Akhil Nair / Mbed OS Lab2polling

lab 2 part 1

main.cpp@2:cd1fe8c29793, 2018-01-16 (annotated)

Committer:
WilliamMarshQMUL
Date:
Tue Jan 16 18:02:44 2018 +0000
Revision:
2:cd1fe8c29793
Parent:
1:4709af498799
Child:
3:8d87cbabe37e
Corrected for mbed 5

Who changed what in which revision?

UserRevisionLine numberNew contents of line
WilliamMarshQMUL 0:a66a8cb0012c 1 #include "mbed.h"
WilliamMarshQMUL 0:a66a8cb0012c 2
WilliamMarshQMUL 0:a66a8cb0012c 3 // Labs 2: Example program for polling an input
WilliamMarshQMUL 0:a66a8cb0012c 4 // --------------------------------------------
WilliamMarshQMUL 0:a66a8cb0012c 5 // The program uses a thread to poll a digital input
WilliamMarshQMUL 0:a66a8cb0012c 6 // - The thread monitors the position of the button
WilliamMarshQMUL 0:a66a8cb0012c 7 // - When the button transitions up and down, a press event is signaled
WilliamMarshQMUL 0:a66a8cb0012c 8 // - Button bounce is guarded against
WilliamMarshQMUL 2:cd1fe8c29793 9 // A second thread (the default one) checks for the press event and toggles the LED
WilliamMarshQMUL 0:a66a8cb0012c 10
WilliamMarshQMUL 2:cd1fe8c29793 11 DigitalIn b1(PTD0, PullUp);
WilliamMarshQMUL 2:cd1fe8c29793 12 DigitalOut led(LED1);
WilliamMarshQMUL 0:a66a8cb0012c 13
WilliamMarshQMUL 0:a66a8cb0012c 14 Thread pollT ; // thread to poll
WilliamMarshQMUL 0:a66a8cb0012c 15 volatile int pressEvent = 0 ; // Variabe set by the polling thread
WilliamMarshQMUL 0:a66a8cb0012c 16
WilliamMarshQMUL 0:a66a8cb0012c 17 enum buttonPos { up, down, bounce }; // Button positions
WilliamMarshQMUL 0:a66a8cb0012c 18 void polling() {
WilliamMarshQMUL 0:a66a8cb0012c 19 buttonPos pos = up ;
WilliamMarshQMUL 0:a66a8cb0012c 20 int bcounter = 0 ;
WilliamMarshQMUL 0:a66a8cb0012c 21 while (true) {
WilliamMarshQMUL 0:a66a8cb0012c 22 switch (pos) {
WilliamMarshQMUL 0:a66a8cb0012c 23 case up :
WilliamMarshQMUL 2:cd1fe8c29793 24 if (!b1.read()) { // now down
WilliamMarshQMUL 0:a66a8cb0012c 25 pressEvent = 1 ; // transition occurred
WilliamMarshQMUL 0:a66a8cb0012c 26 pos = down ;
WilliamMarshQMUL 0:a66a8cb0012c 27 }
WilliamMarshQMUL 0:a66a8cb0012c 28 break ;
WilliamMarshQMUL 0:a66a8cb0012c 29 case down :
WilliamMarshQMUL 2:cd1fe8c29793 30 if (b1 == 1) { // no longer down
WilliamMarshQMUL 0:a66a8cb0012c 31 bcounter = 3 ; // wait four cycles
WilliamMarshQMUL 0:a66a8cb0012c 32 pos = bounce ;
WilliamMarshQMUL 0:a66a8cb0012c 33 }
WilliamMarshQMUL 0:a66a8cb0012c 34 break ;
WilliamMarshQMUL 0:a66a8cb0012c 35 case bounce :
WilliamMarshQMUL 2:cd1fe8c29793 36 if (b1 == 0) { // down again - button has bounced
WilliamMarshQMUL 0:a66a8cb0012c 37 pos = down ; // no event
WilliamMarshQMUL 0:a66a8cb0012c 38 } else if (bcounter == 0) {
WilliamMarshQMUL 0:a66a8cb0012c 39 pos = up ; // delay passed - reset to up
WilliamMarshQMUL 0:a66a8cb0012c 40 } else {
WilliamMarshQMUL 0:a66a8cb0012c 41 bcounter-- ; // continue waiting
WilliamMarshQMUL 0:a66a8cb0012c 42 }
WilliamMarshQMUL 0:a66a8cb0012c 43 break ;
WilliamMarshQMUL 0:a66a8cb0012c 44 }
WilliamMarshQMUL 0:a66a8cb0012c 45 Thread::wait(30);
WilliamMarshQMUL 0:a66a8cb0012c 46 }
WilliamMarshQMUL 0:a66a8cb0012c 47 }
WilliamMarshQMUL 0:a66a8cb0012c 48
WilliamMarshQMUL 2:cd1fe8c29793 49 /* ---- Main function (default thread) ----
WilliamMarshQMUL 2:cd1fe8c29793 50 Note that if this thread completes, nothing else works
WilliamMarshQMUL 2:cd1fe8c29793 51 */
WilliamMarshQMUL 2:cd1fe8c29793 52 int main() {
WilliamMarshQMUL 2:cd1fe8c29793 53 led = 1 ; // Initially off
WilliamMarshQMUL 2:cd1fe8c29793 54 pollT.start(callback(polling));
WilliamMarshQMUL 2:cd1fe8c29793 55
WilliamMarshQMUL 0:a66a8cb0012c 56 while(true) {
WilliamMarshQMUL 0:a66a8cb0012c 57 if (pressEvent) {
WilliamMarshQMUL 0:a66a8cb0012c 58 pressEvent = 0 ; // clear the event variable
WilliamMarshQMUL 0:a66a8cb0012c 59 led = !led ;
WilliamMarshQMUL 0:a66a8cb0012c 60 }
WilliamMarshQMUL 0:a66a8cb0012c 61 Thread::wait(100) ;
WilliamMarshQMUL 0:a66a8cb0012c 62 }
WilliamMarshQMUL 0:a66a8cb0012c 63 }