Craig Evans
/
ELEC2645_UpDown_Counter_2021
Up Down Counter using FSM
main.cpp
- Committer:
- eencae
- Date:
- 2020-12-10
- Revision:
- 0:7c0953072ecb
File content as of revision 0:7c0953072ecb:
/* 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 }