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ferkar
Joined: 14 Jul 2007
Posts: 38
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| gets() does not work proper in interrupt!!! |
 Posted: Wed Jul 14, 2010 1:07 am |
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hi everbody,
i am trying to make communicate a 18f452 and PC(visual basic).
at PC side,(by using command button)
mscomm1.output = set+","set2+","+set3+","+";"+chr(13)
at pic side to receive and seperate data(which were seperated by commas)
gets(string); // string[10]
strcpy(term,",;");
ptr = strtok(string, term);
while(ptr!=0) {
receive_buffer(ptr); // *ptr , receive buffer[10]
ptr = strtok(0, term);
i++; // i int8
}
my problem is that:
the above code is working well in main(). however, i would like to get the serial data in interrupt routine. in this case the code works only once or twice.!!!
i did not know how to deal with it.
thanks in advance... |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Wed Jul 14, 2010 1:24 am |
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gets() is waiting for data until the terminating character, it's absolutely unsuitable for interrupt usage.
A reasonable way to achieve what you intend is to write the received serial data to a buffer during interrupt and process the buffer in the main() loop. A ring buffer involving two pointers is the most versatile way. There are geenric examples for buffered UART receive shipped with CCS C, I hope. At least, buffered UART is used with the MODBUS examples. Personally, I use to write it from the scratch, so I don't care much for the examples. |
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ferkar
Joined: 14 Jul 2007
Posts: 38
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| Posted: Wed Jul 14, 2010 1:44 am |
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strtok() command seperate the data
and chr(13) is terminating character.
therefore it should work i think... |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19387
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| Posted: Wed Jul 14, 2010 3:58 am |
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You need to understand a basic point.
The serial interrupt means that _just one_ character is waiting.
gets, waits for an entire string to arrive.
If you call gets, in an interrupt, the code _will_ be hung inside the interrupt, till the whole string arrives.
This has been covered many hundreds of times here in the forum.
ex_sisr.c, shows how to use serial interrupts to store characters into a buffer.
As a sort of 'semi example', I'm posting a set of code (untested - as typed), to put characters into a buffer like ex_sisr, but add the following features:
1) Handle the buffer maths efficiently, if buffer size is not a binary multiple - a fault in ex_sisr.
2) Offer a 'bgetline' function to get a complete CR terminated line from the buffer.
3) Offer a 'line_waiting' test, to say that a CR terminated line has been received.
There are 'caveats' with it, but with care, it should provide a starting point.
| Code: |
////For whatever chip you want....
#include <16f877A.h>
#fuses HS, NOLVP, NOWDT, PUT
#use delay (clock = 20000000)
#use rs232(baud=9600, Bits=8, Parity=N, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
////
//Buffer definitions
#define CR (13)
int8 CR_seen=0;
int1 Overflow=FALSE; //Logic flags for serial handling
#define BUFFER_SIZE 32 //Change this to alter the buffer size
char buffer[BUFFER_SIZE];
int next_in = 0; //Max 255 chars with int here - change if larger needed
int next_out = 0;
#int_rda
void serial_isr(void) {
int temp;
temp=getc();
buffer[next_in]=temp;
if (temp==CR) CR_seen++; //flag if a carriage return
temp=next_in;
if (++next_in==(BUFFER_SIZE)) next_in=0;
if(next_in==next_out) {
next_in=temp; //Buffer overflow
Overflow=TRUE;
}
}
#define bkbhit() (next_in!=next_out) //True is character waiting to be read
#define line_waiting() (CR_seen) //True if _line_ waiting to be read
char bgetc() { //Get single char from buffer - wait if one not ready
char c;
while(!bkbhit()) ;
c=buffer[next_out++];
if (next_out==BUFFER_SIZE) next_out=0;
if ((c==CR)&&(CR_seen>0)) CR_seen--; //If I read a carriage return from buffer
return(c);
}
int1 bgetline(char * str, int MAX) { //Routine to get a line from buffer - returns false if no line...
//MAX is the maximum number of characters to return
int8 ctr;
int8 temp;
MAX--; //make space for null terminator
if (!line_waiting()) {
*str=0; //terminate null string
return 0;
}
for (ctr=0;ctr<MAX;ctr++) {
if ((temp=bgetc())==CR) { //This will give a compiler warning, but is correct.....
*str=0;
return ctr; //Null terminate and exit
}
*(str++)=temp;
}
if (buffer[next_out] == CR) bgetc(); //dump a character if next is CR
*str=0;
return ctr;
} //Returns the number of characters in the 'line'
void main (void) {
int16 dummy;
char line[20];
char chr;
while (TRUE) { //sit looping doing something.....
delay_ms(100);
dummy++;
printf("%ld/n/r",dummy);
//Only use _one_ of the following at a time.
//Now you can test if a character is waiting, and get it like:
if (bkbhit()) chr=bgetc();
//Or wait for a line with:
if (line_waiting()) {
bgetline(line,20);
//here have a line to process
}
//or get a line with:
if (bgetline(line,20)) {
//Here I have a line to process - since bgetline only returns 'true'
//if a line was retrieved.
}
//Now, _caveats_. The code keeps a count of carriage return characters read
//if the buffer overflows, data _will_ be thrown away. If this happens the
//count may become wrong - need to ensure, that either the buffer _is_ big
//enough, or this is handled, by checking the 'overflow' flag....
//Second, the bgetline will return with a line, if the count of characters
//exceeds 'MAX', even if this is not a complete 'line' from the code.
//You need to ensure that the length of the storage is greater than the
//maximum line length you expect (+1), otherwise line parsing will
//become hard.....
}
}
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Best Wishes |
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