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UART too fast stops everything

 
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theteaman



Joined: 04 Aug 2006
Posts: 98

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UART too fast stops everything
PostPosted: Thu Aug 31, 2006 8:08 am     Reply with quote

Hi there

When I send data at fast rates from my PC uart to the PIC uart, the PIC crashes. The reason I know the PIC crashes is because I always leave one of the PIC IO pins powering an LED, and at the point of the crash, the LED turns off...

I thought it might be because of a buffer overrun but that wouldnt explain the LED turning off would it? Also I added the 'ERRORS' directive to the use rs232 statement to stop any 'blocking' but that still didn't fix the crash.

My rs232 statement is:
Code:
#use rs232(baud=57600, xmit=PIN_C6, rcv=PIN_C7, PARITY=E)


I know the code is working otherwise because when I introduce a 400ms delay after every 256 or so bytes, there is no crash. Its only when I don't have this delay.. can someone help? thanks
asmallri



Joined: 12 Aug 2004
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PostPosted: Thu Aug 31, 2006 8:32 am     Reply with quote

Assuming you do NOT have the WDT enabled, I would look elsewhere for the problem. Something to do with your ring buffer pointer management.
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theteaman



Joined: 04 Aug 2006
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PostPosted: Thu Aug 31, 2006 8:56 am     Reply with quote

asmallri wrote:
Assuming you do NOT have the WDT enabled, I would look elsewhere for the problem. Something to do with your ring buffer pointer management.


Nah I dont have WDT enabled. My communication works basically like this:
- send 256bytes from PC to PIC
- PC then delays (X ms)
- during this delay the PIC does whatever it has to do

this process is repeated from about 30 * 256bytes.
etc..

For this reason it seems not to be the ring buffer (because I dont have one). The greater the value of X, the less chance of the PIC crashing.. but is crashing a sign of a buffer overflow??
treitmey



Joined: 23 Jan 2004
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PostPosted: Thu Aug 31, 2006 9:20 am     Reply with quote

yes.
Without the errors argument in the #use rs232 an overflow will
stop reception and that will look like the PIC stopped.

Either put in "errors" in the #USE rs232
ie
#use rs232(baud=19200,xmit=PIN_B3,invert,errors,stream=DEBUG)
((((note this isn't a great example because errors param isn't applicable to software serial)))
but the syntax is ok
or

check it/handle it by hand.
16F877
Code:
#bit  RCIF=0x0C.5
#bit  CREN=0x18.4
#bit  OERR=0x18.1
#bit  FERR=0x18.2
#byte RCREG=0x1A
...
    if (OERR){
      bit_set(ERRORS,0);//let someone know overflow happened
      CREN = 0;
      delay_cycles(1);
      CREN = 1;//clear the overflow
    }


theteaman



Joined: 04 Aug 2006
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PostPosted: Thu Aug 31, 2006 5:19 pm     Reply with quote

Thank you, but a blocking UART shouldnt cause all the PIC IO pins to output low should it? - an LED I have lighted suddenly switches off. I tried the errors directive but it still happens Confused
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Thu Aug 31, 2006 5:46 pm     Reply with quote

As always, post a small but complete program that demonstrats the problem.
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Fri Sep 01, 2006 3:09 am     Reply with quote

theteaman wrote:
Thank you, but a blocking UART shouldnt cause all the PIC IO pins to output low should it? - an LED I have lighted suddenly switches off. I tried the errors directive but it still happens Confused
Outputs can only change state when your program is misbehaving and writes data to the output port. The only other possibility I can think of is that the pin is no longer an output but changed to an input, for example by a processor reset.

I don't know how you connected the LED, but are you sure the pin is still an output? If yes, then a LED connected from the positive power supply would light up.

Add some code at program startup to signal you the processor has (re)booted, for example by flashing a LED.
Mark



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Posts: 2838
Location: Atlanta, GA

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PostPosted: Fri Sep 01, 2006 6:18 am     Reply with quote

ckielstra wrote:
theteaman wrote:
Thank you, but a blocking UART shouldnt cause all the PIC IO pins to output low should it? - an LED I have lighted suddenly switches off. I tried the errors directive but it still happens Confused
Outputs can only change state when your program is misbehaving and writes data to the output port. The only other possibility I can think of is that the pin is no longer an output but changed to an input, for example by a processor reset.

I don't know how you connected the LED, but are you sure the pin is still an output? If yes, then a LED connected from the positive power supply would light up.

Add some code at program startup to signal you the processor has (re)booted, for example by flashing a LED.


A reset would make the pin an input again but it should also execute the code which turns on the LED again.
theteaman



Joined: 04 Aug 2006
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PostPosted: Fri Sep 01, 2006 4:59 pm     Reply with quote

Good ideas, thanks. I'll also try to post some code but I need to get it smaller and simple to demonstrate the problem. thanks Smile
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