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morind79
Joined: 11 Apr 2008
Posts: 2
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| Help on RS232 and string |
 Posted: Sun May 02, 2010 10:55 am |
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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 ,
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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]);
}
}
}
}
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I am prety sure the code is not correct (pointer...)
If you have some advices :-)
Thanks
Denis |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sun May 02, 2010 4:13 pm |
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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? |
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morind79
Joined: 11 Apr 2008
Posts: 2
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| Posted: Mon May 03, 2010 1:26 am |
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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');
}
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I think this will be better handled like this. I do not use gets anymore.
Hope it is the right way.
Br,
Denis |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Mon May 03, 2010 1:55 pm |
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| 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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