timer0 10ms setting check

[longpole001]

HI guys , i transfer some code from another processor which from the data sheet hs the same registers but seem to be getting a 20ms timer0 , not a 10ms interupt

all looks correct but it cant be , can someone have a look and see where i made the error

pic 18f46k80
osc32 internal,
timer 0 to give a 10ms interupt

;----- CONFIG1L Options --------------------------------------------------
    CONFIG XINST     = OFF 
    CONFIG SOSCSEL   = DIG        ; Digital (SCLKI) mode; I/O port functionality of RC0 and RC1 is enabled
    CONFIG INTOSCSEL = LOW        ; LF-INTOSC in low-power mode during Sleep
    CONFIG RETEN     = ON         ; Ultra Low power regulator is Enabled  (Controlled by SRETEN bit)when in sleep

;----- CONFIG1H Options --------------------------------------------------
    CONFIG IESO      = OFF 
    CONFIG FCMEN     = OFF
    CONFIG PLLCFG    = ON 
    CONFIG FOSC      = INTIO2     ; Internal RC oscillator  , PORTA.6 , PORTA.7 as I/O

   OSCCON   = %01100000     ' Select 32Mhz - using 8Mhz internal with PPLx4 in Config1H<3:0>  =  IDLEN =0 , 8Mhz , OSTS=0,RFIOFS=1,RC_Run (1x) OSC using PLL  
                            ' Bit 7 IDLEN =0 ( sleep mode when sleep instraction executed)
                            ' Bits 6-4 -  111 = 16Mhz , 110 = 8MHz ,101 = 4 MHz, 100 = 2MHz 011 = 1MHz
                            ' If INTTSRC=0 and MFIOSEL= 0 then 010 = HF-INTOSC/32 (500Khz), 001 = HF-INTOSC/64 (250Khz) ,000 = LF-INTOSC     (31.25Khz)
                            ' If INTTSRC=0 and MFIOSEL= 1 then 010 = MF-INTOSC    (500Khz), 001 = MF-INTOSC/2  (250Khz) ,000 = LF-INTOSC     (31.25Khz)
                            ' If INTTSRC=1 and MFIOSEL= 0 then 010 = HF-INTOSC/32 (500Khz), 001 = HF-INTOSC/64 (250Khz) ,000 = HF-INTOSC/512 (31.25Khz)
                            ' If INTTSRC=1 and MFIOSEL= 1 then 010 = MF-INTOSC    (500Khz), 001 = MF-INTOSC/2  (250Khz) ,000 = MF-INTOSC/16  (31.25Khz)
                            ' Note: INTSRC = OSCTUNE<7> and MFIOSEL = OSCCON2<0>
                            ' Bit 3 - OSTS = 0 - Osc startup time out  is ruinning from internal OSC ( HF, MF or LF-INTOSC) 
                            ' Bit 2 - HFIOFS =1 ( INTOSC Frq stable bit  -  1 = stable , 0 = not stable 
                            ' Bits 1-0 - 00= Dephalt Pri OSc ( OSC1/2 or HF-INTOSC with/without PLL set in FOSC,3:0> config1H <3.0>
                            '            01 = SOSC osc
                            '            1x = Internal osc ( LF, MF,HF-INTOSC)  
   
  ' OSCCON2 = $00            ' Bit 7 n/a , Bit 6 - SOSCRUN - Run status bit , Bit 5-4 n/a, 
                            ' Bit 3 = SOASCGO - Osc Start control bit 1 = OSC running , 0 = OSC shut off if no requests for it 
                            ' Bit 2 n/a , Bit 1 - MFIOFS 1= MFINTOSC stable  0 = Not stable 
                            ' Bit 0 MFIOSEL - 1 = MF-INTOSC replaces HF-ISTOSC Freq for 500Khz,250Khz,31.25KHz) 0 = MF-INTOSC not used 
  
   OSCTUNE = %01000000      ' Bit 7  - INTSRC - internal LF Source Select 1 = 31.25 from 16Mhz Internal /512 HF-INTOSC ) 0 = Internal 31khz OSC 
                            ' Bit 6 - PLLEN - 1 PLL enabled  , 0 = PLL disabled 
                            ' Bits 5-0 Frequancy callibaration 00000 = centre Frq

   ' ---------- Timer 0 Register Setups ---------------- 
    INTCON2.2 = 1          ' TMR0IP  - TIMER 0 Overflow Interupt Priority - 1 = High Priorty , 0 = Low Priority 
    T0CON.7 = 1             ' Bit7 - TMR0 1= Enable 0 = Stop timer
    T0CON.6 = 0             ' Bit6 - TMR0 8/16bit control 1= 8bit 0=16bit, 
    T0CON.5 = 0             ' Bit5 - TMR0 Clock Source 1=clk on T0CKI pin input 0=Internal clcck (Fosc/4)
    T0CON.4 = 0             ' Bit4 - TMR0 Source Edge Select 1= H/L of TOCKI 0= L/H of TOCKI , 
    T0CON.3 = 0             ' Bit3 - TMR0 PSA select 1=TMR0 Bypass Prescaler 0= CLK Input from Prescaler output      
    T0CON.2 = 0             ' Bit2-0 - Timer0 prescaler Rate Select bits 2-0(set to 1:256)         
    T0CON.1 = 0             ' 000 = 1:2  , 001= 1:4  , 010 = 1:8   , 011 = 1:16      
    T0CON.0 = 0             ' 100 = 1:32 , 101 = 1:64, 110 = 1:128 , 111 = 1:256

' ---------- Set up DT_INTS-18 Routine for Instant Interupt handling   -----------
   
     INCLUDE "DT_INTS-18.bas"       ; Base Interrupt System for 18FxxK80 processors
     INCLUDE "ReEnterPBP-18.bas"    ; Include if using PBP interrupts
    
ASM
INT_LIST macro	; IntSource  ,    Label    , Type, ResetFlag?

