Fast Loop in PICBASIC Pro

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  1. - 17th December 2006, 20:55 #1
    mister_e's Avatar
    mister_e
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    Why not using the internal PWM module instead? it will run in background and you don't need to care about latency etc etc.

    use something like this...
    Code:
    DEFINE OSC 20
TRISC=0
duty var word
duty = 250                                  ' duty value for 50% duty cycle
PR2 = 124                                   ' period for 40KHZ
T2CON = %00000100                           ' timer2 on, prescale 1:1
CCPR1L = duty>>2                            ' eight MSB of duty cycle value
CCP1CON = (duty.lowbyte&3)<<5 | %00001100   ' store  2 LSB of duty 
                                            '  & set PWM mode

START:
      PAUSE 1
      GOTO START
    and look what happen on PORTC.2 pin.

    Need to start it and stop it ? here's something using PORTB.0 as trigger source
    Code:
    DEFINE OSC 20
TRISC=0
duty        var word
PWMMode     var byte
StartStop   var bit

duty = 250                                  ' duty value for 50% duty cycle
PR2 = 124                                   ' period for 40KHZ
T2CON = %00000100                           ' timer2 on, prescale 1:1
CCPR1L = duty>>2                            ' eight MSB of duty cycle value
PWMMode = (duty.lowbyte&3)<<5 | %00001100   ' store  2 LSB of duty 
                                            '    & set PWM mode

START:
    IF PORTB.0=0 then            ' 
        startstop=startstop ^ 1  ' toggle between start/stop
        if startstop=1 then      '
            CCP1CON=PWMMODE      ' Start PWM
            ELSE                 '
                CCP1CON=0        ' Stop PWM
                PORTC.2=0        ' make sure the pin is low   
            ENDIF                '
        WHILE PORTB.0=0 : WEND   ' wait until trigger release
        PAUSE 100                ' debounce delay 
        ENDIF
    GOTO START
    How to calculate those value easy? PicMultiCalc software available bellow for FREE
    http://mister-e.org/pages/utilitiespag.html

    ScreenShot
    <img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1280&stc=1&d=116639098 4">
    HTH
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    Last edited by mister_e; - 17th December 2006 at 21:33.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.
  2. - 18th December 2006, 04:24 #2
    paul borgmeier's Avatar
    paul borgmeier
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    I agree with Steve (and everyone else) that the hardware PWM sounds best for what you described. But, if it will not work for you consider "unrolling" your loops like that shown below. You lose no time in looping but it does cost you more code space (16 repeats is not huge considering the amount of memory in the 877A).
    Code:
    DEFINE OSC 20
TRISB.0 = 0
PORTB = 0

PORTB.0 = 1   ' I = 1 (on for 12.6 uS)
@ nop
Pauseus 12
PORTB.0 = 0   ' (off for 12.4 uS)     
PAUSEUS 12

PORTB.0 = 1   ' I = 2
@ nop
Pauseus 12
PORTB.0 = 0     
PAUSEUS 12

;(more of the same here)

PORTB.0 = 1   ' I = 16
@ nop
Pauseus 12
PORTB.0 = 0     
PAUSEUS 12

Endhere:
goto Endhere
END
    Paul Borgmeier
    Salt Lake City, UT
    USA
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  3. - 18th December 2006, 04:33 #3
    mister_e's Avatar
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    could be...
    Code:
    DEFINE OSC 20
TRISB.0 = 0
PORTB = 0
pauseus 0 ' do nothing good but include PAUSEUS?C macro
TRISB.0 = 0
PORTB = 0
start:
asm
    CHK?RP PORTB
    local a=0
    while a<16        
        BSF PORTB,0
        nop
        PAUSEUS?C 12
        BCF PORTB,0
        nop
        PAUSEUS?C 12
a+=1
    endw
endasm
pause 100
goto start
    now play with the a < x value, and look what happen to your code size.. interesting eh?

    Now compare the code size of
    Code:
    PORTB.0 = 1   
@ nop
Pauseus 12
PORTB.0 = 0     
@ nop
PAUSEUS 12
    copy and pasted 16 times, with the one generated with my solution... mmm interesting

    Sometime MPASM directive are really handy!

    EDIT: you could also use
    Code:
    @   local a=0
@   while a<16
        PORTB.0=1
        @ nop
        PAUSEUS 12
        PORTB.0=0
        @ nop
        PAUSEUS 12
@a+=1
@       endw
    If you don't like the PAUSE?C, BSF, BCF option... both generate the same code.
    Last edited by mister_e; - 18th December 2006 at 05:03.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.
  4. - 18th December 2006, 05:07 #4
    paul borgmeier's Avatar
    paul borgmeier
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    Steve, I did compare code space

    171 for 16X of my block (MPASM)

    211 for your code as posted
    191 (with the second nop removed from yours - which makes T = 25 uS)

    it is interesting.

    Now, the question for me is how the ASM while directive checks without adding time???

    EDIT (after looking up while) - I see .... it doesn't check .... now I understand your comment about code space and it is a handy directive :-) THANKS
    Last edited by paul borgmeier; - 18th December 2006 at 05:12.
    Paul Borgmeier
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  5. - 18th December 2006, 05:13 #5
    mister_e's Avatar
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    MIIP, there's something weird... if i use a 16F877 and this....
    Code:
    DEFINE OSC 20
DEFINE LOADER_USED 1
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_SPBRG 129 ' 9600 Baud @ 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically


pauseus 0
TRISB.0 = 0
PORTB = 0
start:
asm
    CHK?RP PORTB
    local a=0
    while a<16        
        BSF PORTB,0
        nop
        PAUSEUS?C 12
        BCF PORTB,0
        nop
        PAUSEUS?C 12
a+=1
    endw
endasm

pause 100
goto start
    it compile 207 Word

    if i use...
    Code:
    DEFINE OSC 20
DEFINE LOADER_USED 1
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_SPBRG 129 ' 9600 Baud @ 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically


pauseus 0
TRISB.0 = 0
PORTB = 0
start:
    ' #1
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #2
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #3
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #4
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #5
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #6
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #7
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #8
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #9
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #10
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #11
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #12
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #13
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #14
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #15
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

    ' #16
    PORTB.0 = 1   
    @ nop
    Pauseus 12
    PORTB.0 = 0     
    @ nop
    PAUSEUS 12

pause 100
goto start
    Still 207 words...

    EDIT: OK DUDE we hit the button at the same time or...so.
    Last edited by mister_e; - 18th December 2006 at 05:19.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.
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