Changing the sines frequency?

[pxidr84]

Hi everyone,

I'm again here with my three-phase sines.

All works great, I can change the frequency (by varying the interrupt "timer" variable) and the amplitude of my sines (by varying the "amplitude" variable).

But something is strange with the timer : the output sines frequency is not proportinal with the timer value. There is what I get from real experimentations :


Of course, for the calculation of U/F variables, is far more complicated.

So, how I can calculate the output frequency of my sines internally by the PIC?
Or how I can change the sines frequency proportionally with an another method than varying "timer" variable?

Thanks.

Code :

' PIC initialization
DEFINE OSC 40      
DEFINE LCD_DREG PORTC
DEFINE LCD_EREG PORTD
DEFINE LCD_RSREG PORTD
DEFINE LCD_EBIT 0
DEFINE LCD_RSBIT 1
DEFINE LCD_COMMANDUS 4000
DEFINE LCD_DATAUS 100
DEFINE USE_LOWPRIORITY 1


' BAS includes
INCLUDE "DT_INTS-18.bas"
INCLUDE "ReEnterPBP-18.bas"
INCLUDE "ReEnterPBP-18LP.bas"
INCLUDE "Sine_table.bas"
INCLUDE "Freq_table.bas"


' Port registers configuration
TRISB=%11000000   ' PWM 0,1,2,3,4,5 outputs
TRISC=%00110000   ' +/- buttons


' PCPWM registers configuration
DTCON=%110        ' Deadtime (600ns)
PTCON0=%0         ' 1:1 postscale, Fosc/4 1:1 prescale, free running mode
PTCON1=%10000000  ' PWM time base is ON, counts up, 19.45kHz/4
PWMCON0=%1000000  ' PWM 0,1,2,3,4,5 set in pair mode
PWMCON1=%1        ' PWM timer sync configuration


' PWM calculation variables
ustep var byte
vstep var byte
wstep var byte
uduty var word
vduty var word
wduty var word
timer var word
amplitude var word
carrier VAR word
flag var bit


' Variables definition
ustep=72          ' 360 degrees phase angle
vstep=48          ' 240 degrees phase angle
wstep=24          ' 120 degrees phase angle
timer=64120       ' Timer adjust (64120=120Hz) 
amplitude=65535   ' Sinewave amplitude adjust (65535=max amplitude)
carrier=1023      ' Carrier frequency adjust (1023=13kHz)
flag=%0           ' Menu flag


' PWM carrier frequency register configuration
PTPERL=carrier.lowbyte  
PTPERH=carrier.highbyte

  
' Interrupt processors 
ASM
INT_LIST macro
         INT_Handler TMR1_INT,_pwmint,PBP,yes
         endm
         INT_CREATE 
    
INT_LIST_L macro
           INT_Handler TMR0_INT,_mainint,PBP,no
           endm
           INT_CREATE_L       
ENDASM

    
' Timers configuration
T1CON=%10000001
T0CON=%10000111


' Interrupts enable
@ INT_ENABLE TMR1_INT
@ INT_ENABLE TMR0_INT


' PWM calculation and update interrupt (Timer 1) 
pwmint:

' Timer 1 update
TMR1L=timer.lowbyte
TMR1H=timer.highbyte

' PWM U phase calculation
uduty=sine[ustep]
uduty=uduty<<4**amplitude+3

' PWM V phase calculation
vduty=sine[vstep]
vduty=vduty<<4**amplitude+3

' PWM W phase calculation
wduty=sine[wstep]
wduty=wduty<<4**amplitude+3

' PWM U, V and W update
PDC0L=uduty.lowbyte
PDC0H=uduty.highbyte
PDC1L=vduty.lowbyte
PDC1H=vduty.highbyte
PDC2L=wduty.lowbyte
PDC2H=wduty.highbyte

' Phase angle calculation
ustep=ustep-1
vstep=vstep-1
wstep=wstep-1

' Phase angle reinitialization
if ustep=0 then ustep=72
if vstep=0 then vstep=72
if wstep=0 then wstep=72

@ INT_RETURN


' Main program loop interrupt (Timer 0)
mainint:

' Debug display
if flag=0 then
LCDOUT $FE,$2,"Timer adjust :"
LCDOUT $FE,$C0,DEC5 timer
if PORTC.4=1 then timer=timer-1
if PORTC.5=1 then timer=timer+1
IF PORTC.4 AND PORTC.5=1 then flag=%1
else
LCDOUT $FE,$2,"Amp. adjust :"
LCDOUT $FE,$C0,DEC5 amplitude
if PORTC.4=1 then amplitude=amplitude-1
if PORTC.5=1 then amplitude=amplitude+1
endif

@ INT_RETURN

[HenrikOlsson]

Hi,
Running the PIC at 40Mhz and having a prescaler on TMR1 of 1:1 (no prescaler) makes it "tick" at 10MHz. Your sine-table, if I understand correctly contains 72 "steps" so you need 72 interrupts per second per Hz output frequency.

