Make malloc return NULL when SAMD boards run out of RAM

cores/arduino/main.cpp

@@ -59,3 +59,10 @@ int main( void )
 
   return 0;
 }
+
+// Ensure our version of sbrk is used by forcing a reference to it here
+// (without this, an undefined reference only occurs later when linking
+// newlib, and the dummy from libgloss/nosys will be used instead).
+// This variable will be optimized away later.
+extern "C" void *_sbrk(int);
+void * force_reference_to_sbrk = (void*)&_sbrk;

cores/arduino/sbrk.c

@@ -0,0 +1,39 @@
+/*
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include <sam.h>
+#include <stddef.h>
+#include <errno.h>
+
+/* How much free space to keep between the stack and the heap by malloc.
+ * Can be changed by the application at any time. */
+size_t __malloc_margin = 64;
+
+void *_sbrk(int incr)
+{
+  extern char end; /* End of global variables, defined by the linker */
+  static char *brkval = &end ;
+  char *prev_brkval = brkval;
+
+  if (incr > 0 && brkval + incr + __malloc_margin > (char *)__get_MSP()) {
+    /* Heap and stack collision */
+    errno = ENOMEM;
+    return (void*) -1;
+  }
+
+  brkval += incr ;
+  return (void*) prev_brkval;
+}