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Altera_Forum's avatar
Altera_Forum
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11 years ago

Interval Timer Core Interrupt for Nios II

I have seen many examples of using PIO cores to generate interrupts...say for button presses, and I have a grasp on those, but I am looking for a clear example of generating an interrupt using the timer core. My hardware is setup to generate a 1ms interval clock (see image attached for the setup) to IRQ 1 (high value interrupt) as I want to perform a specific task every millisecond (for example take a reading from an ADC), but I cannot grasp how to properly make this happen in the C code (I'm new to C programming not to hardware design...so it's the programming that I'm having issue with). If someone could help out a bit with a clear and small example of this that would be helpful, or point me in a direction where there is an example. Thanks, Jason

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Initialize the interrupt in your main application code this way: 

    
  // register the timer irq to be serviced by handle_timer_interrupt() function 
 alt_irq_register(SYS_CLK_TIMER_IRQ, 0, handle_timer_interrupt);
 // activate the time
 IOWR_ALTERA_AVALON_TIMER_CONTROL(SYS_CLK_TIMER_BASE, 
                 ALTERA_AVALON_TIMER_CONTROL_CONT_MSK  
               | ALTERA_AVALON_TIMER_CONTROL_START_MSK
               | ALTERA_AVALON_TIMER_CONTROL_ITO_MSK);

    This is the template for the interrupt service function: 

    
void handle_timer_interrupt(void*p, alt_u32 param)
{
   // clear irq status in order to prevent retriggering
   IOWR_ALTERA_AVALON_TIMER_STATUS(SYS_CLK_TIMER_BASE, 0);
   // your isr code here
   // ....
}
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    11 years ago

    Thanks for the reply, seems very straight forward.

    For the pushbutton interrupts, the code seemed to pass the edge capture register around using pointers, is this not necessary with the interval timer (Using the timer TO bit in the status register)? Or would that be for using the counter in another manner?