Merge pull request #133 from DCC-EX/neil-updates

Protect minimum memory threshold against interrupts.

CommandStation-EX.ino

@@ -123,15 +123,13 @@ void loop()
 
   LCDDisplay::loop();  // ignored if LCD not in use 
   
-// Optionally report any decrease in memory (will automatically trigger on first call)
+  // Report any decrease in memory (will automatically trigger on first call)
-#if ENABLE_FREE_MEM_WARNING
+  static int ramLowWatermark = __INT_MAX__; // replaced on first loop 
-  static int ramLowWatermark = 32767; // replaced on first loop 
 
-  int freeNow = updateMinimumFreeMemory();
+  int freeNow = minimumFreeMemory();
   if (freeNow < ramLowWatermark)
   {
     ramLowWatermark = freeNow;
     LCD(2,F("Free RAM=%5db"), ramLowWatermark);
   }
-#endif
 }

DCCEXParser.cpp

@@ -720,7 +720,7 @@ bool DCCEXParser::parseD(Print *stream, int params, int p[])
         return true;
 
     case HASH_KEYWORD_RAM: // <D RAM>
-        StringFormatter::send(stream, F("\nFree memory=%d\n"), freeMemory());
+        StringFormatter::send(stream, F("\nFree memory=%d\n"), minimumFreeMemory());
         break;
 
     case HASH_KEYWORD_ACK: // <D ACK ON/OFF> <D ACK [LIMIT|MIN|MAX] Value>

config.example.h

@@ -111,6 +111,4 @@ The configuration file for DCC-EX Command Station
 // #define OLED_DRIVER 128,32
 
 /////////////////////////////////////////////////////////////////////////////////////
-//
+
-// Enable warning as memory gets depleted
-#define ENABLE_FREE_MEM_WARNING false

freeMemory.cpp

@@ -18,6 +18,7 @@
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <Arduino.h>
 #include "freeMemory.h"
 
 // thanks go to  https://github.com/mpflaga/Arduino-MemoryFree
@@ -31,25 +32,40 @@ extern char *__malloc_heap_start;
 #endif
 
 
-static volatile int minimum_free_memory = 32767;
+static volatile int minimum_free_memory = __INT_MAX__;
 
 
-int freeMemory() {
+static inline int freeMemory() {
   char top;
 #if defined(__arm__)
   return &top - reinterpret_cast<char*>(sbrk(0));
 #elif defined(__AVR__)
   return __brkval ? &top - __brkval : &top - __malloc_heap_start;
 #else
-#error bailed out alredy above
+#error bailed out already above
 #endif
 }
 
 // Update low ram level.  Allow for extra bytes to be specified
 // by estimation or inspection, that may be used by other 
-// called subroutines.
+// called subroutines.  Must be called with interrupts disabled.
-int updateMinimumFreeMemory(unsigned char extraBytes) {
+// 
+// Although __brkval may go up and down as heap memory is allocated
+// and freed, this function records only the worst case encountered.
+// So even if all of the heap is freed, the reported minimum free 
+// memory will not increase.
+//
+void updateMinimumFreeMemory(unsigned char extraBytes) {
   int spare = freeMemory()-extraBytes;
+  if (spare < 0) spare = 0;
   if (spare < minimum_free_memory) minimum_free_memory = spare;
-  return minimum_free_memory;
+}
+
+// Return low memory value.
+int minimumFreeMemory() {
+  byte sreg_save = SREG;
+  noInterrupts(); // Disable interrupts
+  int retval = minimum_free_memory;
+  SREG = sreg_save; // Restore interrupt state
+  return retval;
 }

freeMemory.h

@@ -20,6 +20,6 @@
 
 #ifndef freeMemory_h
 #define freeMemory_h
-int freeMemory();
+void updateMinimumFreeMemory(unsigned char extraBytes=0);
-int updateMinimumFreeMemory(unsigned char extraBytes=0);
+int minimumFreeMemory();
 #endif