Timer interrupt maxes out early

Hi,

Which controller are you using; also please paste the timer sub-routine ? 

Regards,

Gautam

Hi guatam, thank you very much for your quick reply. I am using the TMS320F28027.

Here is my code: http://pastebin.com/PnR1dB1P

I wrote an init_timer() function to initialize and start the timer and enable interrupts. please let me know if you need anything else

You mean to say that you need to generate timer for 1usec such that you can achieve timer interrupt at 1MHz ??

Yes this is exactly what I want to do. I need to send an SPI signal every 1us to acheive 1MSPS on my DAC

Cool, you can edit the PeripheralHeaderIncludes.h file and can achieve your target. I also have generated timer for as low as 1us but what issue I faced was, I was not able to achieve the same for 60MHz sysclock. I'd to reduce the sysclock to as low as to around 10-20MHz (off course without any prescaler). You can use the prescaler though.

I'm attaching the header file so that you can edit the value:

7870.PeripheralHeaderIncludes.h

Regards,

Gautam

The only change I see you have made in the header file is to add a macro definition for convenience, is that correct?

So what you are saying is to reduce the speed of the system clock and use a smaller timer period?

Yes... exactly! Check with 60Mhz itself; the least timer value you can achieve. Accordingly reduce the sysclock.

Regards,

Gautam

I don't think I quite understand. How will reducing the sysclk allow the timer to have a smaller period? Why is it that at 60MHz I can't have a timer period of 1us?

That was the issue I experienced! You can check it out by yourself. If you are able to achieve it using 60Mhz then its well and good.

Ah! I'll play around with it a bit more, but I've been messing with it for quite a while without much progress. And the documentation is very brief for the timer!

Thanks for your help! I'll let you know if I solve it. I have tried reducing the sysclk but I still cannot speed up the timer any more. Any value in the period register less than 500 seems to be equivalent to 500

Also check with this, after including Peripheral header file try implementing this code:

CpuTimer0Regs.PRD.all =  uSec1;        //uSec1 is from peripheral header file

for(;;) //infinite loop
{
  if(CpuTimer0Regs.TCR.bit.TIF == 1)
 {
  CpuTimer0Regs.TCR.bit.TIF = 1; // clear flag

    //-----------------------------------------------------------
    GpioDataRegs.GPBTOGGLE.bit.GPIO34 = 1; //Toggle GPIO34 (LD2)
   //-----------------------------------------------------------
 }

}

Monitor GPIO34 on DSO!

Regards,

Gautam

This is what I have been doing to see how fast I the timer interrupt period is. I wonder if it is something to do with timer0 interrupt being multiplexed by PIE. I will look into it a bit more

I switched the interrupt to timer2 so that the interrupt request goes straight to the cpu. This improved the speed a bit but not by the factor of 10 that I need.

Any example code relevant would be much appreciated.

Thanks again

Sorry mate, I won't be able to share any code with you. But the above routine is enough; just that you'll have to keep reducing the timer values in peripheral header file. Nothing more is required.

Regards,

Gautam