Craig Evans
/
2645_FSM_UpDown_Counter
Sample code from ELEC2645 Week 16 Lab Demonstrates how to implement a simple FSM up/down counter
main.cpp
- Committer:
- eencae
- Date:
- 2017-12-20
- Revision:
- 1:fb324de02b7f
- Parent:
- 0:c5278b91719f
File content as of revision 1:fb324de02b7f:
/* 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 */ #include "mbed.h" // pre-processor directives // defines directions as 0/1. Note UPPERCASE #define UP 0 #define DOWN 1 // K64F on-board LEDs DigitalOut r_led(LED_RED); DigitalOut g_led(LED_GREEN); DigitalOut b_led(LED_BLUE); // K64F on-board switches InterruptIn sw2(SW2); InterruptIn sw3(SW3); // Gamepad Button A InterruptIn buttonA(PTB9); // LEDs on Gamepad (1 to 4) - active-low 0 = on and 1 = off BusOut output(PTA1,PTA2,PTC2,PTC3); // array of states in the FSM, each element is the output of the counter // set the output in binary to make it easier, 0 is LED on, 1 is LED off int fsm[4] = {0b0111,0b1011,0b1101,0b1110}; // flag - must be volatile as changes within ISR // g_ prefix makes it easier to distinguish it as global volatile int g_buttonA_flag = 0; // function prototypes // set-up the on-board LEDs and switches void init_K64F(); // Button A interrupt service routine void buttonA_isr(); int main() { // initialise on-board LED and switches init_K64F(); // Button A is connected between the pin and 3.3 V, we therefore need to turn on the internal pull-down resister buttonA.mode(PullDown); // It will return 0 by default and a 1 when pressed i.e. cause a rising edge buttonA.rise(&buttonA_isr); // 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 = 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 // or could jump to starting state i.e. state = 0 break; } wait(0.5); // small delay } } void init_K64F() { // on-board LEDs are active-low, so set pin high to turn them off. r_led = 1; g_led = 1; b_led = 1; // since the on-board switches have external pull-ups, we should disable the internal pull-down // resistors that are enabled by default using InterruptIn sw2.mode(PullNone); sw3.mode(PullNone); } // Button A event-triggered interrupt void buttonA_isr() { g_buttonA_flag = 1; // set flag in ISR }