Interupt driven servo PWM output


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  1. #1

    Default Interupt driven servo PWM output

    18F46K22 PBP2.6C

    Ok, wanting to command a servo... but, want to use interupts so that the pic can do other things and/or drive multiple servo's...

    So, first of all, i started off doing it with PAUSEUS to make sure i get the timings right...

    Code:
    SERVO1 VAR LATD.0
    SERVO1POS VAR BYTE
    
    MAIN:
    SERVO1POS = 128
    FOR ALOOP = 1 to 250
    SERVO1 = 1
    PAUSEUS 988
    PAUSEUS (SERVO1POS * 4)
    SERVO1 = 0
    PAUSEUS (20000 - (988 + (SERVO1POS * 4)))
    NEXT ALOOP
    
    SERVO1POS = 1
    
    FOR ALOOP = 1 to 250
    SERVO1 = 1
    PAUSEUS 988
    PAUSEUS (SERVO1POS * 4)
    SERVO1 = 0
    PAUSEUS (20000 - (988 + (SERVO1POS * 4)))
    NEXT ALOOP
    
    SERVO1POS = 255
    
    FOR ALOOP = 1 to 250
    SERVO1 = 1
    PAUSEUS 988
    PAUSEUS (SERVO1POS * 4)
    SERVO1 = 0
    PAUSEUS (20000 - (988 + (SERVO1POS * 4)))
    NEXT ALOOP
    GOTO MAIN
    Simples... works perfectly...
    So now i start doing the math and working out the preloads for timers with the help of an excell spreadsheet.

    Code:
    SERVO1 VAR LATD.0
    SERVO1POS VAR BYTE
    PRELOAD1 VAR WORD
    PRELOAD2 VAR WORD
    PRELOAD3 VAR WORD
    SERVOCMDMODE VAR BYTE
    SERVOPWMCOUNTER VAR WORD
    
    PRELOAD1 = 63556                                                                ' 990us   '63556
    TMR0_CON_PL1 CON %10000010                                                      ' 1:8
    PRELOAD2 = 65528                                                                ' 4us     '65528
    TMR0_CON_PL2 CON %10000010                                                      ' 1:8
    PRELOAD3 = 29556                                                                ' 17990us '29556
    TMR0_CON_PL3 CON %10000010                                                      ' 1:8
    
    @ INT_ENABLE TMR0_INT
    TMR0L = PRELOAD3.LOWBYTE
    TMR0H = PRELOAD3.HIGHBYTE
    T0CON = TMR0_CON_PL3
    SERVOCMDMODE = 1
    
    MAIN:
    SERVO1POS = 0
    PAUSE 5000
    SERVO1POS = 128
    PAUSE 5000
    SERVO1POS = 255
    PAUSE 5000
    GOTO MAIN
    
    SERVO_HANDLER:
    IF SERVOCMDMODE = 2 Then
        IF SERVOPWMCOUNTER < 256 THEN
            T0CON = TMR0_CON_PL2
            TMR0L = PRELOAD2.LOWBYTE
            TMR0H = PRELOAD2.HIGHBYTE
            IF SERVO1POS < SERVOPWMCOUNTER THEN
                SERVO1 = 0
                LATD.1 = 0
                LATD.2 = 0
                LATD.3 = 0
            ELSE
                SERVO1 = 1
                LATD.1 = 0
                LATD.2 = 1
                LATD.3 = 0            
            ENDIF
            SERVOPWMCOUNTER = SERVOPWMCOUNTER + 1
        ELSE
            T0CON = TMR0_CON_PL3
            TMR0L = PRELOAD3.LOWBYTE
            TMR0H = PRELOAD3.HIGHBYTE
            SERVO1 = 0
                LATD.1 = 0
                LATD.2 = 0
                LATD.3 = 1
            SERVOCMDMODE = 1
        ENDIF
    @ INT_RETURN
    ENDIF
    
    IF SERVOCMDMODE = 1 Then
        T0CON = TMR0_CON_PL1
        TMR0L = PRELOAD1.LOWBYTE
        TMR0H = PRELOAD1.HIGHBYTE
        SERVOCMDMODE = 2
        SERVO1 = 1
        LATD.1 = 1
        LATD.2 = 0
        LATD.3 = 0
        SERVOPWMCOUNTER = 1
    @ INT_RETURN
    ENDIF
    
    @ INT_RETURN
    And thats where i now have a problem and i don't understand why.
    For debug purposes i added the three LATD outputs so that i could find where i was having issues.