At 120 Hz output frequency you need 120*72= 8640Hz or an interrupt interval of 115.7us. At 10Mhz one "tick" is 0.1us so you need 1116 ticks between interrupts and therefor you should (theoretically) reload the timer with: 65536-1116 = 64420.

At 10Hz you need 720 interrupts per second or an interrupt interval of 1388.9us. That's 13889 ticks so you need to reload the timer with 65536-13889 = 51647.


Now, when the timer overflows and trips the interrupt a lot of things has to happend. The DT-Ints interrupt "engine" has to save all the PBP system varibles and this takes time. By the time the code actually gets to reloading TMR1 with your calculated reload value several hundred cycles have passed. If you then reload it with the "original", calculated value you are effectively "turning back the time" or reclaiming time that has already passed.

What you usually do is stop the timer, make a copy of its content and then ADD the reload value to the value of the copy. Then you put the value back in the timer and restart it. Obviously this too takes a couple of cycles so to be really accurate you need to tweak the reload values to account for it. Basically

TimerShadow VAR WORD
 
T1CON.0 = 0  'Stop TMR1
TimerShadow.HighByte = TMR1H
TimerShadow.LowByte = TMR1L
TimerShadow = TimerShadow + TimerReload
TMR1H = TimerShadow.HighByte
TMR1L = TimerShadow.LowByte
T1CON.0 = 1  'Restart TMR1

I see that you have 16bit read/write of TMR1 enabled, I don't know how that affects the above but I'd probably turn that off to begin with.

In the INT_List for the low priority interrupt you have the Reset_Flag set to NO for TMR0 - why is that? You don't seem to reset it "manually" in the ISR.

Finally, in your TMR0 interupt, don't do the LCDOUT etc in there. Set a flag and get out of there, then in your main routine you check the flag, if set do whatever and reset the flag.

[pxidr84]

Thanks Henrik (again), I will make some experiments with your tips.

[pxidr84]

Hi,
Running the PIC at 40Mhz and having a prescaler on TMR1 of 1:1 (no prescaler) makes it "tick" at 10MHz. Your sine-table, if I understand correctly contains 72 "steps" so you need 72 interrupts per second per Hz output frequency.

At 120 Hz output frequency you need 120*72= 8640Hz or an interrupt interval of 115.7us. At 10Mhz one "tick" is 0.1us so you need 1116 ticks between interrupts and therefor you should (theoretically) reload the timer with: 65536-1116 = 64420.

At 10Hz you need 720 interrupts per second or an interrupt interval of 1388.9us. That's 13889 ticks so you need to reload the timer with 65536-13889 = 51647.


Now, when the timer overflows and trips the interrupt a lot of things has to happend. The DT-Ints interrupt "engine" has to save all the PBP system varibles and this takes time. By the time the code actually gets to reloading TMR1 with your calculated reload value several hundred cycles have passed. If you then reload it with the "original", calculated value you are effectively "turning back the time" or reclaiming time that has already passed.

What you usually do is stop the timer, make a copy of its content and then ADD the reload value to the value of the copy. Then you put the value back in the timer and restart it. Obviously this too takes a couple of cycles so to be really accurate you need to tweak the reload values to account for it. Basically

TimerShadow VAR WORD
 
T1CON.0 = 0  'Stop TMR1
TimerShadow.HighByte = TMR1H
TimerShadow.LowByte = TMR1L
TimerShadow = TimerShadow + TimerReload
TMR1H = TimerShadow.HighByte
TMR1L = TimerShadow.LowByte
T1CON.0 = 1  'Restart TMR1

I see that you have 16bit read/write of TMR1 enabled, I don't know how that affects the above but I'd probably turn that off to begin with.

In the INT_List for the low priority interrupt you have the Reset_Flag set to NO for TMR0 - why is that? You don't seem to reset it "manually" in the ISR.

Finally, in your TMR0 interupt, don't do the LCDOUT etc in there. Set a flag and get out of there, then in your main routine you check the flag, if set do whatever and reset the flag.

