main.cpp

00001 #include "mbed.h"
00002 
00003 // Labs 2: Example program for polling an input
00004 // --------------------------------------------
00005 // The program uses a thread to poll a digital input
00006 //   - The thread monitors the position of the button
00007 //   - When the button transitions up and down, a press event is signaled 
00008 //   - Button bounce is guarded against
00009 // A second thread (the default one) checks for the press event and toggles the LED
00010 
00011 DigitalIn b1(PTD0, PullUp);
00012 DigitalOut led(LED1);
00013 
00014 Thread pollT ; // thread to poll
00015 volatile int pressEvent = 0 ;  // Variabe set by the polling thread
00016   // Sharing a global variable between two threads is not safe in general
00017   //  but it can be ok if a) update is atomic and b) only one thread writes
00018 
00019 enum buttonPos { up, down, bounce }; // Button positions
00020 void polling() {
00021     buttonPos pos = up ;
00022     int bcounter = 0 ;
00023     
00024     while (true) {
00025         ThisThread::sleep_for(30) ; // poll every 30ms
00026         switch (pos) {
00027             case up :
00028                 if (!b1.read()) {    // now down 
00029                     pressEvent = 1 ;  // transition occurred
00030                     pos = down ;
00031                 }
00032                 break ;
00033             case down : 
00034                 if (b1 == 1) { // no longer down
00035                     bcounter = 3 ; // wait four cycles
00036                     pos = bounce ;
00037                 }
00038                 break ;
00039             case bounce :
00040                 if (b1 == 0) { // down again - button has bounced
00041                     pos = down ;   // no event
00042                 } else if (bcounter == 0) {
00043                     pos = up ;     // delay passed - reset to up
00044                 } else {
00045                     bcounter-- ;   // continue waiting
00046                 }
00047                 break ;
00048         }
00049     }
00050 }
00051 
00052 /*  ---- Main function (default thread) ----
00053     Note that if this thread completes, nothing else works
00054  */
00055 int main() {
00056     led = 1 ;  // Initially off
00057     //int time [4] = {200,400,600,800,1000 };
00058     pollT.start(callback(polling));
00059     int rate=200;
00060     while(true) {
00061         //if (pressEvent) {
00062 
00063             led = !led ;
00064             
00065         //}
00066         if(pressEvent) {
00067             rate += 200;
00068             pressEvent = 0 ; // clear the event variable
00069         }    
00070         if (rate>1000){
00071             rate=200;
00072             }
00073             
00074         ThisThread::sleep_for(rate) ; // delay for 100ms 
00075     }
00076 }