using darrel taylor's instant interrupts

[Michael Wakileh]

Hi everyone...
I just had a glace at Darrel Taylors great instant interrupts page (http://darreltaylor.com/DT_INTS-14/intro.html),
and I would like to apply these in the near future.

I would like to learn to have interrupts after a certain amount of time/manually preload the timer.. For example, to
make a light toggle every 70ms, I could use timer 1, prescaler 1:2 and preload of 30536 (thanks Mister E!).

I figured that I could base my code on:
the blinky light code http://darreltaylor.com/DT_INTS-14/blinky.html
the timer template http://darreltaylor.com/DT_INTS-14/TimerTemplate.html

I HAVE 2 QUESTIONS:

QUESTION 1: looking at the blinky light code: Do I understand correctly that the timer is still running while the interrupt handler is executing.


QUESTION 2 deals with altering the timer template code:
I figure it would be easiest for me to changing the code which calculates the timer reload constant. here it is:

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 - ((25000 / Freq) * (OSC*10/Prescaler))
if ((TimerReload < 0) || (TimerReload > (65535-ReloadInst)))
error Invalid Timer Values - check "OSC", "Freq" and "Prescaler"
endif
else
error Invalid Prescaler
endif
ENDASM


QUESTION 2: CAN THIS SIMPLY BE REPLACED BY

ASM
TimerReload = 30536
ENDASM


OR HAVE I MISSED SOMETHING?

[Charles Linquis]

#1 The timers run as long as they are enabled, so they will run in while you are in your ISR.

#2 You can reload (or pre-load) the timers at any time with any number - but you MUST load the high byte first.

[Darrel Taylor]

Since it takes 8 instructions to reload the timer, the actual number would be 30540 for 70ms.

But,... the TimerReload is an External Constant so you can't just give it a value like it's a variable.

You could change the ...

TimerReload CON EXT

-- to --

TimerReload CON 30540

But, if you want it to be easily changable, you might want to change the original code to this.

;--- Change these to match the desired interrupt frequency -------------------
;--- See http://DarrelTaylor.com/DT_INTS-14/TimerTemplate.html for more Info.
@Interval   = 70                  ; Interval of Interrupts in ms
@Prescaler  = 2                   ; Timers Prescaler setting
T1CON = $10                       ; $10 = Prescaler 1:2, TMR1 OFF
; $00=1:1, $10=1:2, $20=1:4, $30=1:8 --  Must match @Prescaler value



;---[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)*Interval)/1000)
    if ((TimerReload < 0) || (TimerReload > (65535-ReloadInst)))
        error Invalid Timer Values - check "OSC", "Interval" and "Prescaler"
    endif
  else
      error Invalid Prescaler
  endif
ENDASM

Then you can just change the Interval and Prescaler numbers to anything you wanted, without having to recalculate the Reload value.

hth,

[Michael Wakileh]

Thanks...you rock!!!

[Darrel Taylor]

Sometimes I wonder about that Rock part.

When I looked back at your first post, I saw.

QUESTION 2: CAN THIS SIMPLY BE REPLACED BY

ASM
TimerReload = 30536
ENDASM

Ummm, the answer to that should have been....
YES! Exactly that! (except 30540).

Would have worked great.
Can't imagine what I was thinking. Doh!

LOL,

[Michael Wakileh]

Hi Darell...Your above code will nevertheless be of value for many...

I'v finally just about finished writing my first timer template/instant interrupts based program. It just has 1 little bug when compiling...
If anyone has time, please take a look at this code snippet:

I am trying to use HPWM on a 16f690 in the main program loop.
The controlling variable "enabler" is determined by code in the timer1interrupt handler. When it is =1 the hpwm is turned on briefly.

Turning the HPWM on and off is where I have my problem..
I get WARNING Bad token " " for the 2 lines that set t2con in the main program loop, but not for the line setting t2con just before the main program loop. Any ideas?

best regards,
mike

------------------------------------------------------------------------
DEFINE OSC 4
OSCCON = %01100110 'should be OK too
ANSEL = $00
ANSELH = 0
ccp1con = 0
CM1CON0 = 0
CM2CON0 = 0

DEFINE I2C_HOLD 1
DPIN1 var PORTb.4 ' I2C data pin
CPIN1 var PORTb.6 ' I2C clock pin

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

enabler var bit

' LOTS MORE VARIABLES DECLARED HERE

ASM
INT_LIST macro ' use the format IntSource, Label, Type, ResetFlag?
INT_Handler TMR1_INT, ReloadTMR1, ASM, no
INT_Handler TMR1_INT, _MATHhandler, PBP, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

T1CON = $15 'prescaler; timer on
@ INT_ENABLE TMR1_INT ; enable Timer 1 interrupts

T2CON = $00 'HERE I DON'T GET A WARNING

main:
IF enabler = 1 THEN 'this variable controlls possible hpwm activation
TRISC = 1 'Datasheet said to turn off pwm outputs first
PR2 = 63 'Timer 2 period register
CCPR1L = 60 'MSBS of DUTYCYCLE
CCP1CON = %00001100 'CCP1M<3:0> = %1100 P1M<1:0> = %00 'turn on pwm…
PSTRCON = $0F '%00001111 PULSE STEERING CONTROL REGISTER- send same pwm signal to 4 outputs

T2CON = %00000100 ' HERE I GET A WARNING -precaler 1:1, postcaler 1:1, bit 2 = Timer2 ON

TRISC = 0
enabler = 0
PAUSE 100 'I could even change the vibration time by software (pause x)
CCP1CON = 0 'TURN OFF HPWM
T2CON = %00000000 'HERE I GET A WARNING -TURN OFF TMR2 - minimize power constumption

TMR2 = 0 'SHOULD RESET THE TIMER
endif
goto main


MATHhandler:

'ROUTINES THAT DETERMINE WHEN THE VARIABLE ENABLER=1 thus activating a short pwm signal in the main program

@ INT_RETURN



ASM
TimerReload = 30540
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
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
StartTimer:
Timer1 = TimerReload ; Load Timer
TMR1ON = 1 ; start timer
RETURN
StopTimer:
TMR1ON = 0 ; stop timer
RETURN
--------------------------------------------------------------------------