Capture and compare serial data

[Dennis]

Hi Guys

Haven't been around in a while and I hope everyone is well :-)

I am trying to do a kind of wireless capture and compare but I have a problem on the receiving end that I lookings for some suggestions on.

Heres the pseudo code:
1.send/transmit 4 bytes 4 times (done and it's working!)

2.receive the 4 bytes 4 times (the receiver receives the 4 bytes 4 times successfully -using serial port tool)

3.Store the 4 instances/lines of 4 bytes (Here's where I have the problem)

4.Compare lines 3 and 4 (or any of the lines with one of the others.This is the other problem I have)

Heres my code:

        
'Variables begin here
	SYNK    VAR BYTE
    	SYNK = $7E   '126 DECIMAL, BINARY 11111110
    	TRAIN   VAR BYTE
    	TRAIN =  $B3
    	WNUM    VAR BYTE
    	XNUM    VAR BYTE
    	YNUM    VAR BYTE
    	ZNUM    VAR BYTE
    	WNUM = 31
    	XNUM = 1
    	YNUM = 2
    	znum = 2
'end of variables

main:
	low led 'set led low
        If GPIO.2 = 1 then main 'check button
        
send:             
          
          for counter = 0 to 3
     
            DEBUG train,train,train,train,train,synk,WNUM,XNUM,YNUM,ZNUM,$d,$a
     	
           next counter
              high led 'set led high
        
             pause 200
    goto main
end

So as you can see I use DEBUG to send the same this to the serial port 4 times which renders this output in the serial tool:

³³³³³~
³³³³³~
³³³³³~
³³³³³~

which converted to DECIMAL looks like this:

17917917917917912631122
17917917917917912631122
17917917917917912631122
17917917917917912631122

PERFECT but .....

How can I receive and store each instance of WNUM,XNUM,YNUM,ZNUM.

In other words I would like to have four instances of WNUM,XNUM,YNUM,ZNUM, so I could compare each instance of WNUM,XNUM,YNUM and ZNUM.

What is the best way to do it ?

Would I use 4 different arrays?
For example array1 would hold the first line conatining the values for WNUM,XNUM,YNUM,ZNUM.
Array2 would hold the values for the second line and array3 for line 3 and array4 for line 4.

Some help would really be appreciated.

Kind regards

Dennis

[Dennis]

In my frustration @ myself and my rush to post I really messed up the english for this line

I am trying to do a kind of wireless capture and compare but I have a problem on the receiving end that I lookings for some suggestions on.

What it should read is :
I am trying to do a kind of wireless capture and compare but I have a problem on the receiving end that I am looking for some suggestions on.

Looking forward to your replies

Thanks so much

Dennis

[mackrackit]

Hey Dennis,

An array(s) would be the way to do it. Could compare separate bits or the whole array sorta like doing a checksum. Lots of possibilities.

This may give you some ideas on how to set it up
http://www.picbasic.co.uk/forum/showthread.php?t=544

[Dennis]

Dave :-)

Thanks a million for the tip ...very helpful indeed.
Still bashing around with the options.

Now this is what prompted me to post this thread, if I use an array , should I use a byte or a word array ?
Which would be the better one?
Why choose one over the other?

No matter what type of array I choose, I think the comparison of bytes would become rather cumbersome not so ?

For example if I choose a word array then the first line received would receive the first 4 bytes(0 to 4) WNUM,XNUM,YNUM,ZNUM.
The second line would be held in byte 5 to 7 not so ?

Then to compare each line is where things start to get cumbersome I think and by that I mean lots of IF,THEN statements.
So for example to compare lines 1 (WNUM,XNUM,YNUM and ZNUM and line 2 (WNUM,XNUM,YNUM and ZNUM I might have to do something like :
MyWordArray var WORD [7]
If (MyWordArray.0 and MyWordArray.1 and MyWordArray.2 and MyWordArray.3 ) = (MyWordArray.4 and MyWordArray.5 and MyWordArray.6 and MyWordArray.7) THEN DoSomething

This doesn't look quite right :-(

That's the problem I have ... I am really battling to somehow compare each line.
Is there a way of doing this by sending and receiving everything as a STRING and comparing the entire string ?

