ -32,8 +32,7 @@
             },
             "mpu-rom-end": {
                 "help": "Last address of ROM protected by the MPU",
-                "value": "0x0fffffff",
-                "macro_name": "MPU_ROM_END"
+                "value": "0x0fffffff"
             }
         }
     },