Writing a PS/2 mouse driver for your hobby OS

It took me a while to search for a good tutorial on how to write a PS/2 mouse driver for a hobby OS. Luckily, I was able to make an existing driver work. So for those who are having trouble writing one, I came up with this guide. However, I do not take full credit in the codes that I will be posting.

I assume that your hobby OS is 32-bit targetted on x86 machines. The following outlines the steps.

1. Program the 8259 controller to enable IRQ2, the cascade line. The PS/2 mouse IRQ is IRQ12 which is in the slave PIC. Normally the IRQ numbers are remapped in 32-bit OSes.
   

   #define IRQ_TIMER 1
   #define IRQ_CASCADE 4
   #define IRQ_KEYBOARD 2
   #define IRQ_FDC 64
   #define IRQ_MOUSE 16
   void program8259(unsigned char b){
   unsigned char b1=0xFF;
   //remap the IRQs
   outportb(0x20,0x11);
   outportb(0xA0,0x11);
   outportb(0x21,0x20); //IRQ0-IRQ7 -> interrupts 0x20-0x27
   outportb(0xA1,0x28); //IRQ8-IRQ15 -> interrupts 0x28-0x2F
   outportb(0x21,4);
   outportb(0xA1,2);
   outportb(0x21,1);
   outportb(0xA1,1);
   b1^=b;
   outportb(0x21,b1);
   outportb(0xA1, inportb(0xA1) & ~0x10);  //enable IRQ12
   };
   
   //Here's the call to enable needed IRQ Lines called usually in the main() function
   program8259(IRQ_TIMER | IRQ_KEYBOARD | IRQ_FDC | IRQ_CASCADE);
   

   
   
2. And here's the driver code courtesy of SANiK.
   

   //Mouse.inc by SANiK
   //License: Use as you wish, except to cause damage
   unsigned char mouse_cycle=0;
   signed char mouse_byte[3];
   signed char mouse_x=0;
   signed char mouse_y=0;
   
   /* The interrupt handler */
   void mouse_irq(){
   DWORD flags;
   switch(mouse_cycle){
   case 0:
   mouse_byte[0]=inportb(0x60);
   mouse_cycle++;
   break;
   case 1:
   mouse_byte[1]=inportb(0x60);
   mouse_cycle++;
   break;
   case 2:
   mouse_byte[2]=inportb(0x60);
   mouse_x=mouse_byte[1];
   mouse_y=mouse_byte[2];
   mouse_cycle=0;
   break;
   }
   }
   
   inline void mouse_wait(unsigned char  a_type){
   unsigned int _time_out=100000; //unsigned int
   if(a_type==0){
   while(_time_out--){ //Data
   if((inportb(0x64) & 1)==1){
   return;
   }
   }
   return;
   }else{
   while(_time_out--){ //Signal
   if((inportb(0x64) & 2)==0){
   return;
   }
   }
   return;
   }
   }
   
   inline void mouse_write(unsigned char a_write){
   //Wait to be able to send a command
   mouse_wait(1);
   //Tell the mouse we are sending a command
   outportb(0x64, 0xD4);
   //Wait for the final part
   mouse_wait(1);
   //Finally write
   outportb(0x60, a_write);
   }
   
   unsigned char mouse_read(){
   //Get's response from mouse
   mouse_wait(0);
   return inportb(0x60);
   }
   
   void installmouse(){ /* This enables the mouse, called in main() */
   unsigned char _status;
   
   //Enable the auxiliary mouse device
   mouse_wait(1);
   outportb(0x64, 0xA8);
   
   //Enable the interrupts
   mouse_wait(1);
   outportb(0x64, 0x20);
   mouse_wait(0);
   _status=(inportb(0x60) | 2);
   mouse_wait(1);
   outportb(0x64, 0x60);
   mouse_wait(1);
   outportb(0x60, _status);
   
   //Tell the mouse to use default settings
   mouse_write(0xF6);
   mouse_read();  //Acknowledge
   
   //Enable the mouse
   mouse_write(0xF4);
   mouse_read();  //Acknowledge
   //Depends on your OS!
   setinterruptvector(0x2C,idtbase,0x8E,mousewrapper,SYS_CODE_SEL);
   printf("Mouse successfully initialized.\n");
   }
   
   void get_mouse_pos(signed char *x,signed char *y){
   *x=mouse_x;
   *y=mouse_y;
   }
   

   
   
3. The mousewrapper code is important for the IRET so it is written in assembly. It just actually calls mouse_irq defined in the driver above..
   

   global mousewrapper
   mousewrapper:
   push ebp
   push gs
   push fs
   push es
   push ss
   push ds
   pusha
   call mouse_irq
   ;re-enable interrupts, this is IMPORTANT!
   mov al,0x20
   out 0xA0,al
   out 0x20,al
   popa
   pop ds
   pop ss
   pop es
   pop fs
   pop gs
   pop ebp
   iret
   

That's it!Enjoy your mouse!