    First off, the frequency is 46.75... ok, i'm sure it can still handle it, and i can adjust this later.
    Secondly, the duty cycle goes from 84.0% to 93.9% to 99.6%...
    It should be 5%, 7.5% and 10%...
    Debug output shows LATD1 at 84.4%...

    LATD1 is for pre-duty phase, when in my code is SERVOCMDMODE = 1
    It's on for 84% of the time and it shouldn't, it should be 5%...

    I'm looking at my code thinking 'that is not possible'...

    So, I've got to have made a stupid mistake somewhere and i can't see it. Can some wonderful person tell me what my stupid mistake is?
    Thanks
    Last edited by comwarrior; - 15th August 2013 at 01:16.

  2. #2

    Default Re: Interupt driven servo PWM output

    Okay, this is worrying... Since no one has said anything that would indicate i havn't make a mistake...
    So the question is why is it not doing what it should...

  3. #3

    Default Re: Interupt driven servo PWM output

    From a quick look at your code. I don't see where your intererupt calls
    "SERVO_HANDLER:". Also the endif's after @ INT_RETURN will never be executed since the program will return before hitting the end if. I can't analysis your code fully but I would restructure it. I did a quick cut and paste on your code. Untested it may get you going

    Code:
    SERVO1 VAR LATD.0
    SERVO1POS VAR BYTE
    PRELOAD1 VAR WORD
    PRELOAD2 VAR WORD
    PRELOAD3 VAR WORD
    SERVOCMDMODE VAR BYTE
    SERVOPWMCOUNTER VAR WORD
    
    PRELOAD1 = 63556                                                                ' 990us   '63556
    TMR0_CON_PL1 CON %10000010                                                      ' 1:8
    PRELOAD2 = 65528                                                                ' 4us     '65528
    TMR0_CON_PL2 CON %10000010                                                      ' 1:8
    PRELOAD3 = 29556                                                                ' 17990us '29556
    TMR0_CON_PL3 CON %10000010                                                      ' 1:8
    SERVOCMDMODE = 1
    '____________________________________________________________
    @ INT_ENABLE TMR0_INT
    TMR0L = PRELOAD3.LOWBYTE
    TMR0H = PRELOAD3.HIGHBYTE
    T0CON = TMR0_CON_PL3
    SERVO_HANDLER:
    IF SERVOCMDMODE = 2 Then
        IF SERVOPWMCOUNTER < 256 THEN
            T0CON = TMR0_CON_PL2
            TMR0L = PRELOAD2.LOWBYTE
            TMR0H = PRELOAD2.HIGHBYTE
            IF SERVO1POS < SERVOPWMCOUNTER THEN
                SERVO1 = 0
                LATD.1 = 0
                LATD.2 = 0
                LATD.3 = 0
            ELSE
                SERVO1 = 1
                LATD.1 = 0
                LATD.2 = 1
                LATD.3 = 0            
            ENDIF
            SERVOPWMCOUNTER = SERVOPWMCOUNTER + 1
        ELSE
            T0CON = TMR0_CON_PL3
            TMR0L = PRELOAD3.LOWBYTE
            TMR0H = PRELOAD3.HIGHBYTE
            SERVO1 = 0
                LATD.1 = 0
                LATD.2 = 0
                LATD.3 = 1
            SERVOCMDMODE = 1
        ENDIF
    
    
    IF SERVOCMDMODE = 1 Then
        T0CON = TMR0_CON_PL1
        TMR0L = PRELOAD1.LOWBYTE
        TMR0H = PRELOAD1.HIGHBYTE
        SERVOCMDMODE = 2
        SERVO1 = 1
        LATD.1 = 1
        LATD.2 = 0
        LATD.3 = 0
        SERVOPWMCOUNTER = 1
    ENDIF
    
    @ INT_RETURN 
    '______________________________________________________________
    MAIN:
    SERVO1POS = 0
    PAUSE 5000
    SERVO1POS = 128
    PAUSE 5000
    SERVO1POS = 255
    PAUSE 5000
    GOTO MAIN
    
    END

  4. #4

    Default Re: Interupt driven servo PWM output

    Mark, Thank you for the reply.
    perhaps i should have explained more.
    I'm using DT's interupts. SERVO_HANDLER is jumped to whenever TMR0 overflows and interrupts.

