Diff: main.cpp

Revision:

0:c49a2dd99fc3

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Fri Sep 20 14:06:30 2019 +0000
@@ -0,0 +1,85 @@
+#include "mbed.h"
+void countUp();
+void countDown();
+
+#define N 1000000
+#define RELEASED 0
+#define PRESSED  1
+
+//Hardware
+DigitalOut red_led(PE_15);     //CountUp is in its critical section
+DigitalOut yellow_led(PB_10);  //CountDown is in its critical section
+DigitalOut green_led(PB_11);   //counter != 0
+DigitalIn button(USER_BUTTON);
+
+//Additional Threads
+Thread t1;
+Thread t2;
+
+//Shared mutable state
+volatile long long counter = 0; //Volatile means it must be stored in memory
+
+//Increment the shared variable 
+void countUp()
+{
+    //RED MEANS THE COUNT UP FUNCTION IS IN ITS CRITICAL SECTION
+    red_led = 1;
+    for (unsigned int n=0; n<N; n++) {
+        counter++; 
+        counter++;
+        counter++;
+        counter++;
+        counter++;
+        counter++;
+        counter++;
+        counter++;
+        counter++;
+        counter++;           
+    }  
+    red_led = 0; 
+    
+}
+
+//Decrement the shared variable
+void countDown()
+{
+    //YELLOW MEANS THE COUNT DOWN FUNCTION IS IN ITS CRITICAL SECTION
+    yellow_led = 1;
+    for (unsigned int n=0; n<N; n++) {
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;
+        counter--;           
+    }
+    yellow_led = 0;
+          
+}
+int main() {
+    
+    green_led = 1;
+    
+    //Start competing threads
+    t1.start(countUp);
+    t2.start(countDown);
+    
+    //These threads DO exit, so let's wait for BOTH to finish
+    t1.join();  //Wait for thread t1 to finish
+    t2.join();  //Wait for thread t2 to finish
+    
+    //Did the counter end up at zero?
+    if (counter == 0) {
+        green_led = 0;   
+    }
+        
+    //Now spin-lock for ever
+    while(1) { 
+        asm("nop");
+    };
+}
+