   INT_Handler TMR0_INT, _Timer0_Count,  PBP, yes      ; call Timer0_Count subroutine
  
 endm
 INT_CREATE								; Creates the Interrupt Processor
ENDASM

' ============ Timer 0 Interupt handler ================
 ' a 10 ms timer interupt 

  Timer0_Count:
    
    INTCON.5 = 0                 ' STOP TIMER
   T0Count1 = T0Count1 + 1      ' inc counter on interupt flag
    TMR0H = $63               ' preset Timer 0 to a 10ms timer
    TMR0L = $C0                              
    INTCON.5 = 1                 ' START TIMER
@ INT_RETURN
    RETURN

[towlerg]

As your error is double, it's likely a problem with the 2:1 prescaler. Perhaps your setting of T0CON is being overwritten in one of the include files.

Or your clock is running at 16Mhz.

George

[HenrikOlsson]

Not sure it's got anything to do with your problem but flipping INTCON.5 does not start/stop TMR0 - it enables/disables the interrupt.

  Timer0_Count:
    
    INTCON.5 = 0                 ' STOP TIMER   <----- No it doesn't
   T0Count1 = T0Count1 + 1      ' inc counter on interupt flag
    TMR0H = $63               ' preset Timer 0 to a 10ms timer
    TMR0L = $C0                              
    INTCON.5 = 1                 ' START TIMER       <------ No it doesn't
@ INT_RETURN
    RETURN

Also, verify that your oscillator is actually running at the expected frequency. A simple LED blinking at 10Hz will tell you if it's off bu a factor of 2.

/Henrik.

[longpole001]

YES CHECKED THE PRESCALLER AS SHOWN

osc as shown
ameding the interupt routine as follows changes nothing

it not clear what i missed

' ============ Timer 0 Interupt handler ================
 ' a 10 ms timer interupt 

  Timer0_Count:
    
      T0CON.7 = 0             ' Bit7 - TMR0 1= Enable 0 = Stop timer
    INTCON.5 = 0                 ' clear timer0 interupt IE 
   T0Count1 = T0Count1 + 1      ' inc counter on interupt flag
    TMR0H = $63               ' preset Timer 0 to a 10ms timer
    TMR0L = $C0                              
   INTCON.5 = 1                 ' enable Interupt 
    T0CON.7 = 1                  ' Bit7 - TMR0 1= Enable 0 = Stop timer
@ INT_RETURN
    RETURN

[longpole001]

yes i fixed it after puting in a pin to toggle found it was jumping out of the service routine

sorry guys

[longpole001]

also dont take the MIkro timer calculator at its word

i been testing lower osc +PPL for power usage ( lower the main osc the lower the current use)

when using thier calculator for 1mhz main osc + PPl - so entering the value of 4Mhz on the caclulator FOR 10MS , gives T0CON = $88 , TRM0H = $D8 TRM0L = $F0

which is does not give you a 10ms time it give you a 40ms time , as the t0con setting bit 3 uses the base osc bypass prescale ,

entering in the a main osc of 1mhz AND 10MS interupt give a T0CON= $88, TRM0H=F6,TRM0L=3C - which is correct

handy tool just need to know its not correct when timer0 on 18f gives a tocon = $88 - bypassing the prescaler

[HenrikOlsson]

For accurate timings you also need to take the interrupt latency and the time it takes to actually reload the timer registers into account.
The interrupt fires, then it takes a couple of hundred instructions to do the context saving etc before you actually get to reloading the timer for another 10ms period. If it's used for something like a clock it'll run slow.

What you usually do in the ISR is stop the timer, read it's value, then ADD the reload value (minus a fudge factor to account for the time the timer isn't running) to the value being read from the timer. Then you write the new value back and restart the timer. That way the interrupt latency is always compensated for.

/Henrik.

[towlerg]

....takes a couple of hundred instructions....

To save context?

George

[HenrikOlsson]

Yes, when you're using DT-Ints with an PBP-type ISR it has to save all the system variables when entering the ISR (and restore them on exit). The exact amount of time that takes can probably be different depending on device, if you're using LONGs, what PBP commands are being used in the program and so on. I've measured it a couple of times and the notes I can find at the moment says that the latency is around 20us on an 18F4431 running at 40MHz with a program compiled using LONGs.

20us at 40MHz is 160 instructions.

/Henrik.

[longpole001]

thanks for that , yes i dont need it too accurate for this requirement