Craig Evans
/
ELEC2645_UpDown_Counter_2021
Up Down Counter using FSM
Diff: main.cpp
- Revision:
- 0:7c0953072ecb
diff -r 000000000000 -r 7c0953072ecb main.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/main.cpp Thu Dec 10 13:42:11 2020 +0000 @@ -0,0 +1,126 @@ +/* + +2645_FSM_UpDown_Counter + +Sample code from ELEC2645 + +Demonstrates how to implement a simple FSM up/down counter + +(c) Craig A. Evans, University of Leeds, Jan 2016 +Updated Jan 2020 +Updated Dec 2020 + +*/ + +#include "mbed.h" +#include "platform/mbed_thread.h" + +// defines directions as 0/1. Note UPPERCASE +#define UP 0 +#define DOWN 1 + +// create a bus for writing to the output (LEDs) at once +BusOut output(LED4,LED3,LED2,LED1); +// Button A on board +InterruptIn buttonA(p29); + +// array of states in the FSM, each element is the output of the counter +// set the output in binary to make it easier, 1 is LED on, 0 is LED off +int g_fsm[4] = {0b0001,0b0010,0b0100,0b1000}; + +// flag - must be volatile as changes within ISR +// g_ prefix makes it easier to distinguish it as global +volatile int g_buttonA_flag = 0; + +// Button A interrupt service routine +void buttonA_isr(); + +int main() +{ + // Button A has a pull-down resistor, so the pin will be at 0 V by default + // and rise to 3.3 V when pressed. We therefore need to look for a rising edge + // on the pin to fire the interrupt + buttonA.rise(&buttonA_isr); + // since Button A has an external pull-down, we should disable to internal pull-down + // resistor that is enabled by default using InterruptIn + buttonA.mode(PullNone); + + // set inital state + int state = 0; + // set initial direction + int direction = UP; + + while(1) { // loop forever + + // check if flag i.e. interrupt has occured + if (g_buttonA_flag) { + g_buttonA_flag = 0; // if it has, clear the flag + + // swap direction when button has been pressed + // (could just use ! but want this to be explicit to aid understanding) + if (direction == UP) { + direction = DOWN; + } else { + direction = UP; + } + } + + output = g_fsm[state]; // output current state + + // check which state we are in and see which the next state should be next depending on direction + switch(state) { + case 0: + switch(direction) { + case UP: + state = 1; + break; + case DOWN: + state = 3; + break; + } + break; + case 1: + switch(direction) { + case UP: + state = 2; + break; + case DOWN: + state = 0; + break; + } + break; + case 2: + switch(direction) { + case UP: + state = 3; + break; + case DOWN: + state = 1; + break; + } + break; + case 3: + switch(direction) { + case UP: + state = 0; + break; + case DOWN: + state = 2; + break; + } + break; + default: // default case + error("Invalid state!"); //invalid state - call error routine + state = 0; + break; + } + + thread_sleep_for(500); + } +} + +// Button A event-triggered interrupt +void buttonA_isr() +{ + g_buttonA_flag = 1; // set flag in ISR +} \ No newline at end of file