Add switch to avoid using malloc() for SPI irq map

Based on 7c8bab702 by Martin.Thomaz@atmel.com

Author: facchinm

libraries/SPI/src/SPI.cpp

@@ -88,9 +88,12 @@ void SPIClass::usingInterrupt(int interruptNumber)
     interruptMode = SPI_IMODE_GLOBAL;
   else
   {
-    if (irqMap == NULL) {
-      irqMap = (uint8_t*)malloc(EXTERNAL_NUM_INTERRUPTS);
-    }
+    #ifdef USE_MALLOC_FOR_IRQ_MAP
+      if (irqMap == NULL) {
+        irqMap = (uint8_t*)malloc(EXTERNAL_NUM_INTERRUPTS);
+      }
+    #endif
+
     interruptMode |= SPI_IMODE_EXTINT;
     if (interruptNumber < 32) {
       interruptMask_lo |= 1 << interruptNumber;
@@ -116,8 +119,10 @@ void SPIClass::notUsingInterrupt(int interruptNumber)
 
   if (interruptMask_lo == 0 && interruptMask_hi == 0) {
     interruptMode = SPI_IMODE_NONE;
-    free(irqMap);
-    irqMap = NULL;
+    #ifdef USE_MALLOC_FOR_IRQ_MAP
+      free(irqMap);
+      irqMap = NULL;
+    #endif
   }
 }
 
@@ -181,8 +186,8 @@ void SPIClass::beginTransaction(SPISettings settings)
     {
       detachMaskedInterrupts();
     }
-  config(settings);
   }
+  config(settings);
 }
 
 void SPIClass::endTransaction(void)

libraries/SPI/src/SPI.h

@@ -22,6 +22,10 @@
 
 #include <Arduino.h>
 
+#ifndef USE_MALLOC_FOR_IRQ_MAP
+#define USE_MALLOC_FOR_IRQ_MAP  1
+#endif
+
 // SPI_HAS_TRANSACTION means SPI has
 //   - beginTransaction()
 //   - endTransaction()
@@ -161,6 +165,7 @@ class SPIClass {
   void setClockDivider(uint8_t uc_div);
 
   private:
+
   void init();
   void config(SPISettings settings);
 
@@ -184,9 +189,15 @@ class SPIClass {
   char interruptSave;
   uint32_t interruptMask_lo;
   uint32_t interruptMask_hi;
-  uint8_t* irqMap = NULL;
+
+  #if USE_MALLOC_FOR_IRQ_MAP
+    uint8_t* irqMap = NULL;
+  #else
+    volatile uint8_t irqMap[EXTERNAL_NUM_INTERRUPTS];
+  #endif
 };
 
+
 #if SPI_INTERFACES_COUNT > 0
   extern SPIClass SPI;
 #endif
@@ -199,4 +210,4 @@ class SPIClass {
 #define SPI_CLOCK_DIV64     ( SPI_PRESC_DIV64_gc                    )
 #define SPI_CLOCK_DIV128    ( SPI_PRESC_DIV128_gc                   )
 
-#endif
+#endif