Using an Assmbly Routine in PBP

[alanmcf]

Hi--

I'm trying to adapt Microchip's AN1076 appnote on DMX to use as an assembly language subroutine in PBP. I'm using a PIC18F4520, 16MHz resonator, PBP 2.5a. What the code should do is initialize the LCD, read the DMX data stream, and then display the value present on DMX channel 7 on the LCD. I am feeding in a DMX signal, and I've had a PBP-coded subroutine working just fine on my hardware test board, but I need more speed. Both the SetupSerial subroutine and the DMXloop subroutine compile just fine, but when I call the DMXloop subroutine, that's the last I see of my program's execution, nothing else happens. I assume I'm jumping off into oblivion somehow... my understanding of assembly is limited, so I'd appreciate any commentary.

Thanks in advance--

--Alan

    ' for PIC18F4530
	DEFINE OSC 16   
	INCLUDE "modedefs.bas"
	include "LCD_defines602.pbp"
	  
'  ****************************************
'  SETUP 
'  ****************************************	
	
	PORTA = %00000000
	PORTB = %00000000
	PORTC = %00000000
	PORTD = %00000000
    trisa = %11111101
    trisb = %01111111
    TRISC = %11101000
    trisd = %11001011
	
	ADCON1 = %00001111					'port a is all digital IO
	CMCON = 7                           'and turn off those pesky comparators
	RBPUx			VAR	INTCON2.7	    'port b pull-ups 1 = disabled 0 = enabled
	RBPUx = 0
	trise.4 =%0                         'disable PSP port
    	
' ===================================
' define hardware pins:
' ===================================
	
	BKLT            var portd.5         'LCD backlight
    
' ================================	
'	define constants & variables:
' ================================

    DMXrxbuffer     var byte[512]
    CountH          var byte
    CountL          var byte
    count0          var byte

    
'  ****************************************
'  INITIALIZATION
'  ****************************************
init:
        call SetupSerial    'set up USART and clear DMXrxbuffer
        
'  ****************************************
'  MAIN LOOP
'  ****************************************

begin:	low bklt                        'turn on backlight
        pause 125                       'pause to let LCD initialize
        lcdout $fe,1                    'clear screen        
        LCDout "  test routine   "       'display splashscreen
        lcdout $fe,$c0,"S/W Version 6xxx"
        pause 1200


low bklt

mainloop:


    Call DMXloop
    lcdout $fe,1
    pause 3
    lcdout dec DMXrxbuffer[7]
    pause 300
    
goto mainloop


asm

_DMXloop
	
; first loop, synchronizing with the transmitter
_WaitBreak
	btfsc	PIR1,RCIF           ; if a byte is received correctly
	movf	RCREG,W             ; discard it
	btfss	RCSTA,FERR			; else 
	bra		_WaitBreak          ; continue waiting until a frame error is detected
	movf	RCREG,W				; read the Receive buffer to clear the error condition

; second loop, waiting for the START code
_WaitForStart
	btfss	PIR1,RCIF			; wait until a byte is correctly received
	bra		_WaitForStart
	btfsc	RCSTA,FERR
	bra		_WaitForStart
	movf	RCREG,W	

; check for the START code value, if it is not 0, ignore the rest of the frame
    andlw   0xff
    bnz     _DMXloop             ; ignore the rest of the frame if not zero 

; init receive counter and buffer pointer        
    clrf    _CountL
    clrf    _CountH
    lfsr    0,_DMXrxbuffer

; third loop, receiving 512 bytes of data
_WaitForData
    btfsc   RCSTA,FERR          ; if a new framing error is detected (error or short frame)
    bra     _RXend              ; the rest of the frame is ignored and a new synchronization
    							; is attempted

	btfss	PIR1,RCIF			; wait until a byte is correctly received
	bra		_WaitForData	    ;
	movf	RCREG,W				; 

_MoveData
	movwf	POSTINC0			; move the received data to the buffer 
                                ; (auto-incrementing pointer)
	incf	_CountL,F           ; increment 16-bit counter
	btfss	STATUS,C
	bra		_WaitForData
	incf	_CountH,F

	btfss	_CountH,1            ; check if 512 bytes of data received
	bra		_WaitForData

_RXend	
	return

;****************************************************************

; Setup Serial port and buffers
_SetupSerial

;Clear the receive buffer
	lfsr	0,_DMXrxbuffer
_CBloop
	clrf	POSTINC0	    ; clear INDF register then increment pointer
	incf	_CountL,F
	btfss	STATUS,C
	bra		_CBloop
	incf	_CountH,F

	btfss	_CountH,1
	bra		_CBloop	

; Setup EUSART
	bsf		TRISC,7         ; allow the EUSART RX to control pin RC7
	bsf		TRISC,6         ; allow the EUSART TX to control pin RC6

	movlw	0x04			; Disable transmission
	movwf	TXSTA			; enable transmission and CLEAR high baud rate

	movlw	0x90
	movwf	RCSTA			; enable serial port and reception

	bsf		BAUDCON,BRG16	; Enable UART for 16-bit Asyn operation
	clrf	SPBRGH

	movlw	.15				; Baud rate is 250KHz for 16MHz Osc. freq.
	movwf	SPBRG	

	return

endasm