Anastasios Barlas / Mbed OS digitalInPolling_sample

Lab2 part 1

Fork of digitalInPolling_sample by William Marsh

main.cpp@0:a66a8cb0012c, 2017-01-23 (annotated)

Committer:
WilliamMarshQMUL
Date:
Mon Jan 23 13:53:49 2017 +0000
Revision:
0:a66a8cb0012c
Child:
1:4709af498799
First sample version

Who changed what in which revision?

UserRevisionLine numberNew contents of line
WilliamMarshQMUL 0:a66a8cb0012c 1 #include "mbed.h"
WilliamMarshQMUL 0:a66a8cb0012c 2 #include "rtos.h"
WilliamMarshQMUL 0:a66a8cb0012c 3
WilliamMarshQMUL 0:a66a8cb0012c 4 // Labs 2: Example program for polling an input
WilliamMarshQMUL 0:a66a8cb0012c 5 // --------------------------------------------
WilliamMarshQMUL 0:a66a8cb0012c 6 // The program uses a thread to poll a digital input
WilliamMarshQMUL 0:a66a8cb0012c 7 // - The thread monitors the position of the button
WilliamMarshQMUL 0:a66a8cb0012c 8 // - When the button transitions up and down, a press event is signaled
WilliamMarshQMUL 0:a66a8cb0012c 9 // - Button bounce is guarded against
WilliamMarshQMUL 0:a66a8cb0012c 10 // A second thread checks for the press event and toggles the LED
WilliamMarshQMUL 0:a66a8cb0012c 11
WilliamMarshQMUL 0:a66a8cb0012c 12 DigitalIn button(PTD0, PullUp);
WilliamMarshQMUL 0:a66a8cb0012c 13 DigitalOut led(LED_RED);
WilliamMarshQMUL 0:a66a8cb0012c 14
WilliamMarshQMUL 0:a66a8cb0012c 15 Thread pollT ; // thread to poll
WilliamMarshQMUL 0:a66a8cb0012c 16 Thread flashT ; // thread to flash light
WilliamMarshQMUL 0:a66a8cb0012c 17 volatile int pressEvent = 0 ; // Variabe set by the polling thread
WilliamMarshQMUL 0:a66a8cb0012c 18
WilliamMarshQMUL 0:a66a8cb0012c 19 enum buttonPos { up, down, bounce }; // Button positions
WilliamMarshQMUL 0:a66a8cb0012c 20 void polling() {
WilliamMarshQMUL 0:a66a8cb0012c 21 buttonPos pos = up ;
WilliamMarshQMUL 0:a66a8cb0012c 22 int bcounter = 0 ;
WilliamMarshQMUL 0:a66a8cb0012c 23 while (true) {
WilliamMarshQMUL 0:a66a8cb0012c 24 switch (pos) {
WilliamMarshQMUL 0:a66a8cb0012c 25 case up :
WilliamMarshQMUL 0:a66a8cb0012c 26 if (button == 1) { // now down
WilliamMarshQMUL 0:a66a8cb0012c 27 pressEvent = 1 ; // transition occurred
WilliamMarshQMUL 0:a66a8cb0012c 28 pos = down ;
WilliamMarshQMUL 0:a66a8cb0012c 29 }
WilliamMarshQMUL 0:a66a8cb0012c 30 break ;
WilliamMarshQMUL 0:a66a8cb0012c 31 case down :
WilliamMarshQMUL 0:a66a8cb0012c 32 if (button == 0) { // no longer down
WilliamMarshQMUL 0:a66a8cb0012c 33 bcounter = 3 ; // wait four cycles
WilliamMarshQMUL 0:a66a8cb0012c 34 pos = bounce ;
WilliamMarshQMUL 0:a66a8cb0012c 35 }
WilliamMarshQMUL 0:a66a8cb0012c 36 break ;
WilliamMarshQMUL 0:a66a8cb0012c 37 case bounce :
WilliamMarshQMUL 0:a66a8cb0012c 38 if (button == 1) { // down again - button has bounced
WilliamMarshQMUL 0:a66a8cb0012c 39 pos = down ; // no event
WilliamMarshQMUL 0:a66a8cb0012c 40 } else if (bcounter == 0) {
WilliamMarshQMUL 0:a66a8cb0012c 41 pos = up ; // delay passed - reset to up
WilliamMarshQMUL 0:a66a8cb0012c 42 } else {
WilliamMarshQMUL 0:a66a8cb0012c 43 bcounter-- ; // continue waiting
WilliamMarshQMUL 0:a66a8cb0012c 44 }
WilliamMarshQMUL 0:a66a8cb0012c 45 break ;
WilliamMarshQMUL 0:a66a8cb0012c 46 }
WilliamMarshQMUL 0:a66a8cb0012c 47 Thread::wait(30);
WilliamMarshQMUL 0:a66a8cb0012c 48 }
WilliamMarshQMUL 0:a66a8cb0012c 49 }
WilliamMarshQMUL 0:a66a8cb0012c 50
WilliamMarshQMUL 0:a66a8cb0012c 51 // Toggle the LED every time the button is pressed
WilliamMarshQMUL 0:a66a8cb0012c 52 void flash() {
WilliamMarshQMUL 0:a66a8cb0012c 53 while(true) {
WilliamMarshQMUL 0:a66a8cb0012c 54 if (pressEvent) {
WilliamMarshQMUL 0:a66a8cb0012c 55 pressEvent = 0 ; // clear the event variable
WilliamMarshQMUL 0:a66a8cb0012c 56 led = !led ;
WilliamMarshQMUL 0:a66a8cb0012c 57 }
WilliamMarshQMUL 0:a66a8cb0012c 58 Thread::wait(100) ;
WilliamMarshQMUL 0:a66a8cb0012c 59 }
WilliamMarshQMUL 0:a66a8cb0012c 60 }
WilliamMarshQMUL 0:a66a8cb0012c 61
WilliamMarshQMUL 0:a66a8cb0012c 62 int main() {
WilliamMarshQMUL 0:a66a8cb0012c 63 pollT.start(&polling) ; // start the polling thread running
WilliamMarshQMUL 0:a66a8cb0012c 64 flashT.start(&flash) ; // start the flashing thread running
WilliamMarshQMUL 0:a66a8cb0012c 65 }