ledtoggle.c - Uses an FSM approach to toggle an LED whenever a pushbutton input is pressed and released.

A program that uses a finite state machine approach for toggling an LED whenever a pushbutton switch is pressed and released. Demonstrates the use of debounce delays when polling a switch input.

 
#include "pic24_all.h"
 

LED1 configuration and access

#define CONFIG_LED1() CONFIG_RB14_AS_DIG_OUTPUT()
#define LED1 (_LATB14)     //led1 state
 

Pushbutton configuration and access

void config_pb()  {
#if (HARDWARE_PLATFORM == EMBEDDED_C1)
  CONFIG_RB7_AS_DIG_INPUT();
  ENABLE_RB7_PULLUP();
#else
  CONFIG_RB13_AS_DIG_INPUT();
  ENABLE_RB13_PULLUP();
#endif

Give the pullup some time to take effect.

  DELAY_US(1);
}

#if (HARDWARE_PLATFORM == EMBEDDED_C1)
# define PB_PRESSED()   (_RB7 == 0)
# define PB_RELEASED()  (_RB7 == 1)
#else
# define PB_PRESSED()   (_RB13 == 0)
# define PB_RELEASED()  (_RB13 == 1)
#endif
 

State machine

First, define the states, along with a human-readable version.

 
typedef enum  {
  STATE_PRESSED,
  STATE_RELEASED,
} state_t;

const char* apsz_state_names[] = {
  "STATE_PRESSED",
  "STATE_RELEASED",
};
 

Provide a convenient function to print out the state.

void print_state(state_t e_state) {

Force an initial print of the state

  static state_t e_last_state = 0xFFFF;
 

Only print if the state changes.

  if (e_state != e_last_state) {
    e_last_state = e_state;

Verify that the state has a string representation before printing it.

    ASSERT(e_state <= N_ELEMENTS(apsz_state_names));
    outString(apsz_state_names[e_state]);
    outChar('\n');
  }
}
 

This function defines the state machine.

void update_state(void) {
  static state_t e_state = STATE_RELEASED;

  switch (e_state) {
    case STATE_RELEASED:
      if (PB_PRESSED()) {
        e_state = STATE_PRESSED;
        LED1 = !LED1;
      }
      break;

    case STATE_PRESSED:
      if (PB_RELEASED()) {
        e_state = STATE_RELEASED;
      }
      break;

    default:
      ASSERT(0);
  }

  print_state(e_state);
}
 

main

This code initializes the system, then runs the state machine above when the pushbutton’s value changes.

int main (void) {

Configure the hardware.

  configBasic(HELLO_MSG);
  config_pb();
  CONFIG_LED1();
 

Initialize the state machine’s extended state to its starting value.

  LED1 = 0;

  while (1) {
    update_state();
 

Debounce the switch by waiting for bounces to die out.

    DELAY_MS(DEBOUNCE_DLY);
 

Blink the heartbeat LED to confirm that the program is running.

    doHeartbeat();
  }
}