another state machine example

[richard]

on the other forum this was asked

I'd like to create a millisecond counter with a range from 5 milliseconds to 40 milliseconds. It does not have to be resolved to a single millisecond; e.g. need to know when it's hit each in a series of N+5 (5,10,15,20,25,30,35,40) milliseconds known. There'll be a photo interrupter reading an aperture in a disk and possibly be 8 LEDs each designating those 8 positions. Sort of like how an LED guitar tuner displays; 1st LED=5ms, 2nd=10ms, 3rd=15ms, etc.
Will I need a subroutine to avoid inaccuracy? Can I get by with PULSIN?

http://support.melabs.com/forum/picb...unter#post8333

no complete code solution was asked for. seemed a waste so i will post my idea here as an example of a state machine solution rather than waste the effort
the asm code is a leftover of first implementing a full charlieplexer for the leds , until i realized there was never a need to show more than one at any one time
and cut it down to a charlie with no plexer

 ;@ 12f1822#CONFIG
  __config _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_ON & _CLKOUTEN_OFF & _IESO_ON & _FCMEN_ON
  __config _CONFIG2, _WRT_OFF & _PLLEN_OFF & _STVREN_ON & _BORV_19 & _LVP_OFF
#ENDCONFIG




goto overasm 
asm
pc_val           ;led charlieplex lata data 
    addwf   PCL, F                   
    retlw 	2       
    retlw 	1             	
    retlw 	1   
    retlw 	4
    retlw 	1
    retlw 	32                         
    retlw 	2  
    retlw 	4
    retlw 	2
tc_val             ;led charlieplex trisa data 
    addwf   PCL, F           
    retlw 252
    retlw 252
    retlw 250
    retlw 250
    retlw 222 
    retlw 222 
    retlw 249
    retlw 249
    retlw 221
_LDS     ;SHOW LED  X=1 TO 9
    BANKSEL LATA       ;start with all LEDS  off
    clrf LATA
    BANKSEL TRISA
    movlw 0xff
    IORWF TRISA,F
    BANKSEL 0
    decf _ledx ,w          
    L?CALL  tc_val      ;lookup tris value
    BANKSEL TRISA
    MOVWF  TRISA
    BANKSEL  _ledx
    decf _ledx,W
    L?CALL  pc_val      ;lookup port value
    BANKSEL LATA               
    MOVWF  LATA         ;ignite the led
    BANKSEL 0  
    RETURN 
 endasm
overasm:


DEFINE OSC 16
OSCCON = $78
ANSELA = 0


TRIGGER  VAR       PORTa.4    ;timer gate control pin
timer    var word  ext        ;the result in uS
ledx     var byte  bank0      ;current led to ignite   1-9
tmp      var word             ;temporary store 
state    VAR BYTE             ;current state of machine  0, uninitialised  1, seeking pulse  2, pulse detected  3, good result 4, error
old_state VAR BYTE            ;previous state of machine 
@timer = TMR1L                ;alias tmr1 to timer var
clear


'post
FOR  ledx= 1 TO 9
    CALL LDS     ;SHOW LEDx  
    pause 80
NEXT


IOCAN.4 = 1      ;SET FALLING EDGE DETECTION INT ON TRIGGER PIN 
T1CON   = $20    ;timer off
T1GCON  = $c0    ;timer gate control to count on high gate
state   = 1      ;all done lets go


MAIN:
    if state != old_state then        ;manage state change
        if state == 1 then            'reset timer
            pir1.0 = 0
            TIMER = 0
            T1CON.0 = 1
            ledx= 9           ;led 9 on
            CALL LDS
            IOCAF=0
        elseif state == 2   then      ;evaluate result
            if pir1.0 then    ;timer overflow
                ledx= 4       ;led overflow on
                state = 4                     
            elseif timer < 4800 then  ;too short
                ledx= 8       ;led UNDER on
                state = 4 
            elseif timer > 40200 then ;too long
                ledx= 1       ;led OVER on
                state = 4 
            else                      ;goldilocks
                TMP = TIMER / 5000 - 1
                IF TIMER // 5000 > 2499 THEN TMP = TMP + 1    ;round up
                ledx= 8 - TMP ;led ledx on
                state = 3 
            endif
            CALL LDS      ;SHOW LEDx
            TMP=1500        ;15 sec timeout to show result then reset
        endif
        old_state = state      
    endif
    select case state     ;manage current state  
        case  1           ;SEEKING A PULSE CAPTURE EVENT
            IF IOCAF.4 || pir1.0   THEN    ;FALLING  EDGE ON TRIGGER PIN DETECTED or overflow
                T1CON.0 = 0     ;stop timer no retriggering
                LATA = 0        'led9 oFF show pulse captured
                state = 2 
            endif
        case  3           ;good result show it
            if tmp then           ;15 sec timeout then reset
                TMP = TMP - 1     
            else
                state = 1         ;then reset
            endif  
        case  4           ;error condition flash ledx
            if tmp then           ;15 sec timeout countdown then reset
                if tmp//50==0 then LATA = 0    
                if tmp//50==25 then CALL LDS  
                TMP = TMP - 1     
            else
                state = 1         ;then reset
            endif     
    end select 
          PAUSE   10       ;set loop to 10 mS 
GOTO   MAIN