;   Keith Neufeld
;   25-Mar-2006
;
;   LogoChip program to oscillate 24kHz ultrasonic transducer using
;   PIC PWM output.  Uses PWM channel 1 on port C2.


;------------------------------------------------------------------------------
;   Routines for manipulating CCP1 and timer 2 for PWM.
;------------------------------------------------------------------------------


constants [
    [CCP1CON $fbd]			;   capture/compare/PWM 1 control reg
    [T2CON $fca]			;   timer 2 control register
	[TMR2ON 2]				;   timer 2 enable bit
	[T2CKPS1 1]				;   timer 2 prescale bit 1
	[T2CKPS0 0]				;   timer 2 prescale bit 0
    [CCPR1L $fbe]			;   C/C/P 1 register low byte
    [PR2 $fcb]				;   timer 2 period register

    [pwm-port-ddr portc-ddr]		;   PWM 1 outputs on port C2
    [pwm-bit 2]

    [period 82]				;   timer period to use for 24kHz
]


;   Initialize PWM by configuring timer 2 for PWM period and enabling PWM mode.
to pwm-init
    clearbit pwm-bit pwm-port-ddr	;   set PWM port to output


    ;setbit T2CKPS1 T2CON		;   set timer 2 prescalar to 16 (1x)

    ;clearbit T2CKPS1 T2CON		;   set timer 2 prescalar to 4 (01)
    ;setbit T2CKPS0 T2CON

    clearbit T2CKPS1 T2CON		;   set timer 2 prescalar to 1 (00)
    clearbit T2CKPS0 T2CON


    write PR2 period			;   set timer period for 24kHz
    write CCPR1L (period / 2)		;   set 50% duty cycle

    write CCP1CON 12			;   set PWM mode
end


;   Enable PWM by turning on timer 2.
to pwm-on
    setbit TMR2ON T2CON			;   turn on timer 2
end

;   Disable PWM by shutting off timer 2.
to pwm-off
    write PR2 0				;   disable PWM by setting period to 0
    wait 1
    clearbit TMR2ON T2CON		;   and turn off timer 2
end


;------------------------------------------------------------------------------
;   Routines for manipulating CCP2 and timer 3 for capture.
;------------------------------------------------------------------------------


constants [
    [CCP2CON $fba]			;   capture/compare/PWM 2 control reg
	[CCPxM-CAP-EVERY #0100]			;   capture every falling edge
    [CCPR2H $fbc]			;   CCP 2 register low byte
    [CCPR2L $fbb]			;   CCP 2 register low byte
    [PIR2 $fa1]				;   peripheral interrupt request 2
	[CCP2IF 0]				;   timer 3 interrupt bit
    [CCP2-PORT portc]			;   uses portc pin 1
	[CCP2-BIT 1]
    [CCP2-DDR portc-ddr]

    [T3CON $fb1]			;   timer 3 control register
	[T3CCP2 6]				;   timer 3 CCP mode bit 2
	[T3CCP1 3]				;   timer 3 CCP mode bit 1
							;   1x src CCP1+2
							;   01 src CCP2
	[T3CKPS1 5]				;   timer 3 prescale bit 1
	[T3CKPS0 4]				;   timer 3 prescale bit 0
							;   11 = 1:8
	[TMR3ON 0]				;   timer 3 enable bit
    [TMR3H $fb3]			;   timer 3 high byte
    [TMR3L $fb2]			;   timer 3 low byte
]


;   Initialize CCP by configuring timer 3 and enabling capture mode.
to ccp-init
    write CCP2CON CCPxM-CAP-EVERY	;   config to capture every falling edge

    clearbit T3CCP2 T3CON		;   set T3CCP to 01 to make T3 src CCP2
    setbit T3CCP1 T3CON			;	and T1 src CCP1

    setbit T3CKPS1 T3CON		;   set T3CKPS to 11 to use 1:8
    setbit T3CKPS0 T3CON		;	prescalar

    setbit TMR3ON T3CON			;   enable timer 3

    setbit CCP2-BIT CCP2-DDR		;   set CCP2 (RC1) pin for input
end


;   Record starting value of timer 3 and clear capture flag.
global [ccp-before]
to ccp-start
    setccp-before ((read TMR3H) * 256) + read TMR3L
    clearbit CCP2IF PIR2
end

;   Wait for capture event and return duration.
global [ccp-after]
to ccp-wait
    waituntil [testbit CCP2IF PIR2]	;   wait for capture interrupt
    setccp-after ((read CCPR2H) * 256) + read CCPR2L
    output ccp-after - ccp-before
end


;------------------------------------------------------------------------------
;   Top-level routines to tie it all together.
;------------------------------------------------------------------------------


;   For the sake of testing, activate on powerup.
constants [[standalone 0]]
to powerup
    pwm-init
    ccp-init
    if standalone [ pwm-on ]
end


;   Send a short burst of tone.
to ping
    pwm-on
    mwait 1
    pwm-off
end

;   Ping and measure time to reply.
to range
    ccp-start				;   record start time
    ping
    output ccp-wait			;   wait for echo and return duration
end