Funny 'if' routine

[Dakta]

I'm writing a small PIC program in MikroC that will receive sequences of bytes from a serial port and look for patterns.

Because the patterns will be 8 bytes long, I'm using an array on a rolling basis, as a buffer - first in, first out style. The serial reception is handled by an interrupt.

I've tested the receiving and sending, if I program it to return all bytes to me, it works perfectly. The problem I'm having is that it is not correctly identifying the patterns that I am looking for.

Here's the 'test' stage code:

void interrupt() { //Serial Data Received
 
 //put received data into buffer
 //shuffle buffer up array
 if (UART1_Data_Ready() == 1) {
 RX_Buffer[0] = RX_Buffer[1];
 RX_Buffer[1] = RX_Buffer[2];
 RX_Buffer[2] = RX_Buffer[3];
 RX_Buffer[3] = RX_Buffer[4];
 RX_Buffer[4] = RX_Buffer[5];
 RX_Buffer[5] = RX_Buffer[6];
 RX_Buffer[6] = RX_Buffer[7];
 RX_Buffer[7] = UART1_Read();
 }

//check for sequences starting with '0' - return 255 if sequence found
if (RX_Buffer[0] == 0) UART1_Write(255);

 }

All that's supposed to happen there is that it will add receiving data to the array (chucking the oldest out) so we have the most recent 8 received bytes. Then it will return '255' to the computer if the sequence (position 0) is equal to 0.

However, this doesn't work - when zero's are sent, more than 8 in a sequence, the 'if' routine never identifies it.

I added the code to make sure the data was being received correctly:

UART1_Write(RX_Buffer[0]);

to the bottom of the interrupt routine, it confirms that the element of the array is containing the value I'm looking for.

It's been a while since I used C so I'm a little rusty, but I can't work out what's wrong with my 'if'. Any ideas?

 

[Dakta]

I beleive I 'may' have solved the problem.

I beleive the problem is a bug in the simulation tool i'm using as I tried programming the device and did not seem to be able to replicate the error

 

[Robin2]

Rather than shuffle the array contents I suggest you use a variable to index into the array (probably 2 variables - one for reading and one for writing) and increment the variable so that at all times you read the array with abc = RX_BUFFER[read_posn] and write to the array with RX_BUFFER[write_posn] = incoming_value. Then increment the _posn variables and set them back to 0 when you get to the end of the array.

 

[Dakta]

Thanks for the suggestion, are there technical reasons why that would be superior or would it just be more simple/managable?

 

[Robin2]

I was mainly thinking of it being simpler but it may also be faster. Also it is a technique that may be appropriate in other circumstances.