    The endif's after the @ INT_RETURN do not need to be 'executed' they just define the end if that IF statement. The @ INT_RETURN is placed within the IF statement so that it does not attempt to phrase the second IF statement after executing the first one thus saving time and eliminating a bug.

    MAIN: is their to make the servo move so that i can see it's throw and thus that it's working. Once the PC has setup itself, then it's vars it then needs to fall into the MAIN: loop. Once their it can interrupt into the SERVO_HANDLER when the TMR0 goes off...

    Vars TMR0_CON_PL1 & PRELOAD1 are the TMR0 settings for the 1000us initial on for the control signal to the servo.
    Vars TMR0_CON_PL2 & PRELOAD2 are the TMR0 setting for the PWM duration. This 4us duration is executed 255 times totalling over 1000us for the pwm period of the control signal to the servo.
    Vars TMR0_CON_PL3 & PRELOAD3 are the TMR0 setting for the sleet time after the PWM has finished to make a 50Hz signal (20000us total) to the servo.

  5. #5
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,383

    Default Re: Interupt driven servo PWM output

    Hi,
    I think what Mark is saying is that there are parts of DT-Ints missing in your code, you don't seem to include the needed files and there's no place where you're actually defining/setting up the interrupts. Is that really the complete code you've posted? My guess is no since I don't think it would even compile like that.

    What's your oscillator speed? 8MHz? Do you have that defined somewhere in your code?

    I'm pretty sure that interrupting at 4us intervals isn't going to work, IF you're running at 8MHz that's only 8 instructions between each interrupt and it takes WAY WAY more than that for DT-Ints just to do the context save and restore, the interrupts are "running over them selves".

    /Henrik.

  6. #6

    Default Re: Interupt driven servo PWM output

    ok, here is the full code... i didn't think the top bit was necessary...

    @ __config _CONFIG1H, _FOSC_INTIO67_1H & _PLLCFG_ON_1H & _PRICLKEN_ON_1H & _FCMEN_OFF_1H & _IESO_OFF_1H
    @ __config _CONFIG2L, _PWRTEN_ON_2L & _BOREN_SBORDIS_2L & _BORV_220_2L
    @ __config _CONFIG2H, _WDTEN_OFF_2H & _WDTPS_32768_2H & _CCP2MX_PORTC1_3H & _PBADEN_OFF_3H
    @ __config _CONFIG3H, _CCP3MX_PORTE0_3H & _HFOFST_OFF_3H & _T3CMX_PORTC0_3H & _P2BMX_PORTC0_3H & _MCLRE_INTMCLR_3H
    @ __config _CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _XINST_OFF_4L & _DEBUG_OFF_4L
    @ __config _CONFIG5L, _CP0_OFF_5L & _CP1_OFF_5L & _CP2_OFF_5L & _CP3_OFF_5L & _CP1_OFF_5L & _CP2_OFF_5L & _CP3_OFF_5L
    @ __config _CONFIG5H, _CPB_OFF_5H & _CPD_OFF_5H
    @ __config _CONFIG6L, _WRT0_OFF_6L
    @ __config _CONFIG6H, _WRTC_OFF_6H & _WRTB_OFF_6H & _WRTD_OFF_6H
    @ __config _CONFIG7L, _EBTR0_OFF_7L & _EBTR1_OFF_7L & _EBTR2_OFF_7L & _EBTR3_OFF_7L
    @ __config _CONFIG7H, _EBTRB_OFF_7H

    INCLUDE "DT_INTS-18.bas" ; Base Interrupt System
    INCLUDE "ReEnterPBP-18.bas" ; Include if using PBP interrupts

    ASM
    INT_LIST macro ; IntSource, Label, Type, ResetFlag?
    INT_Handler TMR0_INT, _SERVO_HANDLER, PBP, yes
    endm
    INT_CREATE ; Creates the interrupt processor
    ENDASM

    Define OSC 64 ' Set clock speed

    OSCCON.7 = 0
    OSCCON.6 = 1
    OSCCON.5 = 1
    OSCCON.4 = 1
    OSCCON.1 = 0
    OSCCON.0 = 0
    OSCTUNE.6 = 1

    ANSELA = %00000000
    ANSELB = %00000000
    ANSELC = %00000000
    ANSELD = %00000000
    ANSELE = %00000000

    TRISB = 0
    PORTB = 0
    TRISC = 0
    PORTC = 0
    TRISD = 0
    PORTD = 0
    TRISE = 0
    PORTE = 0
    TRISA = 0
    ALOOP VAR WORD

