bsps/atsam: Add NULL pointer protection

spec/build/bsps/arm/atsam/bspatsam.yml

@@ -296,6 +296,8 @@ links:
   uid: optmck
 - role: build-dependency
   uid: optnocachesz
+- role: build-dependency
+  uid: optnullsz
 - role: build-dependency
   uid: optoscmain
 - role: build-dependency

spec/build/bsps/arm/atsam/linkcmds.yml

@@ -2,7 +2,8 @@ SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
 build-type: config-file
 content: |
   MEMORY {
-    ITCM      : ORIGIN = 0x00000000, LENGTH = ${ATSAM_MEMORY_TCM_SIZE}
+    NULL      : ORIGIN = 0x00000000, LENGTH = ${ATSAM_MEMORY_NULL_SIZE}
+    ITCM      : ORIGIN = ${ATSAM_MEMORY_NULL_SIZE}, LENGTH = ((${ATSAM_MEMORY_TCM_SIZE} > ${ATSAM_MEMORY_NULL_SIZE}) ? (${ATSAM_MEMORY_TCM_SIZE} - ${ATSAM_MEMORY_NULL_SIZE}) : 0)
     INTFLASH  : ORIGIN = 0x00400000, LENGTH = ${ATSAM_MEMORY_INTFLASH_SIZE}
     DTCM      : ORIGIN = 0x20000000, LENGTH = ${ATSAM_MEMORY_TCM_SIZE}
     INTSRAM   : ORIGIN = 0x20400000, LENGTH = ${ATSAM_MEMORY_INTSRAM_SIZE} - 2 * ${ATSAM_MEMORY_TCM_SIZE} - ${ATSAM_MEMORY_NOCACHE_SIZE}
@@ -13,6 +14,10 @@ content: |
 
   /* Must be used only for MPU definitions */
 
+  atsam_memory_null_begin = ORIGIN (NULL);
+  atsam_memory_null_end = ORIGIN (NULL) + LENGTH (NULL);
+  atsam_memory_null_size = LENGTH (NULL);
+
   atsam_memory_itcm_begin = ORIGIN (ITCM);
   atsam_memory_itcm_end = ORIGIN (ITCM) + LENGTH (ITCM);
   atsam_memory_itcm_size = LENGTH (ITCM);

spec/build/bsps/arm/atsam/optnullsz.yml

@@ -0,0 +1,17 @@
+SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
+actions:
+- get-integer: null
+- env-assign: null
+build-type: option
+default: 0
+default-by-variant: []
+enabled-by: true
+format: '{:#010x}'
+links: []
+name: ATSAM_MEMORY_NULL_SIZE
+description: |
+  Size of the NULL pointer protection area in bytes.  This memory area reduces
+  the size of the ITCM available to the application.
+type: build
+copyrights:
+- Copyright (C) 2020 embedded brains GmbH (http://www.embedded-brains.de)

spec/build/bsps/arm/atsam/opttcmsz.yml

@@ -9,7 +9,8 @@ copyrights:
 default: 0
 default-by-variant: []
 description: |
-  size of tightly coupled memories (TCM) in bytes
+  Size of tightly coupled memories (TCM) in bytes.  Note that the ITCM is
+  reduced by the ATSAM_MEMORY_NULL_SIZE option.  DTCM is unaffected.
 enabled-by: true
 format: '{:#010x}'
 links: []