Working ISR example

[Altera_Forum]

Hello all, 

 I was developing some new hardware and had problems debugging my own ISR. I got the code below from Slacker( modified slightly), and it helped me quickly zoom into my new hardware problem, spurious interrupt. I run the code and hardware through Modelsim 6.0c and it works fine. For a new piece of HW, just change base address and make your own interrupt source, mine is a fifo read that causes an underflow ( and an interrupt).  I did see a problem with my component when I accidentally built my module with dynamic alignment instead of native. Of course I got incorrect reads( my peripheral is only 8 bits), but worse, my interrupt would be set and my isr would not work. Not sure why, but native alignment is correct for me anyway.  Hope this is useful for someone.  -Baycool  ******************************************  /* Includes */ # include "io.h"# include "system.h"# include "sys/alt_irq.h"# include <stdio.h># include <stdlib.h># include "alt_types.h"   const unsigned int CMD_AVALON_BASE = (unsigned int) 0x00100800; unsigned int check_fifo;  /* Assumes existence of SOPC component*/  /* The ISR for the irqgen component. */ static void handle_irqgen_isr(void* context, alt_u32 id) {  /* Extract the "count". */  int* count_ptr = (int*) context;  /* Set the count variable. */  *count_ptr = 1;  /* Clear the IRQ. */  IOWR(CMD_AVALON_BASE, 20, 1); }  /* "Initializes" the irqgen component.  * - Registers and ISR  */  static void init_irqgen(int* count) {  /* Register the ISR. */  alt_irq_register( 1, count, handle_irqgen_isr );   }  /* The main loop. Capture Interrupt */  int main(void) {  printf("Begin Cmd Avalon Test!\n");   /* A count variable which tracks if an interrupt has occured. */  int count = 0;  /* Initialize the irqgen component. */  init_irqgen( &count );    /* Cause Interrupt */  check_fifo = IORD(CMD_AVALON_BASE,0x0);  printf("Fifo is : 0x%X \n", check_fifo);    /* main loop */  while( 1 )  {    if( count == 1 )  {  printf(" Got interrupt, You lucky dog !! \n");  count = 0;  }  }   }