Any more suggestions would really be appreciated.

Kind regards

Dennis

[Charles Linquis]

Sometimes, when the strings you have to compare are very long, or when there are a lot of them, rather than compare them byte-for-byte, it is easier to use a good CRC algorithm on each one, then compare the CRCs.

[Dennis]

@Charles and Dave

I definitely agree with the checksum idea , in fact, it is the checksum concept that has led to the confusion

As a reference let's use this thread (thanks Art for his input!)
http://www.picbasic.co.uk/forum/showthread.php?t=12492

SO from that thread POST #2 one possible method of checksumming is described, since it's fairly straight forward we could use that as a reference.

So the bytes I would like to transmit are declared as
WNUM,XNUM,YNUM and ZNUM respectively.

***NOTE that this fairly trivial when comparing each byte of a single transmission BUT I am transmitting the same thing 4 times and that's whats confusing me.
The reason I want to do it 4 (or more) times is because from what I have seen in my tests the first one and/or second received line is usually damaged/corrupted so I figured it is probably best if I compare the third and 4th transmitted lines. Does that make sense?

Here's an example of the transmit code:

WNUM as byte
XNUM as byte
YNUM as byte
ZNUM as byte
CHECKSUM as byte
CHECKSUM = $3F

'now do the XOR checksumming
Checksum = Checksum ^ WNUM
Checksum = Checksum ^ XNUM
Checksum = Checksum ^ YNUM
Checksum = Checksum ^ ZNUM

'and now TX the data 4 times 
main:
	low led 'set led low
        If GPIO.2 = 1 then main 'check button
        
send:             
          
          for counter = 0 to 3
     
   DEBUG train,train,train,train,train,synk,WNUM,XNUM,YNUM,ZNUM,CHECKSUM,$d,$a
     	
           next counter
              high led 'set led high
        
             pause 200
    goto main
end

On the receiver side the code (as per the thread referenced earlier) would look like this:

'Variables begin here 
   
    SYNK    VAR BYTE
    SYNK = $7E
    WNUM    VAR BYTE
    XNUM    VAR BYTE
    YNUM    VAR BYTE
    ZNUM    VAR BYTE
    CHECKSUM var byte 'this holds the received checksum
    CHECKSUM_CHECK var byte 'hold the XOR'd value
    Checksum_Check = $3F 'this is the checksum value to XOR with 
    
  'Variables end here 

DEBUGIN [WAIT(SYNK),WNUM,XNUM,YNUM,ZNUM,CHECKSUM]
           ' wait for SYNK, when received store next 4 bytes in variables WNUM,XNUM,YNUM,ZNUM
           'then send these to hyperterminal or serial program or wherever 
            
            'checksum the received bytes using XOR with 3F 
            Checksum_Check = Checksum_Check ^ WNUM
            debug "xNUM checksum_check is ",HEX checksum_check
            Checksum_Check = Checksum_Check ^ XNUM
            debug "wNUM checksum_check is ",HEX checksum_check
            Checksum_Check = Checksum_Check ^ YNUM
            debug "yNUM checksum_check is ",HEX checksum_check
            Checksum_Check = Checksum_Check ^ ZNUM
            debug "zNUM checksum_check is ",HEX checksum_check
            
IF Checksum_Check = Checksum THEN
DEBUG "WNUM is ",DEC WNUM,"XNUM is ",DEC XNUM,"YNUM is ",DEC YNUM,"ZNUM is ",DEC ZNUM,$d,$a
ENDIF

BUT as you can see the receive code only does its thing for each received line. I want to store all 4 lines of data then do a compare of the received lines 3 and 4.

See the problem is if only one transmission is made (one line) and there is a corruption of a byte (checksum mismatch anywhere in the line) then the TX fails. That is why I thought to send and receive 4 lines (or more) of the same thing and then do a compare.

I am totally confused (again)

PLEASE HELP..........!

Kind regards

Dennis