Excuse me for my misunderstanding...
I've made some experiments with your routine, I can change the frequency, but even not proportionnaly, how do you integrate your routine into my program?

[HenrikOlsson]

Hi,
It's possible that you are simply trying to interrupt to fast and that it's overrunning it self - ie, another interrupt occurs before while servicing the first one. Try removing the all code from your ISR and replace with a simple TOGGLE PORTB.0 or whatever, measure the frequency of the output, that should give a clue as to what is going on.

[pxidr84]

Now I use this DT routine -> http://darreltaylor.com/DT_INTS-14/TimerTemplate.html

Hurray, I can set my desired interrupt frequency, so I can get my desired output frequency. It's the same principle of your code above.

But I've a little problem :

I like to define this ASM variable (@Freq = 10 ) to a PBP variable (for modify it in PBP and display it on the LCD for example).

I've tried this :
intfreq VAR WORD
intfreq=5000
@Freq = _intfreq

But it doesn't work at all.

Here's the DT timer template code :

; Initialize your hardware first

DEFINE OSC 20

INCLUDE "DT_INTS-14.bas"     ; Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ; Include if using PBP interrupts

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,   ReloadTMR1,   ASM,  no    ; MUST be first
        INT_Handler   TMR1_INT,   _T1handler,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

;--- Change these to match the desired interrupt frequency -------------------
;--- See http://DarrelTaylor.com/DT_INTS-14/TimerTemplate.html for more Info.
@Freq       = 10                  ; Frequency of Interrupts in Hz
@Prescaler  = 8                   ; Timers Prescaler setting
T1CON = $30                       ; $30 = Prescaler 1:8, TMR1 OFF
; $00=1:1, $10=1:2, $20=1:4, $30=1:8 --  Must match @Prescaler value

@ INT_ENABLE  TMR1_INT            ; enable Timer 1 interrupts
GOSUB StartTimer                  ; Start the Timer

;____Your Main Program goes here______________________________________________
Main:
  ;   ---- Your Main Program goes here ----
GOTO Main

;____This routine is Called on each TMR1 Interrupt____________________________
T1handler:
  ;   ---- Your interrupt routine goes here ----
  
@ INT_RETURN

;---[TMR1 reload - interrupt handler]-----------------------------------------
ASM                               ; Calculate Timer Reload Constant
ReloadInst  = 8                   ; # of Intructions used to reload timer
  if ((Prescaler == 1)||(Prescaler == 2)||(Prescaler == 4)||(Prescaler == 8))
MaxCount    = 65536 + (ReloadInst / Prescaler)
TimerReload = MaxCount - (OSC*1000000/4/Prescaler/Freq)
    if ((TimerReload < 0) || (TimerReload > (65535-ReloadInst)))
        error Invalid Timer Values - check "OSC", "Freq" and "Prescaler"
    endif
  else
      error Invalid Prescaler
  endif
ENDASM

@Timer1 = TMR1L                   ; map timer registers to a word variable
Timer1       VAR WORD EXT
TimerReload  CON EXT              ; Get the External Constant
TMR1ON       VAR T1CON.0          ; Alias the Timers ON/OFF bit

;---Reload Timer1------
ASM
ReloadTMR1
    MOVE?CT  0, T1CON, TMR1ON     ;  1     stop timer
    MOVLW    LOW(TimerReload)     ;  1     Add TimerReload to the 
    ADDWF    TMR1L,F              ;  1     value in Timer1
    BTFSC    STATUS,C             ;  1/2
    INCF     TMR1H,F              ;  1
    MOVLW    HIGH(TimerReload)    ;  1
    ADDWF    TMR1H,F              ;  1
    MOVE?CT  1, T1CON, TMR1ON     ;  1     start timer
  INT_RETURN
ENDASM

;---Start/Stop controls -----
StartTimer:
    Timer1  = TimerReload         ; Load Timer
    TMR1ON = 1                    ; start timer
RETURN

StopTimer:
    TMR1ON = 0                    ; stop timer
RETURN

[HenrikOlsson]

Hi
Aren't you using a PIC18F4431? If so you should use DT-INTS-18 but I suspect that is what you are doing even if you posted the DT-INTS-14 code?

Right, as far as I know the Freq variable isn't a variable it's an assembler constant. The TimerReload value is calculated at assembly time (not runtime) so once the code is assembled Freq no longer exists and can't be changed.

If you're using the timer template then it's the TimerReload value you should change in order to change the frequency - which is the same thing as we've been thru earlier in the thread.

/Henrik.