incPID Routine - Help Needed

[Aussie Barry]

Hi Henrik,

All good so far - Step 2 complete.
I have the leds blinking and have modified the code to display Frequency (averaged over a ten cycle loop) on the LCD as follows:

' Define LCD registers and bits
Define	LCD_DREG	PORTC
Define	LCD_DBIT	0
Define	LCD_RSREG	PORTA
Define	LCD_RSBIT	5
Define	LCD_EREG	PORTC
Define	LCD_EBIT	4
Define	LCD_BITS	4
Define	LCD_LINES	2


CMCON0 = %00000111		' Disable comparators
ANSEL = %00000000		' Set PORTA as digital I/O
TRISC = 0               ' Set PORTC as output
TRISA.1 = 0             ' Make TOCKI input
OPTION_REG.0 = 0        ' Prescaler 1:1
OPTION_REG.1 = 0        ' 
OPTION_REG.2 = 0        '
OPTION_REG.3 = 1        ' Prescaler assigned to WDT
OPTION_REG.4 = 0        ' Increment on low-to-high transition
OPTION_REG.5 = 1        ' Clock on T0CKI-pin
OPTION_REG.6 = 0        '
OPTION_REG.7 = 1        '

OSCCON = %01110101      ' Set clock frequency to 8MHz
define OSC  8


' Included the interrupt system
INCLUDE "DT_INTS-14.bas"
INCLUDE "ReEnterPBP.bas"

' When compiling for the 16F684 DT-Ints tells us to add these variables so we do that
wsave VAR BYTE $20 SYSTEM
wsave1 VAR BYTE $A0 SYSTEM

TMR1_Reload CON 45536           ' Reload value for ~100Hz interrupt frequency at 8MHz, prescaler 1:1

TMR1_Temp VAR WORD              ' Temporary variable use for reloading the timer
IntCount VAR BYTE               ' Keep track of number of interrupts
oldCount VAR BYTE
newCount VAR BYTE
Frequency VAR WORD
UpdateDisplay VAR BIT

LED1 VAR PortA.0
LED2 VAR PortA.1

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  _ISR,   PBP,  yes
    endm
    INT_CREATE            ; Creates the interrupt processor
ENDASM

T1CON.0 = 1                       ' Start TMR1
@   INT_ENABLE  TMR1_INT  ; Enable Timer 1 Interrupts

Main:
'    Toggle LED1
'    Pause 1000
'    Goto Main

    if intCount = 0 then
        LCDOUT $FE, $02, "NewCount: ", #newCount, "  "
        LCDOUT $FE, $C0
        LCDOUT "Frequency: ", #Frequency, "   "
        Frequency = 0
    endif
Goto Main
 
' This is the interrupt routine for the TMR1 interrupt.
ISR:
    T1CON.0 = 0                         ' Stop timer
    TMR1_Temp.HighByte = TMR1H          ' Get current "time"
    TMR1_Temp.LOWBYTE = TMR1L
    TMR1_Temp = TMR1_Temp + TMR1_Reload ' Add reload value to get correct interval
    TMR1H = TMR1_Temp.HIGHBYTE          ' Move result back to timer 
    TMR1L = TMR1_Temp.LOWBYTE
    newCount =  TMR0 - oldCount
    oldCount = TMR0
    T1CON.0 = 1                         ' Start timer
    IntCount = INtCount + 1             ' Increment interrupt counter
    Frequency = Frequency + newCount
    If IntCount = 9 THEN
        Frequency = Frequency/10
        IntCount = 0
    ENDIF
@ INT_RETURN

OK, I appreciate that the Frequency readout isn't really the true frequency but I just wanted to prove the averaging routine.

Onwards and upwards... What's next?

Cheers
Barry
VK2XBP

[HenrikOlsson]

Ioannis,
Not sure I understand.... it will toggle LED1 once every second which means it will blink at 0.5Hz - isn't that what I wrote?

Barry,
Excellent! I wouldn't check IntCount in the main routine like that. Instead I'd check IntCount in the ISR and set a flag (UpdateDisplay or whatever). The main routine then checks this flag, executes the code and resets the flag. The reason for this is that when the code grows the Main routine may "miss" the when IntCount=0 (depending on what else it has to do and how long it takes). If you instead use the flag/semaphore method the Main routine WILL see that it's time to update display - when it gets around to it.

OK, now that you have a stable time base and the pulses counted in hardware it's time to add in the PID again. The ISR would look something like:

ISR:

    T1CON.0 = 0                         ' Stop timer
    TMR1_Temp.HighByte = TMR1H          ' Get current "time"
    TMR1_Temp.LOWBYTE = TMR1L
    TMR1_Temp = TMR1_Temp + TMR1_Reload ' Add reload value to get correct interval
    TMR1H = TMR1_Temp.HIGHBYTE          ' Move result back to timer 
    TMR1L = TMR1_Temp.LOWBYTE
    T1CON.0 = 1				' Start timer

    ' Get the current motor velocity
    newCount =  TMR0 - oldCount
    oldCount = TMR0

    ' Calculate error and run PID
    pid_Error = SetPoint - newCount
    GOSUB PID

    IntCount = IntCount + 1             ' Increment interrupt counter
    If IntCount = 9 THEN
        UpdateDisplay = 1
        IntCount = 0
    ENDIF

@ INT_RETURN

Your setpoint in this case is pulses per interrupt period, not actual frequency in Hz.

And the Main routine perhaps something like:

UpdateDisplay VAR BIT
Main:
   If UpdateDisplay THEN
     'LCDOUT.....
     'LCDOUT.....
   UpdateDisplay = 0
Goto Main

This is untested but I'm sure you'll get the idea.

/Henrik.

[Ioannis]

Ooops, yes Henrik. Sorry about that. Thought it was 0.5 second and not Hz as you stated.

Ioannis

[Aussie Barry]

OK, now I am a little confused....
You said that Setpoint now becomes pulses per interrupt period but how is this referenced to the ADCin result of my speed set trimpot?
Shouldn't the setpoint always be derived from the setting of the speed set trimpot and the error be calculated from the pulses per interrupt period?

Cheers
Barry
VK2XBP

[HenrikOlsson]

Yes, what I mean is that if you previously had your setpoint scaled directly in Hz it now needs to be scaled in pulses/interrupt period.

/H.

[Aussie Barry]

OK. Now I understand.
Setpoint was previously read via ACDin (0-1023).
ADValue was scaled in pulses per 100ms (approx 0-550)

In the new setup, variable NewCount (replacing ADValue) can range from 0-255 so I propose to convert the ADCin result from 10-bit to 8-bit
Setpoint = Setpoint>>2
so that the error term does not get too large and gain terms can be kept to a manageable size.

I will let you know how things pan out after tonight's round of experimants.

Cheers
Barry
VK2XBP

[Aussie Barry]

Things have been going too well for too long. A crach and burn situation was iminent!
Things started falling apart once I pieces everything together.

For starters, should I be able to use the serial LCD (debug statements) on RA5 with the DT-interrupts and counters on TMR0 and TMR1?
The LCD screen is completely garbled.

I have modified the circuit so that the three ADCin pots for Kp, Kd and Ki terms are on AN4, AN5 and AN6 and the encoder wheel pulse train is fed to M0CKI (pin 11). Circuit diagram is attached here incPID_16F684_V6.pdf

I am in the process of cleaning up the program (making the PID routine as an included file as per Henrik's suggestion). I will post the code soon.

In the mean time, any comments regarding the use of the serial LCD with DT-interrupts happening in the background would be greatly appreciated.

Cheers
Barry
VK2XBP