incPID Routine - Help Needed

[HenrikOlsson]

Great! Now lets put that on hold for a bit and see if we can get a timer interrupt going - then we'll glue it together.
I am a bit worried about the somewhat limited amount of RAM on '684 but we'll just have to see. I won't try to go into too much detail about DT-Ints, there's been several threads and several examples on the forum and obviosuly on Darrels site. If you don't already have the needed files you get them here. Place them either in the project directory or in the root folder of your PBP installation.

TMR1 is a 16bit timer and it causes an interrupt (if enabled) at rollover from $FFFF to 0. If we would let the timer free-run we'd get an interrupt every 65536th instruction cycle. At 8Mhz, that would be every 32.768ms or a frequency of ~30.5 Hz. If we want any other frequency we need to make sure that the timer doesn't start at 0 but at some other value. This is done by preloading the timer inside the interrupt service routine.

At 8Mhz one instruction cycle is 500ns. If we want an interrupt frequency of 100Hz we need the timer to roll over every 10ms, or once every 20000 instruction (20000*500ns=10ms). Because the timer interrupt when it rolls over we use 65536-20000=45536.


OK, now the code:

' 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 PortC.4
LED2 VAR PortC.5

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

 
' 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
    T1CON.0 = 1                         ' Start timer

    If IntCount = 19 THEN
        Toggle LED2
        IntCount = 0
    ENDIF
@ INT_RETURN

The main routine in the above code will blink LED1 at 0.5Hz. The timer interrupt should cause LED2 to blink at ~5Hz. The code compiles here but I haven't tested it. Obviosuly you need to add your CONFIG, TRIS, ANSEL, CMCON, whatever at the top too.

Give it a go, see if you can calculate and set the desired frequency.

/Henrik.

[Aussie Barry]

Thanks Henrik.

It looks good but I can't see how LED2 will ever toggle. I think there should be a line
IntCount = IntCount + 1
somewhere within the interrupt routine.

Anyway, I will have a play with it and let you know how I go.

Cheers
Barry
VK2XBP

[HenrikOlsson]

Definitely so. Somehow that fell out of there.....
Why do you need me for this ? ;-)

[Ioannis]

Nice job Henrik.

LED1 will toggle LED1 every 1 second not 0.5 (based on correct 8MHz clock).

Ioannis

[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