Updated with code from http://playground.arduino.cc/code/AvailableMemory

.gitignore

@@ -1,3 +1,9 @@
 *.o
 *.orig
 .*.swp
+[._]*.s[a-w][a-z]
+[._]s[a-w][a-z]
+*.un~
+Session.vim
+.netrwhist
+*~

.travis.yml

@@ -0,0 +1,31 @@
+language: c
+sudo: false
+before_install:
+  - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_1.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :1 -ac -screen 0 1280x1024x16"
+  - sleep 3
+  - export DISPLAY=:1.0
+  - wget http://downloads.arduino.cc/arduino-1.6.9-linux64.tar.xz
+  - tar xf arduino-1.6.9-linux64.tar.xz
+  - mv arduino-1.6.9 $HOME/arduino_ide
+install:
+  - ln -s $PWD $HOME/arduino_ide/libraries/MemoryFree
+  - export PATH="$HOME/arduino_ide:$PATH"
+  - arduino --pref "boardsmanager.additional.urls=https://adafruit.github.io/arduino-board-index/package_adafruit_index.json,http://arduino.esp8266.com/stable/package_esp8266com_index.json" --save-prefs 2>&1
+  - arduino --install-boards arduino:sam 2>&1 /dev/null
+  - arduino --install-boards arduino:samd 2>&1 /dev/null
+  - arduino --install-boards esp8266:esp8266 2>&1 /dev/null
+  - arduino --install-boards adafruit:avr 2>&1 /dev/null
+  - arduino --install-library TinyWireM 2>&1
+  - arduino --pref "compiler.warning_level=all" --save-prefs
+script:
+  - arduino --verify --board arduino:avr:uno $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board arduino:sam:arduino_due_x $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board arduino:samd:zero $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board esp8266:esp8266:huzzah $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board arduino:avr:leonardo $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board adafruit:avr:trinket5 $PWD/examples/FreeMemory/FreeMemory.ino
+  - arduino --verify --board arduino:avr:gemma $PWD/examples/FreeMemory/FreeMemory.ino
+notifications:
+  email:
+    on_success: change
+    on_failure: change

MemoryFree.cpp

@@ -1,18 +1,52 @@
-extern unsigned int __bss_end;
+#if (ARDUINO >= 100)
+#include <Arduino.h>
+#else
+#include <WProgram.h>
+#endif
+
 extern unsigned int __heap_start;
 extern void *__brkval;
 
+/*
+ * The free list structure as maintained by the
+ * avr-libc memory allocation routines.
+ */
+struct __freelist
+{
+  size_t sz;
+  struct __freelist *nx;
+};
+
+/* The head of the free list structure */
+extern struct __freelist *__flp;
 
 #include "MemoryFree.h"
 
+/* Calculates the size of the free list */
+int freeListSize()
+{
+  struct __freelist* current;
+  int total = 0;
+  for (current = __flp; current; current = current->nx)
+  {
+    total += 2; /* Add two bytes for the memory block's header  */
+    total += (int) current->sz;
+  }
 
-int freeMemory() {
-  int free_memory;
+  return total;
+}
 
-  if((int)__brkval == 0)
-     free_memory = ((int)&free_memory) - ((int)&__bss_end);
+int freeMemory()
+{
+  int free_memory;
+  if ((int)__brkval == 0)
+  {
+    free_memory = ((int)&free_memory) - ((int)&__heap_start);
+  }
   else
+  {
     free_memory = ((int)&free_memory) - ((int)__brkval);
-
+    free_memory += freeListSize();
+  }
   return free_memory;
 }

MemoryFree.h

@@ -1,3 +1,7 @@
+// MemoryFree library based on code posted here:
+// http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1213583720/15
+// Extended by Matthew Murdoch to include walking of the free list.
+
 #ifndef	MEMORY_FREE_H
 #define MEMORY_FREE_H
 
@@ -12,4 +16,3 @@ int freeMemory();
 #endif
 
 #endif
-

README → README.md

@@ -1,3 +1,5 @@
 This is the excellent MemoryFree library from http://www.arduino.cc/playground/Code/AvailableMemory.
 
 I am hosting it here so there is a quick and easy way to pull it down.
+
+(20 Mar 2015) Repository updated with code from http://playground.arduino.cc/code/AvailableMemory

examples/FreeMemory/FreeMemory.ino

@@ -0,0 +1,31 @@
+#include <MemoryFree.h>
+
+// On Arduino Leonardo with ATmega32U4:
+//
+// Reported free memory with str commented out:
+// 2373 bytes
+//
+// Reported free memory with str and Serial.println(str) uncommented:
+// 2359 bytes
+//
+// Difference: 14 bytes (13 ASCII chars + null terminator)
+
+// 14-bytes string
+//char str[] = "Hello, world!";
+
+void setup() {
+  //Initialize serial and wait for port to open:
+  Serial.begin(115200);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for Leonardo only
+  }
+}
+
+void loop() {
+//  Serial.println(str);
+
+  Serial.print("freeMemory()=");
+  Serial.println(freeMemory());
+
+  delay(1000);
+}