Adding support for Interrupts.

Squash-merging changes by @tanay-man.

Thanks!

src/cpu.c

@@ -2821,6 +2821,20 @@ void cpu_exec(cpu *c, u8 opcode) {
          (c->ip)+=2;
          break;
 
+      case 0xcd:
+         u8 operand = cpu_fetch(c);
+         printf("Interrupt called with argument %d",operand);
+         interrupt(c,operand);
+         break;
+
+      case 0xcc:
+         interrupt(c,3);
+         break;
+
+      case 0xcf:
+         iret(c);
+         break;
+
       default: break; /* nops and unused */
    }
    /* setting the segment override to 0 after executing every instruction */

src/cpu.h

@@ -40,7 +40,7 @@
 #include "jumps.h"
 #include "mul_div.h"
 #include "push_pop.h"
-
+#include "interrupts.h"
 /* cpu procs */
 cpu* cpu_make();
 void cpu_init(cpu* c);

src/interrupts.c

@@ -0,0 +1,20 @@
+#include "interrupts.h"
+
+void interrupt(cpu* c, u8 interrupt_type){
+  push16(c,c->flags);
+  resetTF(c);
+  resetIF(c);
+  push_r(c,c->cs);
+  push_r(c,c->ip);
+  u32 interrupt_pointer = interrupt_type*4;
+  c->ip = cpu_read_u16_at(c,interrupt_pointer);
+  c->cs = cpu_read_u16_at(c,interrupt_pointer+2);
+  return;
+}
+
+void iret(cpu* c){
+  c->ip = pop16(c);
+  c->cs = pop16(c);
+  c->flags = pop16(c);
+  return;
+}

src/interrupts.h

@@ -0,0 +1,23 @@
+
+#ifndef INT_H
+#define INT_H
+#include "push_pop.h"
+#include "flagops.h"
+#include "cpu.h"
+// case 0x90 NOP No operation   
+
+// case 0xcd INT interrupt
+// case 0xce INTO interrupt on overflow
+// case 0xcf IRET interrupt return
+
+// case 0xf4 HLT halt
+// case 0xfa CLI clear if ---> Already implemented
+// case 0xfb STI set if ---> Already implemented
+
+void interrupt(cpu* c,u8 interrupt_type);
+void into(void);
+void iret(cpu* c);
+void halt(void);
+
+
+#endif