    SERVO1 VAR LATD.0
    SERVO1POS VAR BYTE
    PRELOAD1 VAR WORD
    PRELOAD2 VAR WORD
    PRELOAD3 VAR WORD
    SERVOCMDMODE VAR BYTE
    SERVOPWMCOUNTER VAR WORD

    PRELOAD1 = 63556 ' 990us '63556
    TMR0_CON_PL1 CON %10000010 ' 1:8
    PRELOAD2 = 65528 ' 4us '65528
    TMR0_CON_PL2 CON %10000010 ' 1:8
    PRELOAD3 = 29556 ' 17990us '29556
    TMR0_CON_PL3 CON %10000010 ' 1:8

    @ INT_ENABLE TMR0_INT
    TMR0L = PRELOAD3.LOWBYTE
    TMR0H = PRELOAD3.HIGHBYTE
    T0CON = TMR0_CON_PL3
    SERVOCMDMODE = 1

    MAIN:
    SERVO1POS = 0
    PAUSE 5000
    SERVO1POS = 128
    PAUSE 5000
    SERVO1POS = 255
    PAUSE 5000
    GOTO MAIN

    SERVO_HANDLER:
    IF SERVOCMDMODE = 2 Then
    IF SERVOPWMCOUNTER < 256 THEN
    T0CON = TMR0_CON_PL2
    TMR0L = PRELOAD2.LOWBYTE
    TMR0H = PRELOAD2.HIGHBYTE
    IF SERVO1POS < SERVOPWMCOUNTER THEN
    SERVO1 = 0
    LATD.1 = 0
    LATD.2 = 0
    LATD.3 = 0
    ELSE
    SERVO1 = 1
    LATD.1 = 0
    LATD.2 = 1
    LATD.3 = 0
    ENDIF
    SERVOPWMCOUNTER = SERVOPWMCOUNTER + 1
    ELSE
    T0CON = TMR0_CON_PL3
    TMR0L = PRELOAD3.LOWBYTE
    TMR0H = PRELOAD3.HIGHBYTE
    SERVO1 = 0
    LATD.1 = 0
    LATD.2 = 0
    LATD.3 = 1
    SERVOCMDMODE = 1
    ENDIF
    @ INT_RETURN
    ENDIF

    IF SERVOCMDMODE = 1 Then
    T0CON = TMR0_CON_PL1
    TMR0L = PRELOAD1.LOWBYTE
    TMR0H = PRELOAD1.HIGHBYTE
    SERVOCMDMODE = 2
    SERVO1 = 1
    LATD.1 = 1
    LATD.2 = 0
    LATD.3 = 0
    SERVOPWMCOUNTER = 1
    @ INT_RETURN
    ENDIF

    @ INT_RETURN

  7. #7
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,383

    Default Re: Interupt driven servo PWM output

    Hi,
    OK, so you're running at 64MHz, that gives it bit more time but I still think that interrupting at 4us intervals is way to fast, there's only 64 instruction cycles between each interrupt and I think it takes more than that for the DT-Ints system just to save and later restore the system variables. And, even if it does work the code would spend most of its time in transit to and from the interrupt handler.

    /Henrik.

  8. #8
    Join Date
    Aug 2013
    Posts
    2

    Post Re: Interupt driven servo PWM output

    The time between transit and interrupt handler is the main culprit here in your servo pulse width modulation. Sometimes the turn around time makes us wait more and it doesn't work in the end even though everything seems right. Happens with me all the time. Connected a lipo battery once as a power supply and it never worked because of misconfiguration.
    Good luck to you.

  9. #9
    Join Date
    Aug 2013
    Posts
    2

    Default Re: Interupt driven servo PWM output

    Quote Originally Posted by LettyLocke View Post
    The time between transit and interrupt handler is the main culprit here in your servo pulse width modulation. Sometimes the turn around time makes us wait more and it doesn't work in the end even though everything seems right. Happens with me all the time. Connected a lipo battery once as a power supply and it never worked because of misconfiguration.
    Good luck to you.
    No more updates regrading the issue? I think the interval time of interrupts must be increased in order for it to work. Interrupt handlers are very tricky to work with.

  10. #10
    Join Date
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    Location
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    Posts
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    Default Re: Interupt driven servo PWM output

    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

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