File content as of revision 6:e0bf3b244d7c:

// L. van der Kolk, ELVEDEKA, Holland //
// File:  USB_receive_2.cpp Mbos version

#include "mbed.h"
#include "MODSERIAL.h" // : Note: import lib of Erk Olieman V1.25 to prevent compiler error!

// Instantiate USB communication defined by Mbed USB TX and RX lines
// with TX and RX ringbuffers :
MODSERIAL USB(USBTX, USBRX, 256, 512);   
   
void decode_string(int nummer_of_chars);
void read_datafields(int command_number);

#define max_string_length 80 // : max length of received string starting with $ and ending with CR/LF
#define min_string_length 10 // : min length of received string starting with $ and ending with CR/LF
char string_received[max_string_length + 2]; // : holds received string starting with $ and ending with CR/LF

int  receive_flag = false;   // :  global flag, signals a receive 'event' 

#define max_commas 10  // : max. nr of possible field separating commas in a valid message string to CDU
int comma[max_commas];      // : array with positions of all found commas in string_receved[]
#define message_header "$PCDU"  // : common message header in all messages

#define max_nr_of_commands 16   // : max nr of possible FS-to-CDU commands
// Define array of pointers to possible FS-to-CDU commands with 3 characters:
const char *command[max_nr_of_commands] = {
   "123",    // : no valid CDU command nr. 0 , used for debugging only
   "MSG",    // : command nr. 1
   "EXC",    // : command nr. 2
   "BLT",    // : command nr. 3
   "SBY",    // : command nr. 4
   "CLS",    // : command nr. 5
   "SBC",    // : command nr. 6
   "WTX",    // : command nr. 7
   "ETX",    // : command nr. 8
   "KTX",    // : command nr. 9
   "STV",    // : command nr. 10
   "GTV",    // : command nr. 11
};

void collect_FSdata()  {
     // Function reads data from the RX buffer
     // and collects strings starting with $ and ending with CR/LF.
     // Strings shorter than min_string_length or longer than
     // max_string_length will be ignored, others will be decoded further.
    static int $_detected = false;      // : no valid begin of string detected (init only on first call)
    static int string_pntr = 0;         // : pointer at begin of string (init only on first call)
    static int nr_of_received_char = 0; // : counter of received characters (init only on first call)
    char rx_char;
             
    while ( !USB.rxBufferEmpty() )
    {    rx_char = USB.getc(); // : get a char from Rx buffer
        //USB.putc(rx_char);    // : unprotected (!) immediate echo of char in case of debugging  <<<
        // Check for string starting with $ char:
        if ( rx_char == '$' && $_detected == false ){
            $_detected = true;  // : begin of string is detected 
            string_pntr = 0;    // : set pointer to begin of string_received[] buffer
        }
        string_received[string_pntr] = rx_char;
        string_pntr++;
        
        if (string_pntr >= max_string_length) {
            // command string looks too long, so start all over again:
            string_pntr = 0;  // : set pointer back to begin of string_received[] again
            nr_of_received_char = 0;   // : reset number of received chars
            $_detected = false;
        }
    
        if ( rx_char == '\n' && $_detected == true ) { 
            if ( string_pntr > min_string_length ) { // : check minimum string length 
                // Received string can be interesting now because
                // it starts with '$' AND it ends on New-Line  AND
                // it has a minimum length AND it is not too long:
                string_received[string_pntr] = '\0'; // : mark end of string
                //  USB.printf("string_received : %s",string_received );  // show string for debugging <<
                nr_of_received_char = string_pntr;
                //Call decoder to analyse this string:
                decode_string(nr_of_received_char);
                  
                // Get ready for receiving new commands:
                $_detected = false;
                string_pntr = 0;  // : set pointer back to begin of string_received[] again
                nr_of_received_char = 0;   // : reset number of received chars
            }
            else {
                $_detected = false;  
                string_pntr = 0; // : set pointer back to begin of string_received[] again
                nr_of_received_char = 0;   // : reset number of received chars
            }
         }
    } 
}
    
void decode_string(int nummer_of_chars)
{   // -- This function decodes a received $.....CR/LF string written in string_received[] --
    // First it checks for a valid checksum and reads the positions of commas in the string.
    // When checksum is OK, it will continue to look for valid 3 char FS-to-CDU commands.
    // When a valid command is found, data fields will be analyzed further using the found positions
    // of commas in the string.
    int  i,c, equal;
    char byte_read, exor_byte;
    char command_string[6], received_checksum[4], calc_checksum[4];
      
    // Get checksum and position of commas in string_received[] :
    exor_byte = 0;
    i = 1;  // : i points to first char after $
    c = 1;  // : position of first comma
      do {
          byte_read = string_received[i];
          if (byte_read == ',' && c < max_commas) {
              comma[c] = i;
              c++;
          }
          if (byte_read == '*') break;
          exor_byte = exor_byte ^ byte_read;
          i++;
      } while ( i < nummer_of_chars );
    //USB.printf("commas found : %d\n",c-1 );  // : show commas for debugging <<<<<<
    i++;   // : i points to first checksum char after * char
    strncpy(received_checksum,&string_received[i],2);   // : copy 2 char checksum after * 
    // Get calculated checksum by transforming exor_byte in 2 hex chars (with upper case A-F) :
    sprintf(calc_checksum,"%02X",exor_byte); // : + extra NULL char added by sprintf 
    equal = strncmp(received_checksum,calc_checksum,2);
    if (equal != 0) { 
       //USB.printf("checksum is NOT OK ! \n" );  // : show message for debugging <<<
    }
    else { // checksum is OK, go on:
       // Check for 5 char "$PCDU" header:
       equal = strncmp(string_received,message_header,strlen(message_header));
        if (equal != 0) {
            // USB.printf("no $PCDU header in message !\n" );  // : show message for debugging <<<
        }
        else {
             // Read 3 char command after message_header:
             strncpy(command_string,&string_received[strlen(message_header)],3);
             //USB.printf("command found : %3s\n",command_string );  // : show command for debugging <<<
             // Compare found string with known 3 char command list:
             i = 0; 
               do {
                  equal = strncmp(&command_string[0],command[i],3);
                  if( equal == 0) break;
                  i++;
               } while ( i < max_nr_of_commands);
              //USB.printf("command number is : %d\n",i );  // : show command nr for debugging <<<
             if (equal == 0) {
                 // Command is known now, so now read all data fields:
                 read_datafields(i);
             }
        } 
    } 
    
   receive_flag = false;
 }