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Help on RS232 and string

 
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morind79



Joined: 11 Apr 2008
Posts: 2

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Help on RS232 and string
PostPosted: Sun May 02, 2010 10:55 am     Reply with quote
Hi all,

I am sorry, I did some C coding a long time ago, and I need to create a program but it does not work.

Here is what I want to do : the Pic receive data from the serial port, and it should get some value from it.

Here is the data received :
Quote:

TDETAT 000000 B
ADCO 050622013932 8
OPTARIF HC.. <
ISOUSC 45 ?
HCHC 000000000 F
HCHP 000000001 T
PTEC HP..
IINST 000 W
IMAX 000 ?
PAPP 00000 !
HHPHC A ,


I want to get the HCHC and HCHP value 000000000 and 000000001 respectively.

Here is my code:
Code:

char etiquettes[12][16] = {"ADCO", "OPTARIF", "ISOUSC", "HCHP", "HCHC", "PTEC", "IINST", "IMAX", "PAPP", "HHPHC", "MOTDETAT", "ADPS"} ;
char valeurs[12][18];
char checksum[255];
char ligne[30];
int res;

/*------------------------------------------------------------------------------*/
/* Test checksum d'un message (Return 1 si checkum ok)            */
/*------------------------------------------------------------------------------*/
int checksum_ok(char *etiquette, char *valeur, char checksum)
{
   unsigned char sum=32 ;      // Somme des codes ASCII du message + un espace
   int i ;
 
   for (i=0; i<strlen(etiquette); i++) sum=sum+etiquette[i];
   for (i=0; i<strlen(valeur); i++) sum=sum+valeur[i];
   sum=(sum&63)+32;
   if (sum==checksum) return 1;   // Return 1 si checkum ok.
   //syslog(LOG_INFO, "Checksum lu:%02x   calculé:%02x", checksum, sum) ;
   return 0;
}

char *readSerial(char *key)
{
  char sep[3], *ptr;
  char car_prec;
  char ch;
  int id, i=0;
  // Space is the separator
  strcpy(sep," ");
  // Read data (0d 03 02 0a => end transmission and start of a new one)
  do
  {
    car_prec=ch;
   ch=getc();
  }
  while (!(ch==0x02 && car_prec==0x03));  // Wait for the end and begining of transmission
  do
  {
    ch=getc();
  }
  while (ch!=0x03);                      // Wait for the end of transmission.
  for (id=0; id<12; id++)
  {
    // Read the complete line
     gets(ligne);
     // Split ligne in 3, separator is space
     ptr = strtok(ligne, sep);
     while (ptr!=0)
    {
      // 3 fields to read
      if (i<3)
      {
        if (i==0) strcpy(etiquettes[id], ptr);
        if (i==1) strcpy(valeurs[id], ptr);
        if (i==2) strcpy(checksum, ptr);
        i++;
      }
      ptr = strtok(0, sep);
    }
    // Test if the checksum is correct   
     if (!checksum_ok(etiquettes[id], valeurs[id], checksum[0]))
     {
      // Test if the value is the one we are interested of
      if (etiquettes[id]==key)
      {
        return(valeurs[id]);
      }
     }
  }
   
}

I am prety sure the code is not correct (pointer...)

If you have some advices :-)

Thanks

Denis
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Sun May 02, 2010 4:13 pm     Reply with quote
A few comments:
1)
Code:
(etiquettes[id]==key)
This is not the right method for comparing strings. Use strcmp instead.

2) If you don't find a match the function is exited without a return value.

3) You are reading a fixed number of 12 lines. I only count 11, or is the line with code 0x03 also terminated by a newline character? Better would be to change the code and not to assume a fixed number of lines but to read until a 0x03 is found. This way you can also reduce memory consumption by not declaring all arrays as 12 but only use a single array for each type.

4)
Code:
  do
  {
    car_prec=ch;
   ch=getc();
  }
  while (!(ch==0x02 && car_prec==0x03));  // Wait for the end and begining of transmission
  do
  {
    ch=getc();
  }
  while (ch!=0x03);                      // Wait for the end of transmission.
you are waiting for a new message to start, but then you skip another whole message. Why?
morind79



Joined: 11 Apr 2008
Posts: 2

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PostPosted: Mon May 03, 2010 1:26 am     Reply with quote
Hi,

Thank you for your answer. I rewrite this part of code completely here is the new code :

Code:

// Here is the description of a transmission :
//
// 0x02
// LF (0x0A) Label (4 to 8 characters) SP (0x20) Data (1 to 12 charaters) SP (0x20) CRC (Character control) CR (0x0D)
// ...
// 0x03

char *readSerial(char *key)
{
  char label[10];
  char data[14];
  char crc;
  int il, id;
  char ch;
  int field=0;
  // Empty strings
  label[0]='\0';
  data[0]='\0';
  crc='\0';
  // Loop waiting for the beginning of transmission (0x02)
  do
  {
    ch=getc();
  }
  while (ch!=0x02);
  // Read until end of transmission (0x03)
  do
  {
    ch=getc();
    // End of field line 0x0D
    if (ch==0x0D)
    {
      field=0;
      if (!checksum_ok(label, data, crc))
       {
        // Test if this is the required key
        if (strcmp(label, key)==0)
        {
          return(data);
        }
      }   
    }
    // Get field 1 (Label)
    if ((field==1) && (ch!=0x20))
    {
      label[il]=ch;
      il++;   
    }
    // Get field 2 (Data)
    if ((field==2) && (ch!=0x20))
    {
      data[id]=ch;
      id++;   
    }
    // Get field 3 (CRC)
    if ((field==3) && (ch!=0x20))
    {
      crc=ch;
      label[il]='\0';
      data[id]='\0';   
    }
    // First field after 0x0A
    if (ch==0x0A)
    {
      field=1;
      il=0;
      id=0;
    }
    // Each 0x20 is a separator for a new field
    if(ch==0x20) field++;
  }while (ch!=0x03);
   return('\0');
}


I think this will be better handled like this. I do not use gets anymore.
Hope it is the right way.

Br,
Denis
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Mon May 03, 2010 1:55 pm     Reply with quote
Be careful, the first iteration of the loop has the variables 'field', 'il' and 'id' not initialised. This can lead to data loss and/or memory corruption by writing out of array bounds.
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