File content as of revision 5:99594f4ab659:

// L. van der Kolk, ELVEDEKA, Holland //
// File:  buttons.cpp   version  1.0

#include "mbed.h"

#define TRUE  1
#define FALSE 0

extern Serial USB;

int button_flag = 0;

char key_message[20] = "$PCDUKEY,";  // : setup begin of key message string to FS

BusInOut button(p24, p23, p22, p21); // : Mbed buttons as 4 bit bus

void init_buttons_Mbed() {
    // set button bus as input :
    button.input();
    // enable pull up resistors on inputs:
    button.mode(PullUp);
}

void scan_buttons_Mbed() {
static int pushed = FALSE;
  switch (button) {
    case 0xF : {
    // nothing pushed, reset pushed flag:
        pushed = FALSE;
        break;
    }
    
    case 0x7 : {
    // button 1 pushed:
        if ( pushed == FALSE ) button_flag = 1;
        pushed = TRUE;
        break;
    }
    
    case 0xB : {
    // button 2 pushed:
        if ( pushed == FALSE ) button_flag = 2;
        pushed = TRUE;
        break; 
    }   
    
    case 0xD : {
    // button 3 pushed:
        if ( pushed == FALSE ) button_flag = 3;
        pushed = TRUE;
        break;
    }
    
    case 0xE : {
    // button 4 pushed:
        if ( pushed == FALSE ) button_flag = 4;
        pushed = TRUE;
        break;
    }
    
    default :  break;
        
  }
}


void collect_and_send_FSdata() {
    int i;
    char byte_read;
    char exor_byte = 0;
    if ( button_flag != 0 ) {
    //  Create key message:
        i = 9; // : i points to first place after $PCDUKEY, 
        // Add key identifier 'SKEY' and a '*' char to key message string:
        sprintf(&key_message[i],"%s","SKEY");
        // Add 2 digit keynumber and a '*' char :
        i = 13; // : i points to first place after $PCDUKEY,SKEY 
        sprintf(&key_message[i],"%02d*",button_flag);
        // Calculate checksum now : 
        i = 1; // : i points to first place after '$'
        do { byte_read = key_message[i];
             if (byte_read == '*') break; // : exclude '*' from calculation
             exor_byte = exor_byte ^ byte_read;
             i++;
        } while ( i < 20 );
        i++;    // : i now points to first digit of checksum after '*'
        // Add exor_byte in 2 hex digits and a CR + LF:
        sprintf(&key_message[i],"%02x\r\n",exor_byte); // : ! extra NULL char added by sprintf 
        USB.printf("%s",key_message);
        button_flag = 0;
     }
}