Interrupts

Cat systems support CPU interrupts which immediately stop what the CPU is doing and jump the instruction pointer to new code. You may trigger an interrupt with the int instruction manually, interrupts are also triggered by errors and user input.

Interrupts 0x00-0x0F are considered error interrupts and will halt the machine by default if not handled. All other interrupts will by default do nothing.

List

The following interrupts are given meaning by default:

Interrupt ID	Name	Args	Handleable	Description
0	Page Fault	stack 32 bit pointer - accessed memory	true	Memory could not be accessed (out of bounds, or forbidden)
1	Invalid Instruction		true	Instruction opcode or arguments were invalid
2	Divide by zero		true	Tried to divide by zero
3	RESERVED
4	RESERVED
5	RESERVED
6	RESERVED
7	RESERVED
8	RESERVED
9	RESERVED
a	RESERVED
b	RESERVED
c	RESERVED
d	RESERVED
e	RESERVED
f	RESERVED
70	Receive Input	r1 - device id, r2 - input type, r3 - value	true
80	Write to sout	r1 - pointer to string (null terminated)	false
81	Halt		false	Pause execution permanently
82	Shutdown		false	Poweroff
83	Reset		false	Restart (ip=0)
84	Get Display Buf Start		false	Returns the start address of the display buffer in r0
85	Get Uptime MSEC		false	Returns the uptime in milliseconds in r0
86	Refresh Screen		false	Update the display with new data in the display buffer
90	DEBUG: Print Number	r1 - number to print	false	Prints a number with a \n, only possible in debug mode

As shown above, some interrupts exist as function calls into the system, allowing you to do things like write to the VM's console. You can call them like functions.

Handling

You may handle interrupts by constructing an interrupt handler table and then set the IT register to a pointer to it. The structure of the table is as follows:

Offset	Field	Size (Bytes)
0x00	Entry Count	1
0x01	Entries	5 per entry

Then each entry is as follows:

Offset	Field	Size (Bytes)
0x00	Interrupt Code	1
0x01	Handler Pointer	4