RAM
Constants
startup init
exec
task switch

Tasks can be started up in random slots at any time


	flags	sp
W	0	0
X	0	0
Y	0	0
Z	0	0

startup:
	set all sp's to 0xff
	set multitasking flag

exec:
	set the sp of one of the slots to the value of the task to be run


irq:
    set aside regs (B)
    decrement timer
    if timer is < 1 
    {
	switch task:
	push all remaining registers (A)
      trynext:
	increment task number
	and task number with 0x03
	check stored sp for that task
	if (stored sp == 0xff)
	{
	    goto trynext:
	} if (stored sp <= 0xfe)
	{
	    start task (sp) in that slot:
		sp = slot's starting stack pointer
		push entry point onto stack
		push 0s onto the stack as (B) above
		push 0s onto the stack as (A) above
	} else {
	    move that sp into the SP
	    reset timer to max
	}
	pop all remaining registers
    }
    restore regs