#include <stdint.h>
 
#define UART0_BASE_ADDR 0x101f1000 // UART address
#define UART0_DR (*((volatile uint32_t *)(UART0_BASE_ADDR + 0x000))) // UART Data Register
#define UART0_IMSC (*((volatile uint32_t *)(UART0_BASE_ADDR + 0x038))) // UART Interrupt Mask Set/Clear Register
 
#define VIC_BASE_ADDR 0x10140000 // Vectored Interrupt Controller Base Address
#define VIC_INTENABLE (*((volatile uint32_t *)(VIC_BASE_ADDR + 0x010))) //  Vectored Interrupt Controller Enable Interrupt address
 
// On interrupt print the received character to UART0_DR and move on
void __attribute__((interrupt)) irq_handler() {
 /* echo the received character + 1 */
 UART0_DR = UART0_DR + 1;
}
 
/* all other handlers are infinite loops */
void __attribute__((interrupt)) undef_handler(void) { for(;;); }
void __attribute__((interrupt)) swi_handler(void) { for(;;); }
void __attribute__((interrupt)) prefetch_abort_handler(void) { for(;;); }
void __attribute__((interrupt)) data_abort_handler(void) { for(;;); }
void __attribute__((interrupt)) fiq_handler(void) { for(;;); }
 
void copy_vectors(void) {
 extern uint32_t vectors_start;
 extern uint32_t vectors_end;
 uint32_t *vectors_src = &vectors_start;
 uint32_t *vectors_dst = (uint32_t *)0;
 
while(vectors_src < &vectors_end)
 *vectors_dst++ = *vectors_src++;
}
 
void main(void) {
 /* enable UART0 IRQ */
 VIC_INTENABLE = 1<<12; // Enable interrupts - 12th bit in register VIC_INTENABLE
 /* enable RXIM interrupt */ // RSIM - receive FIFO Imterrupt Mask
 UART0_IMSC = 1<<4; // 4th bit in register UART0_IMSC
 for(;;);
}