MicroSeeker PIC/Smalltalk Example

First, here's the Smalltalk code, the method processServo in class PICServoInterface:

	"Process the servo. Basically, servos work using pulse-width
	modulation, where the frequency is about 50 Hz, and the duty
	cycle determines the servo position. The duty cycle should be
	between approximately 1000 and 2000 micro-seconds, although
	different servos may require different duty cylces. These ones
	in particular have a duty cycle between about 690 and 1690 us."

	"Turn on the port to start with, and wait the initial 1 ms."
	ServoPort setBit: Servo1Pin.
	self servoDelay: 195.

	"Now count down, doing a comparison on each interation. When
	the count is equal to the servo's position, turn off the port."

	servoCounter := 250.
		self clearWatchdogTimer.
		servoCounter = servoOnePosition
			ifTrue: [ServoPort clearBit: Servo1Pin]]

				repeatWhile: [servoCounter decrementSkipIfZero].

	ServoPort clearBit: Servo1Pin

And now, the PIC assembler produced:

; ==========================================
; = processServos
; ==========================================
processServos	equ	*
	bsf	ServoPort, Servo1Pin
; Generating call to 'servoDelay:'
	movlw	195
; Pushing WReg (next two instructions)...
	decf	indirectAddressLatch
	movwf	indirect
	call	servoDelay
; Popping (and ignoring) 1 variable from the stack...
	incf	indirectAddressLatch
	movlw	250
	movwf	servoCounter
Label_00	equ	*
	movfw	servoOnePosition, w
	xorwf	servoCounter, w
	btfsc	status, Zero
	bcf	ServoPort, Servo1Pin
	decfsz	servoCounter
	goto	Label_00
	bcf	ServoPort, Servo1Pin

Go back to my PIC/Smalltalk page...