Receiving Packet Array In Usart

[crhomberg]

The value of SPBRG at 64 works fine when I tested byte by byte.

My serout2 on PORTA.0 is working fine and the loop is looping (led toggling).
The problem is that as I send data packets to the input it immediatley gets a buffer overrun error.

Regards


Chris

[skimask]

The problem is that as I send data packets to the input it immediatley gets a buffer overrun error.

Which input? The PICs input, PC's input, camera's input...

[crhomberg]

I used to receive the packets using SERIN2 and it works quite well but when the data comes one after another too fast I start loosing packets while the program is out doing other things after the serin2 times out.


'*************** Variables for Receiving Pelco-P data *********

data_1 VAR BYTE ' Header
data_2 VAR BYTE ' ID Camera
data_3 VAR BYTE ' 1st Data
data_4 VAR BYTE ' 2nd Data
data_5 VAR BYTE ' 3th DAta
data_6 VAR BYTE ' 4th DAta
data_7 VAR BYTE ' Trailer
data_8 VAR BYTE ' Checksum

'*************** CONSTANTS ***********************
baud con 16390'Baud rate for test pin output



START:


'**RECEIVE DATA FROM RS485 AND SEE IF IT IS A PELCO-P COMMAND ****

Receiving:


SERin2 DATAIN,188,1000,timeout,[data_1,data_2,data_3,data_4,data_5,data_6,data_7,d ata_8]

timeout:

if (data_1 <> $A0) then 'Check if the 1st byte is Pelco ($A0).
goto receiving
endif

etc.... etc do the decoding....

[crhomberg]

I have my PIC receiving data from a camera PTZ control console using RS485 which sends out data every time I move the joystick telling the PIC what to do. I have a RS485 to TTL converter on the input of the PIC

Regards

Chris

[skimask]

Send out bytes using serout one byte at a time instead of a whole string of bytes and in between sending out bytes, do a quick serin check to see if anything is there.

[crhomberg]

I don't have a choice, the data always comes in groups of 8.
The serout is just for debugging, not really needed finally.
I must be able to read in 8 bytes and then check if the 1st one is $A0 and the 7th $AF. When that is true I can use the data. The packets come at 4800bps and in bursts relatively far apart (That is how I got away with serin2 until now, it just lost packets from time to time)
I need to stop what the program is doing when that 1st byte arrives and then channel in the next 7 into an array or sepparate vars.

Regards

Chris

[sougata]

Hi,

I have done an application where a PIC 18F452 is connected in parallel with a dumb terminal. It parses incoming strings on the fly in an asm based INT routine and keeps required data in specified variables.For your app @4800 try this.

1. Set up a ring buffer.
2. Within the interrupt hunt for the trailer, if found set a flag.
3. Jump back to the header location to find if it was a complete command set.
4. Verify Checksum
Then you now where your data of interest are and handle them in the main routine.

[skimask]

I don't have a choice, the data always comes in groups of 8. The serout is just for debugging, not really needed finally. I must be able to read in 8 bytes and then check if the 1st one is $A0 and the 7th $AF. When that is true I can use the data. The packets come at 4800bps and in bursts relatively far apart (That is how I got away with serin2 until now, it just lost packets from time to time) I need to stop what the program is doing when that 1st byte arrives and then channel in the next 7 into an array or sepparate vars.
Regards
Chris

Put that input on portB and use the 'interrupt on change' feature...
I.E. - you're transmitting, something starts coming in on the serial line. Stop transmitting immediately and start receiving.

What you're trying to do isn't impossible. It's just getting past the PicBasicPro serial commands and using straight hardware and interrupts to handle it in the 'background'.
I suggest playing around with interrupts first, doesn't matter which one, just play with them. Then work your way up to using the serial port, both RX and TX, use some sort of buffering setup.

[crhomberg]

I don't understand how to setup a ring buffer, is this in the main program?
How does a ring buffer work?
Is this using asm interrupts or ON INT?

[Darrel Taylor]

Chris,

You already have a buffer, it doesn't need to be a "ring".
But it does need to work properly.

In your original routine...

'******************* interrupt routine *********************
disable

myroutine:
if PIR1.5=1 then
    PELCO[BYTECOUNT]=RCREG
    IF RCREG=$AF THEN
        GOSUB SENDATA
        PIR1.5=0
    ELSE
        BYTECOUNT=BYTECOUNT+1
        GOTO MYROUTINE
    ENDIF
ENDIF
        
resume
enable

When testing the value of RCREG, it also removes a byte from the USARTs buffer (if one's available).

And, there's currently no way to reset BYTECOUNT, it just keeps counting, which then overwrites memory areas that you don't want it to.

Try this...

'******************* interrupt routine *********************
disable

myroutine:
if PIR1.5=1 then
    temp = RCREG
    if temp = $A0 then BYTECOUNT = 0
    if BYTECOUNT < 8 then    
        PELCO[BYTECOUNT]=temp
        BYTECOUNT=BYTECOUNT+1
        IF (BYTECOUNT = 8) and (temp=$AF) THEN GOSUB SENDATA
        GOTO MYROUTINE
    ENDIF
ENDIF
        
resume
enable

HTH,