trap.c

#include "os.h"

extern void trap_vector(void);
extern void uart_isr(void);
extern void timer_handler(void);
extern void schedule(void);
extern void do_syscall(struct context *cxt);

void trap_init()
{
  /*
   * set the trap-vector base-address for machine-mode
   */
  w_mtvec((reg_t)trap_vector);
}

void external_interrupt_handler()
{
	int irq = plic_claim();

	if (irq == UART0_IRQ){
      		uart_isr();
	} else if (irq) {
		printf("unexpected interrupt irq = %d\n", irq);
	}
	
	if (irq) {
		plic_complete(irq);
	}
}

reg_t trap_handler(reg_t epc, reg_t cause, struct context *ctx)
{
  reg_t return_pc = epc;
  reg_t cause_code = cause & MCAUSE_MASK_ECODE;

  if (cause & MCAUSE_MASK_INTERRUPT)
  {
    /* Asynchronous trap - interrupt */
    switch (cause_code)
    {
    case 3:
      uart_puts("software interruption!\n");
      int id = r_mhartid();
      *(uint32_t*)CLINT_MSIP(id) = 0;
			schedule();
      break;
    case 7:
			uart_puts("timer interruption!\n");
			timer_handler();
      break;
    case 11:
      uart_puts("external interruption!\n");
			external_interrupt_handler();
      break;
    default:
      printf("Unknown async exception! Code = %ld\n", cause_code);
      break;
    }
  }
  else
  {
    /* Synchronous trap - exception */
    printf("Sync exceptions! Code = %ld\n", cause_code);
		switch (cause_code) {
		case 8:
			uart_puts("System call from U-mode!\n");
			do_syscall(ctx);
			return_pc += 4;
			break;
		default:
			panic("OOPS! What can I do!");
			//return_pc += 4;
		}
  }

  return return_pc;
}

void trap_test1()
{
  /*
   * Synchronous exception code = 7
   * Store/AMO access fault
   */
  *(int *)0x00000000 = 100;

  /*
   * Synchronous exception code = 5
   * Load access fault
   */
  // int a = *(int *)0x00000000;

  uart_puts("Yeah! I'm return back from trap!\n");
}