Altera DE1-SoC - Page 30

DE1-SOC COMPUTER SYSTEM WITH NIOS II For Quartus II 15.0
#include "key_codes.h" // defines values for KEY0, KEY1, . . .
extern volatile int key_pressed;
/********************************************************************************
* Pushbutton - Interrupt Service Routine
*
* This routine checks which KEY has been pressed. It writes this value to the global
* variable KEY_PRESSED.
********************************************************************************/
void pushbutton_ISR( void )
{
volatile int * KEY_ptr = (int *) 0xFF200050;
int press;
press = *(KEY_ptr + 3); // read the pushbutton interrupt register
*(KEY_ptr + 3) = press; // clear the interrupt
if (press & 0x1) // KEY0
key_pressed = KEY0;
else if (press & 0x2) // KEY1
key_pressed = KEY1;
else if (press & 0x4) // KEY2
key_pressed = KEY2;
else // press & 0x8, which is KEY3
key_pressed = KEY3;
return;
}
Figure 24. Interrupt service routine for the pushbutton keys.
30 Altera Corporation - University Program
2015