Nios II Classic Software Developer’s Handbook

ID 683282
Date 5/14/2015
Public
Document Table of Contents

8.2.7.1. An ISR to Service a Button PIO Interrupt

This example is based on a Nios II system with a 4-bit PIO peripheral connected to push buttons. An IRQ is generated any time a button is pushed. The ISR code reads the PIO peripheral’s edge capture register and stores the value to a global variable. The address of the global variable is passed to the ISR in the context pointer.

Example 8–1. An ISR to Service a Button PIO Interrupt

#include "system.h"
#include "altera_avalon_pio_regs.h"
#include "alt_types.h" 
#ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
static void handle_button_interrupts(void* context)
#else
static void handle_button_interrupts(void* context, alt_u32 id)
#endif
{
/* Cast context to edge_capture's type. It is important that this
be declared volatile to avoid unwanted compiler optimization. */
volatile int* edge_capture_ptr = (volatile int*) context;
/*
* Read the edge capture register on the button PIO.
* Store value.
*/
*edge_capture_ptr =
IORD_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE);
/* Write to the edge capture register to reset it. */
IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0);
/* Read the PIO to delay ISR exit. This is done to prevent a
spurious interrupt in systems with high processor -> pio
latency and fast interrupts. */
IORD_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE);
}