TIMER1 too slow

[Flavio58]

I have activated a timer1 connected at a 32Khz oscillator to manage the date/time in my project.
The function to manage the overflow is this


#int_timer1
void clock_isr()
{
if(--int_count==0) {
++seconds;
int_count=INTS_PER_SECOND;
}
}

and this is the init procedure in the main funtion...

T1CON = 0x8F;
PIE1 = 1;
set_timer1(0x00);

enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);

The T1CON value 0x8F set the prescaler to 1:1 and set the bits to activate the timer1.
The interrupt routine work ....but the problem is that TIMER1 call the overflow interrupt only 1 time every 2 seconds....
I tried to change the overflow value to 8 bits but the result is the same ....
There are some strange init procedure to activate this timer ?

[ttelmah]

[Neutone]

Funny you should mention this. I posted some code just before the forum was moved. The code you posted is not going to work accuratly using the system clock because you round the number of ints per second. Try something like this. The variable Ticker is the number of instruction cycles remaining until the second count is incremented. During each interupt, decrement ticker by the number of instruction cycles per timer interupt. If Ticker is less than the number of instructions per interupt, increment seconds and add instruction cycles per second to ticker. This will be as reliable as using an extra crystle for keeping time. Long term accuracy is as good as the crystle. If a crystle has +-10PPM you could be off by 10 seconds in about 11.5 days. This also allows the code in main to check for flags that are set at regular intervals.

int1 Initialized=1;
int1 Clock_mS_Tic;
int1 Clock_S_Tic;
int32 Ticker;
#locate Ticker = 0x020
int8 Ticker_byte_2;
#locate Ticker_byte_2 = 0x022
Int32 Seconds;

#inline
void Initialize_RTC(void);
/********************************************************************
* Initialize RTC *
********************************************************************/
#inline
void Initialize_RTC(void)
{ Ticker = 19660800;
setup_timer_2 ( T2_DIV_BY_4, 0xff, 1 );
enable_interrupts( INT_TIMER2 );
}

/********************************************************************
* Service RTC *
********************************************************************/
#int_TIMER2
void TIMER2_isr()
{ Clock_mS_Tic=1;
if(--Ticker_byte_2)
{ Ticker+=19660800;
Seconds++;
Clock_S_Tic=1;
}
}

[regan]

To use Timer1 with a 32KHz crystal to get 1 second interrupts use the following code:

#define clk_reload 0x8000

// to setup the timer use:

void clk_init()
{
setup_timer_1(T1_CLK_OUT|T1_EXTERNAL|T1_DIV_BY_1);
set_timer1(clk_reload);
enable_interrupts(INT_TIMER1); // assuming INT_GLOBAL already enabled
}

// and the interrupt handler can be:

#int_timer1
void clk_isr()
{
set_timer1(clk_reload);
// put your code here.
}

regan.

[Mark]

It is better to add your reload time to the timer1 value to account for any latencies.