Strange HSEROUT behaviour

[Charles Linquis]

If I use HSEROUT near the end of a program, and follow it closely with an "END" statement, the output gets truncated. Sometimes it doesn't display at all.

Since the USART only contains two possible bytes - one in the TXReg and one in the send buffer, I would think that at most two bytes would be "chopped off". But instead, sometimes whole lines fail to display. Does anyone know why this happens?

Another HSEROUT issue (possibly related): When I have a timer interrupt running
(a pure assembler routine) and an interrupt occurs, it crashes the HSEROUT string. In the ISR, I save and restore STATUS,W,BSR and FSR. All the other changed variables are local. Is there some software timing loop hidden within the HSEROUT routine, or is something else going on? Are there other registers that I should save and restore?

[Christopher4187]

I experienced something similiar but not sure if it is the same issue as yours. I found that I needed to put a pause statement of 20 milliseconds right after the HSEROUT. I am using this wirelessly and I thought this was the reason. I'm just curious, can you try different pause lengths right after the HSEROUT and let me know what you see?

Chris

[Charles Linquis]

Putting in a PAUSE that is as long as the time it takes to send the string does cure the problem, but my goal is to really understand what PBP is doing.
I have what may be the "worlds largest PBP Program" (My 8722 is nearly full), and now I'm adding SNMP protocol and another layer of interrupts (assembler). I'm noticing some weird behavior, and I'm trying to understand what is going on.

[Bruce]

END places the PIC in a tight loop executing SLEEP continuously.

With HSEROUT, PBP loads the outbound character, then issues a call to the
HSEROUT sub-routine. It doesn't wait for the last character to be sent.

Program execution returns to the next statement right after the call to
HSEROUT, lands on SLEEP, kills the CPU clock, and your last character is
never sent.

Here's how it works;

    DEFINE OSC 4

    HSEROUT ["AB"]
    
    END

Which produces this in assembler;

 0000                GOTO INIT              
   0001  HSEROUT       CLRWDT                 
   0002                BTFSS PIR1, 0x4        
   0003                GOTO HSEROUT           
   0004                MOVWF TXREG            
   0005                BSF STATUS, 0          
   0006                GOTO DONE              
   0007  DONE          BCF STATUS, 0x7        
   0008                BCF STATUS, 0x6        
   0009                BCF STATUS, 0x5        
   000A                CLRWDT                 
   000B  DONERET       RETURN                 
   000C  INIT          BSF STATUS, 0x5        
   000D                MOVLW 0x19             
   000E                MOVWF TXREG            
   000F                MOVLW 0x20             
   0010                MOVWF RCSTA            
   0011                BCF STATUS, 0x5        
   0012                MOVLW 0x90             
   0013                MOVWF RCSTA            
   0014  MAIN          MOVLW 0x41 ; <-- load 1st character      
   0015                CLRF PCLATH            
   0016                CALL HSEROUT ; <-- send it
   0017                MOVLW 0x42    ; load 2nd character
   0018                CLRF PCLATH            
   0019                CALL HSEROUT ; <-- send 2nd character
   001A                SLEEP <-- goes to sleep before 2nd character is sent

The PIC is executing instructions a lot faster than your 8-bit serial data can
be shifted out, so it returns and lands on the SLEEP instruction long before
data can be sent.

You need a pause after HSEROUT for a period of at least 1/baud rate*10 or
loop until the TX buffer flag indicates the last char has been sent.

[Charles Linquis]

Thanks, Bruce!
That is exactly the type of explanation that I was looking for.

Going back to my original question, I find that my ISR "kills" HSEROUT.
Is there some reason why this would happen?

As I mentioned, I'm saving and restoring W,STATUS,BSR, and FSR.

[Bruce]

What's causing it to crash could be several things, but it's impossible to tell
without seeing all of your code.

How often are your interrupts? What happens in your interrupt handler?

[mister_e]

what happen if...

Disable
HSEROUT ["Your String"]
WHILE TXREG : WEND
Enable
END

Now how about

HSEROUT ["YourString"]
WHILE TXREG : WEND
end

[Charles Linquis]

This is on a 1 millisecond interrupt. Chip is 18F8722

Here is a portion of the code...


Asm
IntHandler

movwf wsave
swapf STATUS,W
clrf STATUS
movwf ssave
movf PCLATH,W
movwf psave
movf FSR0,W
movwf fsave

movlw 0xEC ; Reload TMR0 with 65535 - 5000
movwf TMR0H
movlw 0x77
movwf TMR0L

btfsc PIR1,5
goto KeyHit

bcf INTCON,2 ; Clear the interrupt flag

infsnz _MasterClock
incf _MasterClock + 1

movlw 0x03
cpfseq _MasterClock + 1
goto FanRoutine
movlw 0xE8
cpfseq _MasterClock
goto FanRoutine
clrf _MasterClock
clrf _MasterClock + 1


bsf _TPE
goto DoneForNow


FanRoutine

movf PORTB,0,0
movwf _Temp,0
xorwf _OldPortB,0,0
movwf _changedB,0
movff _Temp,_OldPortB


Fan1
btfss _changedB,0
goto DoneForNow
infsnz _Fan1Counter
incf _Fan1Counter+1



KeyHit
bsf _KeyHitFlag
bcf PIR1,5

DoneForNow

movf psave,W
movwf PCLATH
movf fsave,W
movwf FSR0
swapf ssave, W
movwf STATUS
swapf wsave, F
swapf wsave, W
bsf INTCON,7 ; Turn Global interrupts on
bsf INTCON,6 ; Turn Peripheral Interrupts on
retfie ; Return from the interrupt

EndAsm

[Bruce]

I suspect it's your int handler.

btfsc PIR1,5
goto KeyHit ; <-- you never reset timer0 int flag before exiting

bcf INTCON,2 ; (skips over this) Clear the interrupt flag

That may be a problem once retfie re-enables global interrupts.

And if you have your USART receive interrupt enabled, you're not clearing the
receive interrupt with BCF PIR1,5. You have to read whatever is in the USART
receive buffer to clear this flag bit.

Have a look at the 18F series interrupt handler in this example;
http://www.microengineeringlabs.com/...p/serbufAx.bas

[Charles Linquis]

That link sends me to a 16F interrupt handler. Will the same code work on an 18F part?

While I was visiting the MELABS site, I noticed an 18F452 interrupt routine for the timer.

They only saved/restored "W" and "STATUS".
In the 18F series, do I not have to worry about any other registers if I'm not explicity changing them?

[Bruce]

Sorry. Try this one;
http://www.microengineeringlabs.com/...8F/serA452.bas

Normally you'll only need to save FSR0L, FSR0H, WREG and STATUS.