main.cpp

00001 #include "mbed.h"
00002 #define N 100000
00003 #define RELEASED 1
00004 #define PRESSED  0
00005 DigitalOut red_led(D7);     //CountUp is in its critical section
00006 DigitalOut yellow_led(D6);  //CountDown is in its critical section
00007 DigitalOut green_led(D5);   //counter != 0
00008 DigitalIn button(USER_BUTTON);
00009 
00010 //Shared mutable state
00011 volatile long long counter = 0; //Volatile means it must be stored in memory
00012 
00013 //Increment the shared variable 
00014 void countUp()
00015 {
00016     //RED MEANS THE COUNT UP FUNCTION IS IN ITS CRITICAL SECTION
00017     red_led = 1;
00018     for (int n=0; n<N; n++) {
00019         counter++; 
00020         counter++;
00021         counter++;
00022         counter++;
00023         counter++;
00024         counter++;
00025         counter++;
00026         counter++;
00027         counter++;
00028         counter++;           
00029     }  
00030     red_led = 0; 
00031     
00032     //Last to finish turnes out the green light
00033     if (counter == 0) {
00034         green_led = 0;   
00035     }
00036 }
00037 
00038 //Decrement the shared variable
00039 void countDown()
00040 {
00041     //YELLOW MEANS THE COUNT DOWN FUNCTION IS IN ITS CRITICAL SECTION
00042     yellow_led = 1;
00043     for (int n=0; n<N; n++) {
00044         counter--;
00045         counter--;
00046         counter--;
00047         counter--;
00048         counter--;
00049         counter--;
00050         counter--;
00051         counter--;
00052         counter--;
00053         counter--;           
00054     }
00055     yellow_led = 0;
00056       
00057     //Last to finish turns out the green light  
00058     if (counter == 0) {
00059         green_led = 0;   
00060     }     
00061 }
00062 int main() {
00063     
00064     green_led = 1;
00065     Timeout t1;
00066     
00067     // TRY EACH OF THESE LINES IN TURN.
00068     // ALL IT DOES IS CHANGE THE TIMING OF THE ISR, NOT THE FUNCTION
00069 
00070     if (button == PRESSED) {
00071         //VERSION 2: short delay allowing main to be preempted - you might want to tweak this value
00072         t1.attach_us(&countDown, 15);
00073     } else {
00074         //VERSION 1: 2s - ENOUGH TIME FOR COUNTUP TO FINISH
00075         t1.attach(&countDown, 2);                   
00076     }
00077     
00078     //Run count up on the main thread
00079     countUp();
00080     
00081     //Now spin-lock for ever
00082     while(1) { 
00083         asm("nop");
00084     };
00085 }
00086