Diff: main.cpp

Revision:

1:13e0c1956b54

Parent:

0:a66a8cb0012c

Child:

2:071f22412cdc

diff -r a66a8cb0012c -r 13e0c1956b54 main.cpp
--- a/main.cpp	Mon Jan 23 13:53:49 2017 +0000
+++ b/main.cpp	Mon Jan 23 17:26:17 2017 +0000
@@ -1,65 +1,39 @@
 #include "mbed.h"
 #include "rtos.h"
 
-// Labs 2: Example program for polling an input
-// --------------------------------------------
-// The program uses a thread to poll a digital input
-//   - The thread monitors the position of the button
-//   - When the button transitions up and down, a press event is signaled 
-//   - Button bounce is guarded against
-// A second thread checks for the press event and toggles the LED
+// Labs 2: Example program for using an interrupt (or callback)
+// -----------------------------------------------------------
+// A callback function (corresponding to an ISR) is called when a button 
+//    is pressed
+// The callback uses a shared variable to signal another thread
 
-DigitalIn button(PTD0, PullUp);
+InterruptIn button(PTD0);
 DigitalOut led(LED_RED);
 
-Thread pollT ; // thread to poll
-Thread flashT ; // thread to flash light
-volatile int pressEvent = 0 ;  // Variabe set by the polling thread
+Thread flashT ;
+volatile int pressEvent = 0 ;
 
-enum buttonPos { up, down, bounce }; // Button positions
-void polling() {
-    buttonPos pos = up ;
-    int bcounter = 0 ;
-    while (true) {
-        switch (pos) {
-            case up :
-                if (button == 1) {    // now down 
-                    pressEvent = 1 ;  // transition occurred
-                    pos = down ;
-                }
-                break ;
-            case down : 
-                if (button == 0) { // no longer down
-                    bcounter = 3 ; // wait four cycles
-                    pos = bounce ;
-                }
-                break ;
-            case bounce :
-                if (button == 1) { // down again - button has bounced
-                    pos = down ;   // no event
-                } else if (bcounter == 0) {
-                    pos = up ;     // delay passed - reset to up
-                } else {
-                    bcounter-- ;   // continue waiting
-                }
-                break ;
-        }
-        Thread::wait(30);
-    }
+// Signal when the button is pressed
+//   Note: bounce may occur 
+void buttonCallback(){
+    pressEvent = 1 ;
 }
 
 // Toggle the LED every time the button is pressed
+//    Note: the LED could be toggled in the callback 
 void flash() {
     while(true) {
         if (pressEvent) {
-            pressEvent = 0 ; // clear the event variable
             led = !led ;
+            pressEvent = 0 ; // Clear the event variable
         }
         Thread::wait(100) ;
     }
 }
 
 int main() {
-    pollT.start(&polling) ; // start the polling thread running 
-    flashT.start(&flash) ; // start the flashing thread running 
+    button.mode(PullUp);             // Ensure button i/p has pull up
+    button.rise(&buttonCallback) ;   // Attach function to rise event
+
+    flashT.start(&flash) ; // Start the flashing thread running 
 }
\ No newline at end of file